diff --git a/lib/microwaveprop/accounts/user.ex b/lib/microwaveprop/accounts/user.ex
index 99973c8a..6c68d3f1 100644
--- a/lib/microwaveprop/accounts/user.ex
+++ b/lib/microwaveprop/accounts/user.ex
@@ -21,6 +21,8 @@ defmodule Microwaveprop.Accounts.User do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @doc """
   Returns the email address that is automatically granted admin
   privileges on registration.
diff --git a/lib/microwaveprop/beacon_monitors.ex b/lib/microwaveprop/beacon_monitors.ex
index 1c413368..77e2b29b 100644
--- a/lib/microwaveprop/beacon_monitors.ex
+++ b/lib/microwaveprop/beacon_monitors.ex
@@ -16,6 +16,7 @@ defmodule Microwaveprop.BeaconMonitors do
   @doc """
   Returns all monitors for the given user, newest first.
   """
+  @spec list_monitors_for_user(User.t()) :: [BeaconMonitor.t()]
   def list_monitors_for_user(%User{id: user_id}) do
     Repo.all(
       from m in BeaconMonitor,
@@ -27,6 +28,7 @@ defmodule Microwaveprop.BeaconMonitors do
   @doc """
   Creates a new monitor for the given user with a freshly generated token.
   """
+  @spec create_monitor(User.t(), map()) :: {:ok, BeaconMonitor.t()} | {:error, Ecto.Changeset.t()}
   def create_monitor(%User{} = user, attrs) do
     %BeaconMonitor{user_id: user.id, token: generate_token()}
     |> BeaconMonitor.changeset(attrs)
@@ -39,6 +41,8 @@ defmodule Microwaveprop.BeaconMonitors do
   Returns `{:error, :not_found}` if the monitor does not exist or
   belongs to another user.
   """
+  @spec delete_monitor(User.t(), Ecto.UUID.t()) ::
+          {:ok, BeaconMonitor.t()} | {:error, :not_found} | {:error, Ecto.Changeset.t()}
   def delete_monitor(%User{id: user_id}, monitor_id) do
     query =
       from m in BeaconMonitor,
@@ -55,6 +59,7 @@ defmodule Microwaveprop.BeaconMonitors do
   @doc """
   Looks up a monitor by its token. Returns nil if not found.
   """
+  @spec get_monitor_by_token(String.t()) :: BeaconMonitor.t() | nil
   def get_monitor_by_token(token) when is_binary(token) do
     Repo.get_by(BeaconMonitor, token: token)
   end
@@ -62,6 +67,7 @@ defmodule Microwaveprop.BeaconMonitors do
   @doc """
   Returns a blank changeset for rendering the new-monitor form.
   """
+  @spec change_monitor(map()) :: Ecto.Changeset.t()
   def change_monitor(attrs \\ %{}) do
     BeaconMonitor.changeset(%BeaconMonitor{}, attrs)
   end
diff --git a/lib/microwaveprop/beacon_monitors/beacon_monitor.ex b/lib/microwaveprop/beacon_monitors/beacon_monitor.ex
index 3ff887bb..b6b3dc4b 100644
--- a/lib/microwaveprop/beacon_monitors/beacon_monitor.ex
+++ b/lib/microwaveprop/beacon_monitors/beacon_monitor.ex
@@ -23,10 +23,13 @@ defmodule Microwaveprop.BeaconMonitors.BeaconMonitor do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @doc """
   Changeset for user-controlled fields (name only for now).
   Token and user_id are assigned by the context, not cast from user input.
   """
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(monitor, attrs) do
     monitor
     |> cast(attrs, [:name])
diff --git a/lib/microwaveprop/beacons.ex b/lib/microwaveprop/beacons.ex
index b73fa213..56571333 100644
--- a/lib/microwaveprop/beacons.ex
+++ b/lib/microwaveprop/beacons.ex
@@ -20,6 +20,7 @@ defmodule Microwaveprop.Beacons do
     * `{:updated, %Beacon{}}`
     * `{:deleted, %Beacon{}}`
   """
+  @spec subscribe_beacons() :: :ok | {:error, term()}
   def subscribe_beacons do
     Phoenix.PubSub.subscribe(Microwaveprop.PubSub, @topic)
   end
@@ -29,6 +30,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Returns approved beacons ordered by most recently added."
+  @spec list_beacons() :: [Beacon.t()]
   def list_beacons do
     Repo.all(
       from b in Beacon,
@@ -38,6 +40,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Returns unapproved beacons awaiting admin review."
+  @spec list_pending_beacons() :: [Beacon.t()]
   def list_pending_beacons do
     Repo.all(
       from b in Beacon,
@@ -47,12 +50,14 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Gets a single beacon. Raises if not found."
+  @spec get_beacon!(Ecto.UUID.t()) :: Beacon.t()
   def get_beacon!(id), do: Beacon |> Repo.get!(id) |> Repo.preload(:user)
 
   @doc """
   Creates a beacon. When a user is provided they are recorded as the
   creator; anonymous submissions pass `nil` and leave `user_id` unset.
   """
+  @spec create_beacon(User.t() | nil, map()) :: {:ok, Beacon.t()} | {:error, Ecto.Changeset.t()}
   def create_beacon(user, attrs)
 
   def create_beacon(%User{} = user, attrs) do
@@ -70,6 +75,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Updates a beacon."
+  @spec update_beacon(Beacon.t(), map()) :: {:ok, Beacon.t()} | {:error, Ecto.Changeset.t()}
   def update_beacon(%Beacon{} = beacon, attrs) do
     beacon
     |> Beacon.changeset(attrs)
@@ -78,6 +84,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Marks a beacon as approved, making it visible in the public list."
+  @spec approve_beacon(Beacon.t()) :: {:ok, Beacon.t()} | {:error, Ecto.Changeset.t()}
   def approve_beacon(%Beacon{} = beacon) do
     beacon
     |> Ecto.Changeset.change(approved: true)
@@ -86,6 +93,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Deletes a beacon."
+  @spec delete_beacon(Beacon.t()) :: {:ok, Beacon.t()} | {:error, Ecto.Changeset.t()}
   def delete_beacon(%Beacon{} = beacon) do
     case Repo.delete(beacon) do
       {:ok, beacon} ->
@@ -98,6 +106,7 @@ defmodule Microwaveprop.Beacons do
   end
 
   @doc "Returns an `%Ecto.Changeset{}` for tracking beacon changes."
+  @spec change_beacon(Beacon.t(), map()) :: Ecto.Changeset.t()
   def change_beacon(%Beacon{} = beacon, attrs \\ %{}) do
     Beacon.changeset(beacon, attrs)
   end
diff --git a/lib/microwaveprop/beacons/beacon.ex b/lib/microwaveprop/beacons/beacon.ex
index cac204a5..df00a7e1 100644
--- a/lib/microwaveprop/beacons/beacon.ex
+++ b/lib/microwaveprop/beacons/beacon.ex
@@ -41,8 +41,10 @@ defmodule Microwaveprop.Beacons.Beacon do
   @keyings Enum.map(@keying_entries, fn {k, _} -> k end)
   @keying_labels Map.new(@keying_entries)
 
+  @spec keyings() :: [String.t()]
   def keyings, do: @keyings
 
+  @spec keying_label(String.t()) :: String.t()
   def keying_label(key), do: Map.get(@keying_labels, key, key)
 
   @doc """
@@ -50,6 +52,7 @@ defmodule Microwaveprop.Beacons.Beacon do
   notation. Integers are printed without a decimal; floats keep up to three
   decimals with trailing zeros trimmed.
   """
+  @spec format_mw(number() | nil | term()) :: String.t()
   def format_mw(nil), do: ""
 
   def format_mw(mw) when is_number(mw) do
@@ -70,6 +73,7 @@ defmodule Microwaveprop.Beacons.Beacon do
   def format_mw(mw), do: to_string(mw)
 
   @doc "Formats a frequency in MHz with comma separators (e.g. 10368 → \"10,368\")."
+  @spec format_freq(number() | nil | term()) :: String.t()
   def format_freq(nil), do: ""
 
   def format_freq(mhz) when is_number(mhz) do
@@ -110,6 +114,7 @@ defmodule Microwaveprop.Beacons.Beacon do
   Keying options for `Phoenix.HTML.Form.options_for_select/2`, grouped for a
   cleaner UI when dozens of weak-signal modes are present.
   """
+  @spec keying_options() :: [{String.t(), [{String.t(), String.t()}]}]
   def keying_options do
     [
       {"Simple",
@@ -158,8 +163,11 @@ defmodule Microwaveprop.Beacons.Beacon do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields [:frequency_mhz, :callsign, :lat, :lon, :power_mw, :height_ft, :keying]
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(beacon, attrs) do
     beacon
     |> cast(attrs, [
diff --git a/lib/microwaveprop/commercial.ex b/lib/microwaveprop/commercial.ex
index e788d252..525d8b02 100644
--- a/lib/microwaveprop/commercial.ex
+++ b/lib/microwaveprop/commercial.ex
@@ -7,24 +7,28 @@ defmodule Microwaveprop.Commercial do
   alias Microwaveprop.Commercial.Sample
   alias Microwaveprop.Repo
 
+  @spec enabled_links() :: [Link.t()]
   def enabled_links do
     Link
     |> where([l], l.enabled == true)
     |> Repo.all()
   end
 
+  @spec create_link(map()) :: {:ok, Link.t()} | {:error, Ecto.Changeset.t()}
   def create_link(attrs) do
     %Link{}
     |> Link.changeset(attrs)
     |> Repo.insert()
   end
 
+  @spec create_sample(map()) :: {:ok, Sample.t()} | {:error, Ecto.Changeset.t()}
   def create_sample(attrs) do
     %Sample{}
     |> Sample.changeset(attrs)
     |> Repo.insert()
   end
 
+  @spec weather_stations() :: [String.t()]
   def weather_stations do
     Link
     |> where([l], l.enabled == true and not is_nil(l.weather_station))
diff --git a/lib/microwaveprop/commercial/link.ex b/lib/microwaveprop/commercial/link.ex
index 47365aef..819f2996 100644
--- a/lib/microwaveprop/commercial/link.ex
+++ b/lib/microwaveprop/commercial/link.ex
@@ -20,9 +20,12 @@ defmodule Microwaveprop.Commercial.Link do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(label host community radio_type)a
   @optional_fields ~w(endpoint_a endpoint_b weather_station enabled)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(link, attrs) do
     link
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/commercial/sample.ex b/lib/microwaveprop/commercial/sample.ex
index ac9d632a..a2b72b29 100644
--- a/lib/microwaveprop/commercial/sample.ex
+++ b/lib/microwaveprop/commercial/sample.ex
@@ -39,12 +39,15 @@ defmodule Microwaveprop.Commercial.Sample do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(link_id sampled_at)a
   @optional_fields ~w(rx_power_0 rx_power_1 tx_power tx_freq_mhz rx_freq_mhz
     radio_temp_0_c radio_temp_1_c cur_tx_mod_rate remote_tx_mod_rate
     rx_capacity tx_capacity remote_tx_power remote_rx_power_0 remote_rx_power_1
     link_state link_uptime link_distance_m)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(sample, attrs) do
     sample
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/geo.ex b/lib/microwaveprop/geo.ex
index b0c430a7..09232851 100644
--- a/lib/microwaveprop/geo.ex
+++ b/lib/microwaveprop/geo.ex
@@ -4,6 +4,7 @@ defmodule Microwaveprop.Geo do
   @earth_radius_km 6371.0
 
   @doc "Great-circle distance between two points in km."
+  @spec haversine_km(number(), number(), number(), number()) :: float()
   def haversine_km(lat1, lon1, lat2, lon2) do
     dlat = deg_to_rad(lat2 - lat1)
     dlon = deg_to_rad(lon2 - lon1)
@@ -16,6 +17,7 @@ defmodule Microwaveprop.Geo do
   end
 
   @doc "Initial bearing from point 1 to point 2 in degrees (0-360)."
+  @spec bearing_deg(number(), number(), number(), number()) :: float()
   def bearing_deg(lat1, lon1, lat2, lon2) do
     lat1r = deg_to_rad(lat1)
     lat2r = deg_to_rad(lat2)
@@ -27,6 +29,7 @@ defmodule Microwaveprop.Geo do
   end
 
   @doc "Center of a 4-character Maidenhead grid square."
+  @spec maidenhead_center(String.t()) :: {float(), float()} | nil
   def maidenhead_center(grid) when is_binary(grid) and byte_size(grid) >= 4 do
     case Microwaveprop.Radio.Maidenhead.to_latlon(grid) do
       {:ok, {lat, lon}} -> {lat, lon}
@@ -35,6 +38,7 @@ defmodule Microwaveprop.Geo do
   end
 
   @doc "4-character Maidenhead grid for a lat/lon."
+  @spec latlon_to_grid4(number(), number()) :: String.t()
   def latlon_to_grid4(lat, lon) do
     lon_field = trunc((lon + 180) / 20)
     lat_field = trunc((lat + 90) / 10)
diff --git a/lib/microwaveprop/markdown.ex b/lib/microwaveprop/markdown.ex
index f44e538a..bb2d056a 100644
--- a/lib/microwaveprop/markdown.ex
+++ b/lib/microwaveprop/markdown.ex
@@ -7,6 +7,7 @@ defmodule Microwaveprop.Markdown do
   """
 
   @doc "Converts a Markdown string to HTML."
+  @spec to_html!(String.t()) :: String.t()
   def to_html!(markdown) do
     markdown
     |> String.replace("\r\n", "\n")
diff --git a/lib/microwaveprop/propagation.ex b/lib/microwaveprop/propagation.ex
index ec60bbac..e2c26bef 100644
--- a/lib/microwaveprop/propagation.ex
+++ b/lib/microwaveprop/propagation.ex
@@ -19,6 +19,7 @@ defmodule Microwaveprop.Propagation do
   Loads the ML model from disk, compiles the predict function, and caches both
   in persistent_term. No-op if the model file doesn't exist or ML deps unavailable.
   """
+  @spec load_ml_model() :: :ok
   def load_ml_model do
     if Code.ensure_loaded?(@ml_module) do
       case apply(@ml_module, :load, []) do
@@ -39,6 +40,7 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc "Returns cached {predict_fn, params} tuple, or nil if not loaded."
+  @spec ml_model() :: {function(), term()} | nil
   def ml_model do
     :persistent_term.get(@ml_key, nil)
   end
@@ -48,6 +50,8 @@ defmodule Microwaveprop.Propagation do
   Uses ML model if loaded, falls back to algorithm scorer.
   Returns a list of %{band_mhz, score, factors} maps.
   """
+  @spec score_grid_point(map(), DateTime.t(), float(), float()) ::
+          [%{band_mhz: non_neg_integer(), score: non_neg_integer(), factors: map()}]
   def score_grid_point(hrrr_profile, valid_time, latitude, longitude) do
     derived = derive_from_hrrr(hrrr_profile)
 
@@ -114,6 +118,7 @@ defmodule Microwaveprop.Propagation do
   Options:
     * `:prune` - whether to prune old scores after upsert (default true)
   """
+  @spec upsert_scores(Enumerable.t(), keyword()) :: {:ok, non_neg_integer()} | {:error, term()}
   def upsert_scores(scores, opts \\ []) do
     now = DateTime.truncate(DateTime.utc_now(), :second)
 
@@ -175,6 +180,7 @@ defmodule Microwaveprop.Propagation do
   timeout gives enough headroom for a catch-up run (potentially millions of
   rows across four indexes) after a stretch of failed compute jobs.
   """
+  @spec prune_old_scores() :: :ok
   def prune_old_scores do
     cutoff = DateTime.add(DateTime.utc_now(), -2, :hour)
 
@@ -191,6 +197,7 @@ defmodule Microwaveprop.Propagation do
   Filters out times more than 1 hour in the past, but always includes
   the most recent valid_time so there's always data to display.
   """
+  @spec available_valid_times(non_neg_integer()) :: [DateTime.t()]
   def available_valid_times(band_mhz) do
     cutoff = DateTime.add(DateTime.utc_now(), -3600, :second)
 
@@ -220,6 +227,8 @@ defmodule Microwaveprop.Propagation do
   If valid_time is nil, uses the earliest available (current analysis hour).
   Excludes factors for performance.
   """
+  @spec scores_at(non_neg_integer(), DateTime.t() | nil, map() | nil) ::
+          [%{lat: float(), lon: float(), score: non_neg_integer(), valid_time: DateTime.t()}]
   def scores_at(band_mhz, valid_time, bounds \\ nil) do
     time = valid_time || earliest_valid_time(band_mhz)
 
@@ -238,6 +247,8 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc "Get the latest scores for a band (alias for scores_at with earliest valid_time)."
+  @spec latest_scores(non_neg_integer(), map() | nil) ::
+          [%{lat: float(), lon: float(), score: non_neg_integer(), valid_time: DateTime.t()}]
   def latest_scores(band_mhz, bounds \\ nil) do
     scores_at(band_mhz, nil, bounds)
   end
@@ -247,6 +258,8 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc "Get scores across all forecast hours for a single grid point (for sparkline)."
+  @spec point_forecast(non_neg_integer(), float(), float()) ::
+          [%{valid_time: DateTime.t(), score: non_neg_integer()}]
   def point_forecast(band_mhz, lat, lon) do
     step = Grid.step()
     snapped_lat = Float.round(Float.round(lat / step) * step, 3)
@@ -267,6 +280,15 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc "Get the full score and factors for a specific grid point, snapped to nearest grid."
+  @spec point_detail(non_neg_integer(), float(), float(), DateTime.t() | nil) ::
+          %{
+            lat: float(),
+            lon: float(),
+            score: non_neg_integer(),
+            factors: map(),
+            valid_time: DateTime.t()
+          }
+          | nil
   def point_detail(band_mhz, lat, lon, valid_time \\ nil) do
     step = Grid.step()
     snapped_lat = Float.round(Float.round(lat / step) * step, 3)
@@ -307,11 +329,13 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc "Get the latest valid_time across all scores."
+  @spec latest_valid_time() :: DateTime.t() | nil
   def latest_valid_time do
     Repo.one(from(gs in GridScore, select: max(gs.valid_time)))
   end
 
   @doc "Get the latest valid_time for a specific band."
+  @spec latest_valid_time(non_neg_integer()) :: DateTime.t() | nil
   def latest_valid_time(band_mhz) do
     Repo.one(from(gs in GridScore, where: gs.band_mhz == ^band_mhz, select: max(gs.valid_time)))
   end
diff --git a/lib/microwaveprop/propagation/duct.ex b/lib/microwaveprop/propagation/duct.ex
index 8a9b984a..ede9e7dd 100644
--- a/lib/microwaveprop/propagation/duct.ex
+++ b/lib/microwaveprop/propagation/duct.ex
@@ -23,6 +23,7 @@ defmodule Microwaveprop.Propagation.Duct do
   Uses ITU-R P.453 with water vapor pressure derived from specific
   humidity.
   """
+  @spec refractivity_profile(map()) :: [{float(), float()}]
   def refractivity_profile(%{heights_m: heights, temp_k: temps, spfh: spfhs, pressure_pa: pressures}) do
     [heights, temps, spfhs, pressures]
     |> Enum.zip()
@@ -46,6 +47,7 @@ defmodule Microwaveprop.Propagation.Duct do
   In a standard atmosphere M always increases with height. A duct
   exists wherever M decreases.
   """
+  @spec m_profile([{float(), float()}]) :: [{float(), float()}]
   def m_profile(n_profile) do
     Enum.map(n_profile, fn {h, n} ->
       {h, n + 157.0 * h / 1000.0}
@@ -60,6 +62,8 @@ defmodule Microwaveprop.Propagation.Duct do
   where `m_deficit` is the total M decrease (positive number) across the
   duct — the strength of the trapping.
   """
+  @spec detect_ducts([{float(), float()}]) ::
+          [%{base_m: float(), top_m: float(), thickness_m: float(), m_deficit: float()}]
   def detect_ducts(m_profile) when length(m_profile) < 2, do: []
 
   def detect_ducts(m_profile) do
@@ -114,6 +118,7 @@ defmodule Microwaveprop.Propagation.Duct do
   where d is duct thickness in meters, ΔM is the M-deficit.
   Returns a very high frequency (999 GHz) for degenerate ducts.
   """
+  @spec min_trapped_frequency_ghz(%{thickness_m: float(), m_deficit: float()}) :: float()
   def min_trapped_frequency_ghz(%{thickness_m: d, m_deficit: delta_m}) when d > 0 and delta_m > 0 do
     # Maximum trapped wavelength (meters)
     lambda_max = 2.5 * d * :math.sqrt(delta_m * 1.0e-6)
@@ -135,6 +140,19 @@ defmodule Microwaveprop.Propagation.Duct do
   where each duct_map includes `:min_freq_ghz` and
   `best_duct_band_ghz` is the lowest min_freq across all detected ducts.
   """
+  @spec analyze(map()) ::
+          %{
+            ducts: [
+              %{
+                base_m: float(),
+                top_m: float(),
+                thickness_m: float(),
+                m_deficit: float(),
+                min_freq_ghz: float()
+              }
+            ],
+            best_duct_band_ghz: float() | nil
+          }
   def analyze(profile) do
     ducts =
       profile
diff --git a/lib/microwaveprop/propagation/freshness_monitor.ex b/lib/microwaveprop/propagation/freshness_monitor.ex
index 71df9917..91e08280 100644
--- a/lib/microwaveprop/propagation/freshness_monitor.ex
+++ b/lib/microwaveprop/propagation/freshness_monitor.ex
@@ -15,6 +15,7 @@ defmodule Microwaveprop.Propagation.FreshnessMonitor do
   @check_interval to_timeout(minute: 5)
   @stale_threshold_minutes 120
 
+  @spec start_link(keyword()) :: GenServer.on_start() | :ignore
   def start_link(_opts) do
     if Application.get_env(:microwaveprop, :start_freshness_monitor, true) do
       GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
diff --git a/lib/microwaveprop/propagation/grid.ex b/lib/microwaveprop/propagation/grid.ex
index 2cdaf652..a99766e1 100644
--- a/lib/microwaveprop/propagation/grid.ex
+++ b/lib/microwaveprop/propagation/grid.ex
@@ -8,6 +8,7 @@ defmodule Microwaveprop.Propagation.Grid do
   @step 0.125
 
   @doc "Returns all grid points as `{lat, lon}` tuples covering CONUS at 0.125 degree spacing."
+  @spec conus_points() :: [{float(), float()}]
   def conus_points do
     for lat <- float_range(@lat_min, @lat_max, @step),
         lon <- float_range(@lon_min, @lon_max, @step) do
@@ -16,12 +17,22 @@ defmodule Microwaveprop.Propagation.Grid do
   end
 
   @doc "Returns the grid step size in degrees."
+  @spec step() :: float()
   def step, do: @step
 
   @doc "Returns the CONUS bounding box as a map."
+  @spec bounds() :: %{lat_min: float(), lat_max: float(), lon_min: float(), lon_max: float()}
   def bounds, do: %{lat_min: @lat_min, lat_max: @lat_max, lon_min: @lon_min, lon_max: @lon_max}
 
   @doc "Returns the grid specification for wgrib2 -lola extraction."
+  @spec wgrib2_grid_spec() :: %{
+          lon_start: float(),
+          lon_count: non_neg_integer(),
+          lon_step: float(),
+          lat_start: float(),
+          lat_count: non_neg_integer(),
+          lat_step: float()
+        }
   def wgrib2_grid_spec do
     lon_count = round((@lon_max - @lon_min) / @step) + 1
     lat_count = round((@lat_max - @lat_min) / @step) + 1
diff --git a/lib/microwaveprop/propagation/grid_score.ex b/lib/microwaveprop/propagation/grid_score.ex
index a5adc6b5..46a9ffc2 100644
--- a/lib/microwaveprop/propagation/grid_score.ex
+++ b/lib/microwaveprop/propagation/grid_score.ex
@@ -17,8 +17,11 @@ defmodule Microwaveprop.Propagation.GridScore do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @fields ~w(lat lon valid_time band_mhz score factors)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(grid_score, attrs) do
     grid_score
     |> cast(attrs, @fields)
diff --git a/lib/microwaveprop/propagation/inversion.ex b/lib/microwaveprop/propagation/inversion.ex
index b6b159ce..5d103ff8 100644
--- a/lib/microwaveprop/propagation/inversion.ex
+++ b/lib/microwaveprop/propagation/inversion.ex
@@ -30,6 +30,15 @@ defmodule Microwaveprop.Propagation.Inversion do
 
   The profile map must have at least `:heights_m` and `:temp_k` arrays.
   """
+  @spec find_inversion_top(map()) ::
+          {:ok,
+           %{
+             height_m: float(),
+             level_idx: non_neg_integer(),
+             base_idx: non_neg_integer(),
+             strength_k: float()
+           }}
+          | :none
   def find_inversion_top(%{level_count: n}) when n < 2, do: :none
 
   def find_inversion_top(%{heights_m: heights, temp_k: temps}) do
@@ -100,6 +109,7 @@ defmodule Microwaveprop.Propagation.Inversion do
   Returns `nil` if inputs are missing or shear is zero (infinite Ri
   is clamped to 100.0 for practical use).
   """
+  @spec bulk_richardson(map(), non_neg_integer(), non_neg_integer()) :: float() | nil
   def bulk_richardson(profile, base_idx, top_idx) do
     with t_base when is_float(t_base) <- Enum.at(profile.temp_k, base_idx),
          t_top when is_float(t_top) <- Enum.at(profile.temp_k, top_idx),
@@ -134,6 +144,7 @@ defmodule Microwaveprop.Propagation.Inversion do
   @doc """
   Wind shear magnitude (m/s) across a layer from `base_idx` to `top_idx`.
   """
+  @spec shear_magnitude(map(), non_neg_integer(), non_neg_integer()) :: float() | nil
   def shear_magnitude(profile, base_idx, top_idx) do
     with u_base when is_float(u_base) <- Enum.at(profile.u_wind_ms, base_idx),
          u_top when is_float(u_top) <- Enum.at(profile.u_wind_ms, top_idx),
@@ -148,6 +159,7 @@ defmodule Microwaveprop.Propagation.Inversion do
   @doc """
   Potential temperature θ = T * (P₀/P)^(R/cp) where P₀ = 100000 Pa.
   """
+  @spec potential_temperature(float(), float()) :: float()
   def potential_temperature(temp_k, pressure_pa) do
     temp_k * :math.pow(100_000.0 / pressure_pa, 0.286)
   end
diff --git a/lib/microwaveprop/propagation/rain_scatter.ex b/lib/microwaveprop/propagation/rain_scatter.ex
index 510a7f54..9d31f836 100644
--- a/lib/microwaveprop/propagation/rain_scatter.ex
+++ b/lib/microwaveprop/propagation/rain_scatter.ex
@@ -33,6 +33,21 @@ defmodule Microwaveprop.Propagation.RainScatter do
   each with: lat, lon, dbz, distance_km, scatter_db (relative signal estimate),
   and bearing from the observer.
   """
+  @spec find_scatter_cells(
+          [{float(), float(), float()}],
+          float(),
+          float(),
+          float()
+        ) :: [
+          %{
+            lat: float(),
+            lon: float(),
+            dbz: float(),
+            distance_km: float(),
+            bearing: float(),
+            scatter_db: float()
+          }
+        ]
   def find_scatter_cells(rain_cells, obs_lat, obs_lon, freq_ghz) do
     rain_cells
     |> Enum.filter(fn {_lat, _lon, dbz} -> dbz >= @min_dbz end)
@@ -66,6 +81,7 @@ defmodule Microwaveprop.Propagation.RainScatter do
   Returns :excellent, :good, :marginal, or :none based on
   the best available scatter cell.
   """
+  @spec classify([%{scatter_db: float()}]) :: :excellent | :good | :marginal | :none
   def classify(scatter_cells) do
     case scatter_cells do
       [] ->
diff --git a/lib/microwaveprop/radio.ex b/lib/microwaveprop/radio.ex
index 6f5717ae..4bb1025b 100644
--- a/lib/microwaveprop/radio.ex
+++ b/lib/microwaveprop/radio.ex
@@ -3,6 +3,7 @@ defmodule Microwaveprop.Radio do
 
   import Ecto.Query
 
+  alias Microwaveprop.Accounts.User
   alias Microwaveprop.Radio.Contact
   alias Microwaveprop.Radio.ContactEdit
   alias Microwaveprop.Radio.Maidenhead
@@ -11,6 +12,15 @@ defmodule Microwaveprop.Radio do
   @per_page 20
   @sortable_fields ~w(station1 station2 band mode distance_km qso_timestamp inserted_at)a
 
+  @type contact_page :: %{
+          entries: [Contact.t()],
+          grouped_entries: [{Contact.t(), [Contact.t()]}],
+          page: pos_integer(),
+          total_pages: pos_integer(),
+          total_entries: non_neg_integer()
+        }
+
+  @spec list_contacts(keyword()) :: contact_page()
   def list_contacts(opts \\ []) do
     page = max(Keyword.get(opts, :page, 1), 1)
     offset = (page - 1) * @per_page
@@ -45,6 +55,7 @@ defmodule Microwaveprop.Radio do
   Returns a list of `{primary, reciprocals}` tuples where reciprocals is
   a (possibly empty) list of matching contacts.
   """
+  @spec group_reciprocals([Contact.t()]) :: [{Contact.t(), [Contact.t()]}]
   def group_reciprocals(contacts) do
     {groups, _seen_ids} =
       Enum.reduce(contacts, {[], MapSet.new()}, fn contact, {groups, seen} ->
@@ -118,6 +129,7 @@ defmodule Microwaveprop.Radio do
 
   @enrichable_statuses [:pending, :failed]
 
+  @spec contacts_needing_enrichment(atom(), non_neg_integer(), (Ecto.Query.t() -> Ecto.Query.t()) | nil) :: [Contact.t()]
   def contacts_needing_enrichment(field, limit \\ 500, extra_filter \\ nil) do
     query =
       Contact
@@ -129,30 +141,43 @@ defmodule Microwaveprop.Radio do
     Repo.all(query)
   end
 
+  @spec unprocessed_contacts(non_neg_integer()) :: [Contact.t()]
   def unprocessed_contacts(limit \\ 500), do: contacts_needing_enrichment(:weather_status, limit)
 
+  @spec unprocessed_hrrr_contacts(non_neg_integer()) :: [Contact.t()]
   def unprocessed_hrrr_contacts(limit \\ 500), do: contacts_needing_enrichment(:hrrr_status, limit)
 
+  @spec unprocessed_terrain_contacts(non_neg_integer()) :: [Contact.t()]
   def unprocessed_terrain_contacts(limit \\ 500),
     do: contacts_needing_enrichment(:terrain_status, limit, &where(&1, [q], not is_nil(q.pos2)))
 
+  @spec unprocessed_iemre_contacts(non_neg_integer()) :: [Contact.t()]
   def unprocessed_iemre_contacts(limit \\ 500), do: contacts_needing_enrichment(:iemre_status, limit)
 
+  @spec set_enrichment_status!([Ecto.UUID.t()], atom(), atom()) :: {non_neg_integer(), nil | [any()]}
   def set_enrichment_status!(ids, field, status) do
     Contact
     |> where([q], q.id in ^ids and field(q, ^field) != ^status)
     |> Repo.update_all(set: [{field, status}])
   end
 
+  @spec mark_weather_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
   def mark_weather_queued!(ids), do: set_enrichment_status!(ids, :weather_status, :queued)
+
+  @spec mark_hrrr_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
   def mark_hrrr_queued!(ids), do: set_enrichment_status!(ids, :hrrr_status, :queued)
+
+  @spec mark_terrain_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
   def mark_terrain_queued!(ids), do: set_enrichment_status!(ids, :terrain_status, :queued)
+
+  @spec mark_iemre_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
   def mark_iemre_queued!(ids), do: set_enrichment_status!(ids, :iemre_status, :queued)
 
   @doc """
   Returns a list of {lat, lon} points along the contact path: pos1, midpoint, pos2.
   Returns [pos1] if pos2 is nil, or [] if pos1 is nil.
   """
+  @spec contact_path_points(Contact.t()) :: [{float(), float()}]
   def contact_path_points(%{pos1: nil}), do: []
 
   def contact_path_points(%{pos1: pos1, pos2: nil}) do
@@ -183,6 +208,7 @@ defmodule Microwaveprop.Radio do
 
   @earth_radius_km 6371.0
 
+  @spec haversine_km(number(), number(), number(), number()) :: float()
   def haversine_km(lat1, lon1, lat2, lon2) do
     dlat = deg_to_rad(lat2 - lat1)
     dlon = deg_to_rad(lon2 - lon1)
@@ -196,6 +222,7 @@ defmodule Microwaveprop.Radio do
     2 * @earth_radius_km * :math.asin(:math.sqrt(a))
   end
 
+  @spec backfill_distances([Contact.t()]) :: Postgrex.Result.t() | nil
   def backfill_distances(contacts) do
     updates =
       for contact <- contacts,
@@ -230,16 +257,19 @@ defmodule Microwaveprop.Radio do
 
   defp deg_to_rad(deg), do: deg * :math.pi() / 180
 
+  @spec get_contact!(Ecto.UUID.t()) :: Contact.t()
   def get_contact!(id) do
     Repo.get!(Contact, id)
   end
 
+  @spec toggle_flagged_invalid!(Contact.t()) :: Contact.t()
   def toggle_flagged_invalid!(contact) do
     contact
     |> Ecto.Changeset.change(flagged_invalid: !contact.flagged_invalid)
     |> Repo.update!()
   end
 
+  @spec change_contact(Contact.t(), map()) :: Ecto.Changeset.t()
   def change_contact(contact, attrs \\ %{}) do
     Contact.submission_changeset(contact, attrs)
   end
@@ -248,6 +278,7 @@ defmodule Microwaveprop.Radio do
   Computes pos1/pos2/distance_km from grid squares if missing.
   Returns the updated contact, or the original if already computed or grids are missing.
   """
+  @spec ensure_positions!(Contact.t()) :: Contact.t()
   def ensure_positions!(contact) do
     needs_pos1 = is_nil(contact.pos1) && contact.grid1
     needs_pos2 = is_nil(contact.pos2) && contact.grid2
@@ -331,6 +362,8 @@ defmodule Microwaveprop.Radio do
 
   @dedup_window_seconds 3600
 
+  @spec create_contact(map()) ::
+          {:ok, Contact.t()} | {:error, Ecto.Changeset.t()} | {:error, :duplicate, Contact.t()}
   def create_contact(attrs) do
     changeset = Contact.submission_changeset(%Contact{}, attrs)
 
@@ -402,6 +435,8 @@ defmodule Microwaveprop.Radio do
   differ from the contact's current values. Normalizes callsigns and grids
   to uppercase.
   """
+  @spec create_contact_edit(Contact.t(), User.t(), map()) ::
+          {:ok, ContactEdit.t()} | {:error, Ecto.Changeset.t()}
   def create_contact_edit(%Contact{} = contact, user, proposed_changes) when is_map(proposed_changes) do
     # Normalize and diff against current values
     normalized = normalize_proposed(proposed_changes)
@@ -419,6 +454,7 @@ defmodule Microwaveprop.Radio do
   end
 
   @doc false
+  @spec normalize_proposed(map()) :: map()
   def normalize_proposed(changes) do
     changes
     |> normalize_string_field("station1")
@@ -437,6 +473,7 @@ defmodule Microwaveprop.Radio do
   end
 
   @doc false
+  @spec diff_against_contact(Contact.t(), map()) :: map()
   def diff_against_contact(contact, proposed) do
     Enum.reduce(proposed, %{}, fn {key, new_val}, acc ->
       current = current_value(contact, key)
@@ -475,6 +512,7 @@ defmodule Microwaveprop.Radio do
   defp to_integer(%Decimal{} = v), do: Decimal.to_integer(v)
   defp to_integer(v), do: v
 
+  @spec list_pending_edits() :: [ContactEdit.t()]
   def list_pending_edits do
     ContactEdit
     |> where([e], e.status == :pending)
@@ -483,6 +521,7 @@ defmodule Microwaveprop.Radio do
     |> Repo.all()
   end
 
+  @spec list_contact_edits(Ecto.UUID.t()) :: [ContactEdit.t()]
   def list_contact_edits(contact_id) do
     ContactEdit
     |> where([e], e.contact_id == ^contact_id)
@@ -491,24 +530,29 @@ defmodule Microwaveprop.Radio do
     |> Repo.all()
   end
 
+  @spec pending_edit_count() :: non_neg_integer()
   def pending_edit_count do
     ContactEdit
     |> where([e], e.status == :pending)
     |> Repo.aggregate(:count)
   end
 
+  @spec pending_edit_for_user(Ecto.UUID.t(), Ecto.UUID.t()) :: ContactEdit.t() | nil
   def pending_edit_for_user(contact_id, user_id) do
     ContactEdit
     |> where([e], e.contact_id == ^contact_id and e.user_id == ^user_id and e.status == :pending)
     |> Repo.one()
   end
 
+  @spec get_contact_edit!(Ecto.UUID.t()) :: ContactEdit.t()
   def get_contact_edit!(id) do
     ContactEdit
     |> preload([:user, :contact, :reviewed_by])
     |> Repo.get!(id)
   end
 
+  @spec approve_edit(ContactEdit.t(), User.t(), String.t() | nil) ::
+          {:ok, ContactEdit.t()} | {:error, any()}
   def approve_edit(%ContactEdit{status: :pending} = edit, admin, note) do
     Repo.transaction(fn ->
       # Mark edit as approved
@@ -530,6 +574,8 @@ defmodule Microwaveprop.Radio do
     end)
   end
 
+  @spec reject_edit(ContactEdit.t(), User.t(), String.t() | nil) ::
+          {:ok, ContactEdit.t()} | {:error, Ecto.Changeset.t()}
   def reject_edit(%ContactEdit{status: :pending} = edit, admin, note) do
     edit
     |> ContactEdit.review_changeset(%{
@@ -542,6 +588,7 @@ defmodule Microwaveprop.Radio do
   end
 
   @doc "Apply proposed changes directly to a contact (admin use)."
+  @spec apply_edit_to_contact(Contact.t(), map()) :: Contact.t()
   def apply_edit_to_contact(contact, proposed_changes) do
     changes = build_contact_changes(contact, proposed_changes)
 
diff --git a/lib/microwaveprop/radio/adif_import.ex b/lib/microwaveprop/radio/adif_import.ex
index e3f1cca0..fb5b0cc9 100644
--- a/lib/microwaveprop/radio/adif_import.ex
+++ b/lib/microwaveprop/radio/adif_import.ex
@@ -36,6 +36,15 @@ defmodule Microwaveprop.Radio.AdifImport do
   Parse ADIF string, validate, and deduplicate. Returns the same preview
   shape as `CsvImport.preview/2`.
   """
+  @type preview_result :: %{
+          valid: [map()],
+          invalid: [map()],
+          duplicates: [map()],
+          total_rows: non_neg_integer(),
+          submitter_email: String.t()
+        }
+
+  @spec preview(String.t(), String.t()) :: {:ok, preview_result()} | {:error, :no_records}
   def preview(adif_string, submitter_email) do
     records = parse_adif(adif_string)
 
diff --git a/lib/microwaveprop/radio/callsign_client.ex b/lib/microwaveprop/radio/callsign_client.ex
index da4a0481..dadd089e 100644
--- a/lib/microwaveprop/radio/callsign_client.ex
+++ b/lib/microwaveprop/radio/callsign_client.ex
@@ -4,6 +4,14 @@ defmodule Microwaveprop.Radio.CallsignClient do
   @doc """
   Fetch location for a callsign. Returns {:ok, %{callsign, gridsquare, lat, lon}} or {:error, reason}.
   """
+  @type location :: %{
+          callsign: String.t(),
+          gridsquare: String.t() | nil,
+          lat: number(),
+          lon: number()
+        }
+
+  @spec locate(String.t()) :: {:ok, location()} | {:error, String.t()}
   def locate(callsign) do
     url = "https://gridmap.org/locate/#{URI.encode(callsign)}"
 
diff --git a/lib/microwaveprop/radio/contact.ex b/lib/microwaveprop/radio/contact.ex
index 87050aaa..801905e0 100644
--- a/lib/microwaveprop/radio/contact.ex
+++ b/lib/microwaveprop/radio/contact.ex
@@ -47,9 +47,12 @@ defmodule Microwaveprop.Radio.Contact do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(station1 station2 qso_timestamp mode band)a
   @optional_fields ~w(grid1 grid2 pos1 pos2 distance_km user_id)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(contact, attrs) do
     contact
     |> cast(attrs, @required_fields ++ @optional_fields)
@@ -61,6 +64,7 @@ defmodule Microwaveprop.Radio.Contact do
   @allowed_modes ~w(CW SSB FM FT8 FT4 Q65)
   @allowed_bands Enum.map(~w(1296 2304 3456 5760 10000 24000 47000 68000 75000 122000 134000 241000), &Decimal.new/1)
 
+  @spec submission_changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def submission_changeset(contact, attrs) do
     contact
     |> cast(attrs, @submission_fields)
diff --git a/lib/microwaveprop/radio/contact_edit.ex b/lib/microwaveprop/radio/contact_edit.ex
index 85c98073..796a2576 100644
--- a/lib/microwaveprop/radio/contact_edit.ex
+++ b/lib/microwaveprop/radio/contact_edit.ex
@@ -27,8 +27,11 @@ defmodule Microwaveprop.Radio.ContactEdit do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @editable_fields ~w(station1 station2 grid1 grid2 band mode qso_timestamp)
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(edit, attrs) do
     edit
     |> cast(attrs, [:contact_id, :user_id, :proposed_changes])
@@ -38,6 +41,7 @@ defmodule Microwaveprop.Radio.ContactEdit do
     |> foreign_key_constraint(:user_id)
   end
 
+  @spec review_changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def review_changeset(edit, attrs) do
     edit
     |> cast(attrs, [:status, :admin_note, :reviewed_by_id, :reviewed_at])
diff --git a/lib/microwaveprop/radio/csv_import.ex b/lib/microwaveprop/radio/csv_import.ex
index 65333223..2b01b900 100644
--- a/lib/microwaveprop/radio/csv_import.ex
+++ b/lib/microwaveprop/radio/csv_import.ex
@@ -36,6 +36,26 @@ defmodule Microwaveprop.Radio.CsvImport do
   Parse-and-insert in one shot. Kept for backward compatibility — does NOT
   perform duplicate detection. New code should use `preview/2` + `commit/1`.
   """
+  @type preview_result :: %{
+          valid: [map()],
+          invalid: [map()],
+          duplicates: [map()],
+          total_rows: non_neg_integer(),
+          submitter_email: String.t()
+        }
+
+  @type import_result :: %{
+          imported: [Contact.t()],
+          errors: [{pos_integer(), [String.t()]}]
+        }
+
+  @type commit_result :: %{
+          imported: [Contact.t()],
+          errors: [{pos_integer(), [String.t()]}]
+        }
+
+  @spec import(String.t(), String.t()) ::
+          {:ok, import_result()} | {:error, :empty_csv} | {:error, :no_data_rows}
   def import(csv_string, submitter_email) do
     with {:ok, rows} <- parse_csv(csv_string, submitter_email) do
       {valid, invalid} = split_parsed(rows)
@@ -66,6 +86,8 @@ defmodule Microwaveprop.Radio.CsvImport do
   the database (`:existing_contact`) or earlier in the uploaded file
   (`:earlier_in_upload`).
   """
+  @spec preview(String.t(), String.t()) ::
+          {:ok, preview_result()} | {:error, :empty_csv} | {:error, :no_data_rows}
   def preview(csv_string, submitter_email) do
     with {:ok, rows} <- parse_csv(csv_string, submitter_email) do
       {valid, invalid} = split_parsed(rows)
@@ -88,6 +110,7 @@ defmodule Microwaveprop.Radio.CsvImport do
   `Radio.create_contact/1` and its enrichment is enqueued on success.
   Returns `{:ok, %{imported: [...], errors: [{row_num, messages}, ...]}}`.
   """
+  @spec commit([map()]) :: {:ok, commit_result()}
   def commit(valid_rows) when is_list(valid_rows) do
     result =
       Enum.reduce(valid_rows, %{imported: [], errors: []}, fn row, acc ->
@@ -313,6 +336,7 @@ defmodule Microwaveprop.Radio.CsvImport do
   Parses various date/time formats into ISO 8601 UTC strings.
   All times are assumed UTC.
   """
+  @spec normalize_timestamp(String.t()) :: {:ok, String.t()} | {:error, String.t()}
   def normalize_timestamp(raw) do
     trimmed = String.trim(raw)
 
diff --git a/lib/microwaveprop/radio/enrichment_status.ex b/lib/microwaveprop/radio/enrichment_status.ex
index ee063c21..2d0ea581 100644
--- a/lib/microwaveprop/radio/enrichment_status.ex
+++ b/lib/microwaveprop/radio/enrichment_status.ex
@@ -19,6 +19,9 @@ defmodule Microwaveprop.Radio.EnrichmentStatus do
     complete    → pending (reset for re-enrichment)
   """
 
+  @type status :: :pending | :queued | :processing | :complete | :failed | :unavailable
+  @type field_name :: :hrrr_status | :weather_status | :terrain_status | :iemre_status
+
   @states [:pending, :queued, :processing, :complete, :failed, :unavailable]
   @fields [:hrrr_status, :weather_status, :terrain_status, :iemre_status]
 
@@ -31,15 +34,20 @@ defmodule Microwaveprop.Radio.EnrichmentStatus do
     complete: [:pending]
   }
 
+  @spec states() :: [status()]
   def states, do: @states
+
+  @spec fields() :: [field_name()]
   def fields, do: @fields
 
   @doc "Returns true if transitioning from `from` to `to` is valid."
+  @spec valid_transition?(status(), status()) :: boolean()
   def valid_transition?(from, to) do
     to in Map.get(@transitions, from, [])
   end
 
   @doc "Validates and applies a status transition on a changeset."
+  @spec transition(Ecto.Changeset.t(), field_name(), status()) :: Ecto.Changeset.t()
   def transition(changeset, field, new_status) when field in @fields and new_status in @states do
     current = Ecto.Changeset.get_field(changeset, field)
 
@@ -51,6 +59,7 @@ defmodule Microwaveprop.Radio.EnrichmentStatus do
   end
 
   @doc "Force-sets status without transition validation (for migrations, resets)."
+  @spec force_status(Ecto.Changeset.t(), field_name(), status()) :: Ecto.Changeset.t()
   def force_status(changeset, field, status) when field in @fields and status in @states do
     Ecto.Changeset.put_change(changeset, field, status)
   end
diff --git a/lib/microwaveprop/terrain.ex b/lib/microwaveprop/terrain.ex
index 18af37ac..e53c4a8f 100644
--- a/lib/microwaveprop/terrain.ex
+++ b/lib/microwaveprop/terrain.ex
@@ -6,6 +6,7 @@ defmodule Microwaveprop.Terrain do
   alias Microwaveprop.Repo
   alias Microwaveprop.Terrain.TerrainProfile
 
+  @spec upsert_terrain_profile(map()) :: {:ok, TerrainProfile.t()} | {:error, Ecto.Changeset.t()}
   def upsert_terrain_profile(attrs) do
     %TerrainProfile{}
     |> TerrainProfile.changeset(attrs)
@@ -15,10 +16,12 @@ defmodule Microwaveprop.Terrain do
     )
   end
 
+  @spec get_terrain_profile(Ecto.UUID.t()) :: TerrainProfile.t() | nil
   def get_terrain_profile(contact_id) do
     Repo.get_by(TerrainProfile, contact_id: contact_id)
   end
 
+  @spec has_terrain_profile?(Ecto.UUID.t()) :: boolean()
   def has_terrain_profile?(contact_id) do
     TerrainProfile
     |> where([t], t.contact_id == ^contact_id)
diff --git a/lib/microwaveprop/terrain/terrain_analysis.ex b/lib/microwaveprop/terrain/terrain_analysis.ex
index f281a0fc..37ad9a0b 100644
--- a/lib/microwaveprop/terrain/terrain_analysis.ex
+++ b/lib/microwaveprop/terrain/terrain_analysis.ex
@@ -8,6 +8,38 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
   - Dynamic k-factor from refractivity gradient (Section 2)
   """
 
+  @type elevation_point :: %{lat: float(), lon: float(), elev: float(), d: float(), dist_km: float()}
+
+  @type analysis_point :: %{
+          lat: float(),
+          lon: float(),
+          d: float(),
+          elev: float(),
+          dist_km: float(),
+          idx: non_neg_integer(),
+          beam: float(),
+          eff_terrain: float(),
+          bulge: float(),
+          r1: float(),
+          d1_m: float(),
+          d2_m: float(),
+          clearance: float(),
+          f1_clear: float(),
+          obstructed: boolean(),
+          fresnel_penetrated: boolean()
+        }
+
+  @type analysis_result :: %{
+          points: [analysis_point()],
+          diffraction_db: number(),
+          verdict: String.t(),
+          k_factor: float(),
+          max_elevation_m: float(),
+          min_clearance_m: float(),
+          obstructed_count: non_neg_integer(),
+          fresnel_hit_count: non_neg_integer()
+        }
+
   @earth_radius_m 6_371_000.0
   @earth_radius_km 6_371.0
 
@@ -20,6 +52,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
     * `:ant_ht_b` - antenna height B in meters (default 0.0)
     * `:k_factor` - effective earth radius factor (default 4/3, compute with `k_factor/1`)
   """
+  @spec analyse([elevation_point()], float(), float(), keyword()) :: analysis_result()
   def analyse(profile, dist_km, freq_ghz, opts \\ []) do
     ant_ht_a = Keyword.get(opts, :ant_ht_a, 0.0)
     ant_ht_b = Keyword.get(opts, :ant_ht_b, 0.0)
@@ -98,6 +131,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
   end
 
   @doc "First Fresnel zone radius at a point between two antennas."
+  @spec fresnel_radius(number(), number(), number()) :: number()
   def fresnel_radius(d1_m, d2_m, lambda_m) do
     if d1_m <= 0 or d2_m <= 0 do
       0
@@ -107,6 +141,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
   end
 
   @doc "Earth bulge correction in meters at fractional distance along path."
+  @spec earth_bulge(float(), float(), float()) :: float()
   def earth_bulge(frac, dist_km, k \\ 4 / 3) do
     d1 = frac * dist_km * 1000
     d2 = (1 - frac) * dist_km * 1000
@@ -119,6 +154,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
   J(ν) = 6.9 + 20·log10(√((ν−0.1)² + 1) + ν − 0.1)  for ν > −0.78
   J(ν) = 0                                                for ν ≤ −0.78
   """
+  @spec knife_edge_loss(number()) :: number()
   def knife_edge_loss(v) when v <= -0.78, do: 0
 
   def knife_edge_loss(v) do
@@ -133,6 +169,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
 
   where h is height above direct ray (positive = above/blocked, negative = below/clear).
   """
+  @spec diffraction_param(number(), number(), number(), number()) :: float()
   def diffraction_param(h, d1_m, d2_m, lambda_m) do
     if d1_m <= 0 or d2_m <= 0 or lambda_m <= 0 do
       0.0
@@ -149,6 +186,7 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
   Standard atmosphere: dN/dh ≈ −39 → k ≈ 4/3.
   Returns 4/3 for nil input.
   """
+  @spec k_factor(number() | nil) :: float()
   def k_factor(nil), do: 4 / 3
 
   def k_factor(dn_dh) do
diff --git a/lib/microwaveprop/terrain/terrain_profile.ex b/lib/microwaveprop/terrain/terrain_profile.ex
index 5373ec4b..a7e5b3cb 100644
--- a/lib/microwaveprop/terrain/terrain_profile.ex
+++ b/lib/microwaveprop/terrain/terrain_profile.ex
@@ -21,9 +21,12 @@ defmodule Microwaveprop.Terrain.TerrainProfile do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(contact_id sample_count path_points verdict)a
   @optional_fields ~w(max_elevation_m min_clearance_m diffraction_db fresnel_hit_count obstructed_count)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(profile, attrs) do
     profile
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/terrain/viewshed.ex b/lib/microwaveprop/terrain/viewshed.ex
index a07f77d1..492342d0 100644
--- a/lib/microwaveprop/terrain/viewshed.ex
+++ b/lib/microwaveprop/terrain/viewshed.ex
@@ -4,11 +4,19 @@ defmodule Microwaveprop.Terrain.Viewshed do
   alias Microwaveprop.Terrain.Srtm
   alias Microwaveprop.Terrain.TerrainAnalysis
 
+  @type boundary_point :: %{bearing: non_neg_integer(), reach_km: float(), lat: float(), lon: float()}
+
+  @type viewshed_result :: %{
+          origin: %{lat: float(), lon: float()},
+          boundary: [boundary_point()]
+        }
+
   @earth_radius_km 6371.0
   @default_angular_step 2
   @default_max_range_km 50
 
   @doc "Compute destination lat/lon given origin, bearing (degrees), and distance (km)."
+  @spec destination_point(float(), float(), float(), float()) :: {float(), float()}
   def destination_point(lat, lon, bearing_deg, dist_km) do
     lat_rad = deg_to_rad(lat)
     lon_rad = deg_to_rad(lon)
@@ -36,6 +44,7 @@ defmodule Microwaveprop.Terrain.Viewshed do
   Skips endpoints (first/last), returns the dist_km of the last clear
   interior point before the first obstruction.
   """
+  @spec find_reach_km([TerrainAnalysis.analysis_point()], float()) :: float()
   def find_reach_km(points, max_range_km) do
     interior = Enum.slice(points, 1..-2//1)
 
@@ -56,6 +65,7 @@ defmodule Microwaveprop.Terrain.Viewshed do
   Higher propagation scores indicate ducting potential, which lets signals
   propagate beyond terrain obstructions via atmospheric waveguide.
   """
+  @spec effective_reach_km(TerrainAnalysis.analysis_result(), float(), number()) :: float()
   def effective_reach_km(analysis, max_range_km, score) do
     case analysis.verdict do
       "CLEAR" ->
@@ -104,6 +114,7 @@ defmodule Microwaveprop.Terrain.Viewshed do
     - :angular_step — degrees between rays (default 2)
     - :tiles_dir — SRTM tiles directory (default from config)
   """
+  @spec compute(float(), float(), keyword()) :: viewshed_result()
   def compute(lat, lon, opts \\ []) do
     freq_ghz = Keyword.get(opts, :freq_ghz, 10.0)
     max_range_km = Keyword.get(opts, :max_range_km, @default_max_range_km)
@@ -138,6 +149,8 @@ defmodule Microwaveprop.Terrain.Viewshed do
   Analyse a single ray's profile. Public for testing.
   Returns %{reach_km: float, verdict: string}.
   """
+  @spec analyse_ray([TerrainAnalysis.elevation_point()], float(), float(), float(), float()) ::
+          %{reach_km: float(), verdict: String.t()}
   def analyse_ray(profile, dist_km, freq_ghz, ant_ht_a_m, ant_ht_b_m) do
     analysis = TerrainAnalysis.analyse(profile, dist_km, freq_ghz, ant_ht_a: ant_ht_a_m, ant_ht_b: ant_ht_b_m)
     reach_km = find_reach_km(analysis.points, dist_km)
diff --git a/lib/microwaveprop/weather.ex b/lib/microwaveprop/weather.ex
index 45e029b7..c8c5c4f3 100644
--- a/lib/microwaveprop/weather.ex
+++ b/lib/microwaveprop/weather.ex
@@ -21,6 +21,7 @@ defmodule Microwaveprop.Weather do
   # Approximate km per degree latitude
   @km_per_deg_lat 111.0
 
+  @spec find_or_create_station(map()) :: {:ok, %Station{}} | {:error, Ecto.Changeset.t()}
   def find_or_create_station(attrs) do
     code = attrs[:station_code] || attrs["station_code"]
     type = attrs[:station_type] || attrs["station_type"]
@@ -42,6 +43,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec upsert_surface_observation(%Station{}, map()) :: {:ok, %SurfaceObservation{}} | {:error, Ecto.Changeset.t()}
   def upsert_surface_observation(%Station{} = station, attrs) do
     attrs = Map.put(attrs, :station_id, station.id)
 
@@ -76,6 +78,7 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec upsert_sounding(%Station{}, map()) :: {:ok, %Sounding{}} | {:error, Ecto.Changeset.t()}
   def upsert_sounding(%Station{} = station, attrs) do
     attrs = Map.put(attrs, :station_id, station.id)
 
@@ -113,6 +116,7 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec upsert_solar_index(map()) :: {:ok, %SolarIndex{}} | {:error, Ecto.Changeset.t()}
   def upsert_solar_index(attrs) do
     %SolarIndex{}
     |> SolarIndex.changeset(attrs)
@@ -139,6 +143,7 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec has_surface_observations?(Ecto.UUID.t(), DateTime.t(), DateTime.t()) :: boolean()
   def has_surface_observations?(station_id, start_dt, end_dt) do
     SurfaceObservation
     |> where([o], o.station_id == ^station_id)
@@ -147,6 +152,7 @@ defmodule Microwaveprop.Weather do
   end
 
   @doc "Returns a MapSet of station_ids that have surface observations in the time window."
+  @spec station_ids_with_surface_observations([Ecto.UUID.t()], DateTime.t(), DateTime.t()) :: MapSet.t(Ecto.UUID.t())
   def station_ids_with_surface_observations(station_ids, start_dt, end_dt) do
     SurfaceObservation
     |> where([o], o.station_id in ^station_ids)
@@ -157,6 +163,7 @@ defmodule Microwaveprop.Weather do
     |> MapSet.new()
   end
 
+  @spec has_sounding?(Ecto.UUID.t(), DateTime.t()) :: boolean()
   def has_sounding?(station_id, observed_at) do
     Sounding
     |> where([s], s.station_id == ^station_id and s.observed_at == ^observed_at)
@@ -164,6 +171,7 @@ defmodule Microwaveprop.Weather do
   end
 
   @doc "Returns a MapSet of {station_id, observed_at} tuples that have soundings."
+  @spec station_ids_with_soundings([Ecto.UUID.t()], [DateTime.t()]) :: MapSet.t({Ecto.UUID.t(), DateTime.t()})
   def station_ids_with_soundings(station_ids, sounding_times) do
     Sounding
     |> where([s], s.station_id in ^station_ids and s.observed_at in ^sounding_times)
@@ -174,6 +182,7 @@ defmodule Microwaveprop.Weather do
   end
 
   @doc "Batch upsert solar indices using insert_all in chunks of 500."
+  @spec upsert_solar_indices_batch([map()]) :: non_neg_integer()
   def upsert_solar_indices_batch(records) do
     now = DateTime.truncate(DateTime.utc_now(), :second)
 
@@ -220,10 +229,12 @@ defmodule Microwaveprop.Weather do
     end)
   end
 
+  @spec get_solar_index(Date.t()) :: %SolarIndex{} | nil
   def get_solar_index(date) do
     Repo.get_by(SolarIndex, date: date)
   end
 
+  @spec existing_solar_dates() :: MapSet.t(Date.t())
   def existing_solar_dates do
     SolarIndex
     |> select([s], s.date)
@@ -231,6 +242,7 @@ defmodule Microwaveprop.Weather do
     |> MapSet.new()
   end
 
+  @spec sync_stations!() :: :ok
   def sync_stations! do
     asos =
       for s <-
@@ -262,6 +274,7 @@ defmodule Microwaveprop.Weather do
     :ok
   end
 
+  @spec nearby_stations(float(), float(), String.t(), number()) :: [%Station{}]
   def nearby_stations(lat, lon, station_type, radius_km) do
     dlat = radius_km / @km_per_deg_lat
     dlon = radius_km / (@km_per_deg_lat * :math.cos(lat * :math.pi() / 180))
@@ -276,6 +289,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.all()
   end
 
+  @spec sounding_times_around(DateTime.t()) :: [DateTime.t()]
   def sounding_times_around(dt) do
     date = DateTime.to_date(dt)
 
@@ -295,6 +309,10 @@ defmodule Microwaveprop.Weather do
     Enum.uniq(times)
   end
 
+  @spec weather_for_contact(map(), keyword()) :: %{
+          surface_observations: [%SurfaceObservation{}],
+          soundings: [%Sounding{}]
+        }
   def weather_for_contact(contact_params, opts \\ []) do
     lat = contact_params[:lat] || contact_params.lat
     lon = contact_params[:lon] || contact_params.lon
@@ -336,6 +354,7 @@ defmodule Microwaveprop.Weather do
     %{surface_observations: surface_observations, soundings: soundings}
   end
 
+  @spec latest_grid_valid_time() :: DateTime.t() | nil
   def latest_grid_valid_time do
     Repo.one(
       from(h in HrrrProfile,
@@ -345,6 +364,7 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec latest_weather_grid(map()) :: [map()]
   def latest_weather_grid(bounds) do
     case latest_grid_valid_time() do
       nil ->
@@ -380,6 +400,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec weather_point_detail(float(), float(), DateTime.t()) :: map() | nil
   def weather_point_detail(lat, lon, valid_time) do
     step = 0.125
     snapped_lat = Float.round(Float.round(lat / step) * step, 3)
@@ -420,6 +441,7 @@ defmodule Microwaveprop.Weather do
     |> Map.drop([:profile, :duct_characteristics, :surface_temp_c, :surface_dewpoint_c])
   end
 
+  @spec upsert_hrrr_profile(map()) :: {:ok, %HrrrProfile{}} | {:error, Ecto.Changeset.t()}
   def upsert_hrrr_profile(attrs) do
     %HrrrProfile{}
     |> HrrrProfile.changeset(attrs)
@@ -429,6 +451,7 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec upsert_hrrr_profiles_batch([map()], keyword()) :: {non_neg_integer(), nil}
   def upsert_hrrr_profiles_batch(profiles, _opts \\ []) do
     now = DateTime.truncate(DateTime.utc_now(), :second)
 
@@ -459,6 +482,7 @@ defmodule Microwaveprop.Weather do
     end)
   end
 
+  @spec has_hrrr_profile?(float(), float(), DateTime.t()) :: boolean()
   def has_hrrr_profile?(lat, lon, valid_time) do
     dlat = 0.07
     dlon = 0.07
@@ -473,6 +497,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.exists?()
   end
 
+  @spec hrrr_for_contact(map()) :: %HrrrProfile{} | nil
   def hrrr_for_contact(%{pos1: nil}), do: nil
 
   def hrrr_for_contact(contact) do
@@ -484,6 +509,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec find_nearest_hrrr(float(), float(), DateTime.t()) :: %HrrrProfile{} | nil
   def find_nearest_hrrr(lat, lon, timestamp) do
     dlat = 0.07
     dlon = 0.07
@@ -513,6 +539,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.one()
   end
 
+  @spec hrrr_profiles_for_path(map()) :: [%HrrrProfile{}]
   def hrrr_profiles_for_path(%{pos1: nil}), do: []
 
   def hrrr_profiles_for_path(contact) do
@@ -527,11 +554,13 @@ defmodule Microwaveprop.Weather do
   Tries HRRR first (3 km, hourly), falls back to ERA5 (0.25°, hourly).
   Returns the profile struct or nil.
   """
+  @spec best_profile_for_contact(map()) :: %HrrrProfile{} | %Era5Profile{} | nil
   def best_profile_for_contact(contact) do
     hrrr_for_contact(contact) || era5_for_contact(contact)
   end
 
   @doc "Find all atmospheric profiles along a contact's path, from any source."
+  @spec profiles_along_path(map()) :: [%HrrrProfile{} | %Era5Profile{}]
   def profiles_along_path(contact) do
     hrrr_path = hrrr_profiles_for_path(contact)
 
@@ -542,6 +571,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec era5_for_contact(map()) :: %Era5Profile{} | nil
   def era5_for_contact(%{pos1: nil}), do: nil
 
   def era5_for_contact(contact) do
@@ -553,6 +583,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec era5_profiles_for_path(map()) :: [%Era5Profile{}]
   def era5_profiles_for_path(%{pos1: nil}), do: []
 
   def era5_profiles_for_path(contact) do
@@ -562,6 +593,7 @@ defmodule Microwaveprop.Weather do
     |> Enum.reject(&is_nil/1)
   end
 
+  @spec find_nearest_era5(float(), float(), DateTime.t()) :: %Era5Profile{} | nil
   def find_nearest_era5(lat, lon, timestamp) do
     dlat = 0.15
     dlon = 0.15
@@ -589,6 +621,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.one()
   end
 
+  @spec find_nearest_rtma(float(), float(), DateTime.t()) :: %RtmaObservation{} | nil
   def find_nearest_rtma(lat, lon, timestamp) do
     dlat = 0.05
     dlon = 0.05
@@ -618,6 +651,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.one()
   end
 
+  @spec round_to_hrrr_grid(float(), float()) :: {float(), float()}
   def round_to_hrrr_grid(lat, lon) do
     {Float.round(lat / 1.0, 2), Float.round(lon / 1.0, 2)}
   end
@@ -627,6 +661,7 @@ defmodule Microwaveprop.Weather do
   Preserves QSO-linked profiles which are at arbitrary lat/lon positions.
   With 19 forecast hours per run, this keeps ~2 runs worth of grid profiles.
   """
+  @spec prune_old_grid_profiles() :: non_neg_integer()
   def prune_old_grid_profiles do
     cutoff = DateTime.add(DateTime.utc_now(), -24, :hour)
     # Bound the scan to recent partitions only (grid profiles are at most ~48h old).
@@ -655,10 +690,12 @@ defmodule Microwaveprop.Weather do
     deleted
   end
 
+  @spec round_to_iemre_grid(float(), float()) :: {float(), float()}
   def round_to_iemre_grid(lat, lon) do
     {Float.round(lat * 8) / 8, Float.round(lon * 8) / 8}
   end
 
+  @spec upsert_iemre_observation(map()) :: {:ok, %IemreObservation{}} | {:error, Ecto.Changeset.t()}
   def upsert_iemre_observation(attrs) do
     %IemreObservation{}
     |> IemreObservation.changeset(attrs)
@@ -668,12 +705,14 @@ defmodule Microwaveprop.Weather do
     )
   end
 
+  @spec has_iemre_observation?(float(), float(), Date.t()) :: boolean()
   def has_iemre_observation?(lat, lon, date) do
     IemreObservation
     |> where([i], i.lat == ^lat and i.lon == ^lon and i.date == ^date)
     |> Repo.exists?()
   end
 
+  @spec iemre_for_contact(map()) :: %IemreObservation{} | nil
   def iemre_for_contact(%{pos1: nil}), do: nil
 
   def iemre_for_contact(contact) do
@@ -685,6 +724,7 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @spec find_nearest_iemre(float(), float(), DateTime.t()) :: %IemreObservation{} | nil
   def find_nearest_iemre(lat, lon, timestamp) do
     {rlat, rlon} = round_to_iemre_grid(lat, lon)
     date = DateTime.to_date(timestamp)
@@ -694,6 +734,7 @@ defmodule Microwaveprop.Weather do
     |> Repo.one()
   end
 
+  @spec iemre_for_path(map()) :: [%IemreObservation{}]
   def iemre_for_path(%{pos1: nil}), do: []
 
   def iemre_for_path(contact) do
@@ -712,6 +753,7 @@ defmodule Microwaveprop.Weather do
   `:observed_at`, etc. — the same shape regardless of which table the
   data came from. Returns `nil` if neither source has data.
   """
+  @spec recent_surface_obs(float(), float(), DateTime.t()) :: %Metar5minObservation{} | %SurfaceObservation{} | nil
   def recent_surface_obs(lat, lon, timestamp) do
     dlat = 0.5
     dlon = 0.5
diff --git a/lib/microwaveprop/weather/era5_batch_client.ex b/lib/microwaveprop/weather/era5_batch_client.ex
index 12febd7b..eb713d3a 100644
--- a/lib/microwaveprop/weather/era5_batch_client.ex
+++ b/lib/microwaveprop/weather/era5_batch_client.ex
@@ -37,6 +37,7 @@ defmodule Microwaveprop.Weather.Era5BatchClient do
   Returns the integer tile coordinate `{tile_lat, tile_lon}` for a point,
   where `tile_lat` is the south edge and `tile_lon` is the west edge.
   """
+  @spec tile_for_point(float(), float()) :: {integer(), integer()}
   def tile_for_point(lat, lon) do
     {floor_to_tile(lat), floor_to_tile(lon)}
   end
@@ -50,6 +51,7 @@ defmodule Microwaveprop.Weather.Era5BatchClient do
   end
 
   @doc false
+  @spec tile_degrees() :: pos_integer()
   def tile_degrees, do: @tile_degrees
 
   @doc """
@@ -57,6 +59,12 @@ defmodule Microwaveprop.Weather.Era5BatchClient do
   resulting hourly profile in `era5_profiles`. Returns
   `{:ok, inserted_count}` or `{:error, reason}`.
   """
+  @spec fetch_month_into_db(%{
+          year: pos_integer(),
+          month: pos_integer(),
+          tile_lat: integer(),
+          tile_lon: integer()
+        }) :: {:ok, non_neg_integer()} | {:error, term()}
   def fetch_month_into_db(%{year: year, month: month, tile_lat: tile_lat, tile_lon: tile_lon}) do
     if month_tile_cached?(year, month, tile_lat, tile_lon) do
       Logger.info("ERA5Batch: #{year}-#{pad(month)} tile #{tile_lat},#{tile_lon} already cached")
diff --git a/lib/microwaveprop/weather/era5_client.ex b/lib/microwaveprop/weather/era5_client.ex
index 94c4fcfe..7e3ef0e4 100644
--- a/lib/microwaveprop/weather/era5_client.ex
+++ b/lib/microwaveprop/weather/era5_client.ex
@@ -32,16 +32,22 @@ defmodule Microwaveprop.Weather.Era5Client do
   @pressure_level_vars ~w(temperature dewpoint_temperature geopotential)
 
   @doc false
+  @spec pressure_levels() :: [String.t()]
   def pressure_levels, do: @pressure_levels
   @doc false
+  @spec single_level_vars() :: [String.t()]
   def single_level_vars, do: @single_level_vars
   @doc false
+  @spec pressure_level_vars() :: [String.t()]
   def pressure_level_vars, do: @pressure_level_vars
   @doc false
+  @spec cds_url() :: String.t()
   def cds_url, do: @cds_url
   @doc false
+  @spec poll_interval_ms() :: pos_integer()
   def poll_interval_ms, do: @poll_interval_ms
   @doc false
+  @spec max_poll_attempts() :: pos_integer()
   def max_poll_attempts, do: @max_poll_attempts
 
   @doc """
@@ -50,6 +56,7 @@ defmodule Microwaveprop.Weather.Era5Client do
 
   The profile_attrs map has the same shape as HRRR profiles for interoperability.
   """
+  @spec fetch_profile(float(), float(), DateTime.t()) :: {:ok, map()} | {:error, term()}
   def fetch_profile(lat, lon, timestamp) do
     # Round to ERA5 grid (0.25°)
     rlat = Float.round(lat * 4) / 4
@@ -71,6 +78,7 @@ defmodule Microwaveprop.Weather.Era5Client do
   @doc """
   Fetch ERA5 single-level (surface) data for a time and area.
   """
+  @spec fetch_single_levels(DateTime.t(), [number()]) :: {:ok, binary()} | {:error, term()}
   def fetch_single_levels(valid_time, area) do
     request = %{
       "product_type" => ["reanalysis"],
@@ -89,6 +97,7 @@ defmodule Microwaveprop.Weather.Era5Client do
   @doc """
   Fetch ERA5 pressure-level data for a time and area.
   """
+  @spec fetch_pressure_levels(DateTime.t(), [number()]) :: {:ok, binary()} | {:error, term()}
   def fetch_pressure_levels(valid_time, area) do
     request = %{
       "product_type" => ["reanalysis"],
@@ -106,6 +115,7 @@ defmodule Microwaveprop.Weather.Era5Client do
   end
 
   @doc false
+  @spec submit_and_download(String.t(), map()) :: {:ok, binary()} | {:error, term()}
   def submit_and_download(dataset, request) do
     do_submit_and_download(dataset, request)
   end
diff --git a/lib/microwaveprop/weather/era5_profile.ex b/lib/microwaveprop/weather/era5_profile.ex
index e7681dff..35c56ee0 100644
--- a/lib/microwaveprop/weather/era5_profile.ex
+++ b/lib/microwaveprop/weather/era5_profile.ex
@@ -25,9 +25,12 @@ defmodule Microwaveprop.Weather.Era5Profile do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(valid_time lat lon)a
   @optional_fields ~w(profile hpbl_m pwat_mm surface_temp_c surface_dewpoint_c surface_pressure_mb surface_refractivity min_refractivity_gradient ducting_detected duct_characteristics)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(profile, attrs) do
     profile
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/frontal_analysis.ex b/lib/microwaveprop/weather/frontal_analysis.ex
index ef9307de..dd255161 100644
--- a/lib/microwaveprop/weather/frontal_analysis.ex
+++ b/lib/microwaveprop/weather/frontal_analysis.ex
@@ -40,6 +40,12 @@ defmodule Microwaveprop.Weather.FrontalAnalysis do
   where `front_points` is a list of the strongest frontal pixels
   for easy lookup.
   """
+  @spec detect_fronts(Nx.Tensor.t(), Nx.Tensor.t(), map()) :: %{
+          tfp: Nx.Tensor.t(),
+          mask: Nx.Tensor.t(),
+          bearing_deg: Nx.Tensor.t(),
+          front_points: [{float(), float(), float()}]
+        }
   def detect_fronts(temp_grid, pressure_grid, grid_spec) do
     # Potential temperature: θ = T * (100000/P)^0.286
     theta = Nx.multiply(temp_grid, Nx.pow(Nx.divide(100_000.0, pressure_grid), 0.286))
@@ -88,6 +94,8 @@ defmodule Microwaveprop.Weather.FrontalAnalysis do
   @doc """
   Compute distance (km) and angle to the nearest front point from a given lat/lon.
   """
+  @spec nearest_front([{float(), float(), float()}], float(), float()) ::
+          %{distance_km: float(), front_bearing_deg: float(), front_lat: float(), front_lon: float()} | nil
   def nearest_front(front_points, lat, lon) when is_list(front_points) do
     if front_points == [] do
       nil
@@ -116,6 +124,7 @@ defmodule Microwaveprop.Weather.FrontalAnalysis do
   @doc """
   Angle between a QSO path and the nearest front (0° = parallel, 90° = crosses).
   """
+  @spec path_front_angle(float(), float()) :: float()
   def path_front_angle(path_bearing_deg, front_bearing_deg) do
     diff = abs(path_bearing_deg - front_bearing_deg)
     diff = if diff > 180, do: 360 - diff, else: diff
diff --git a/lib/microwaveprop/weather/grib2/complex_packing.ex b/lib/microwaveprop/weather/grib2/complex_packing.ex
index 85eb386e..2d71d639 100644
--- a/lib/microwaveprop/weather/grib2/complex_packing.ex
+++ b/lib/microwaveprop/weather/grib2/complex_packing.ex
@@ -8,6 +8,7 @@ defmodule Microwaveprop.Weather.Grib2.ComplexPacking do
   Decodes all values since spatial differencing requires sequential access,
   then returns the value at the target index.
   """
+  @spec extract_value(map(), binary(), non_neg_integer()) :: {:ok, float()} | {:error, term()}
   def extract_value(params, data, index) do
     if index < 0 or index >= params.num_data_points do
       {:error, :index_out_of_range}
@@ -27,6 +28,8 @@ defmodule Microwaveprop.Weather.Grib2.ComplexPacking do
 
   Returns `{:ok, %{index => value}}`.
   """
+  @spec extract_values(map(), binary(), [non_neg_integer()]) ::
+          {:ok, %{non_neg_integer() => float()}} | {:error, term()}
   def extract_values(params, data, indices) do
     case decode_all(params, data) do
       {:ok, array} ->
@@ -43,6 +46,7 @@ defmodule Microwaveprop.Weather.Grib2.ComplexPacking do
 
   Returns an Erlang array of floats for O(1) index access.
   """
+  @spec decode_all(map(), binary()) :: {:ok, :array.array(float())} | {:error, String.t()}
   def decode_all(params, data) do
     %{
       reference_value: ref,
diff --git a/lib/microwaveprop/weather/grib2/extractor.ex b/lib/microwaveprop/weather/grib2/extractor.ex
index b0a9b3e8..bd0a265a 100644
--- a/lib/microwaveprop/weather/grib2/extractor.ex
+++ b/lib/microwaveprop/weather/grib2/extractor.ex
@@ -11,6 +11,7 @@ defmodule Microwaveprop.Weather.Grib2.Extractor do
 
   Returns `{:ok, %{"VAR:LEVEL" => float}}` or `{:error, term}`.
   """
+  @spec extract_points(binary(), float(), float()) :: {:ok, %{String.t() => float()}} | {:error, term()}
   def extract_points(binary, lat, lon) do
     messages = split_messages(binary)
 
@@ -33,6 +34,8 @@ defmodule Microwaveprop.Weather.Grib2.Extractor do
   Takes a binary and a list of `{lat, lon}` tuples.
   Returns `{:ok, %{{lat, lon} => %{"VAR:LEVEL" => float}}}` or `{:error, term}`.
   """
+  @spec extract_grid(binary(), [{float(), float()}]) ::
+          {:ok, %{{float(), float()} => %{String.t() => float()}}} | {:error, term()}
   def extract_grid(binary, points) do
     messages = split_messages(binary)
 
@@ -83,6 +86,7 @@ defmodule Microwaveprop.Weather.Grib2.Extractor do
   Split a binary blob into individual GRIB2 messages by scanning for "GRIB" magic bytes
   and reading the total length from the indicator section.
   """
+  @spec split_messages(binary()) :: [binary()]
   def split_messages(binary), do: split_messages(binary, [])
 
   @doc """
@@ -90,6 +94,8 @@ defmodule Microwaveprop.Weather.Grib2.Extractor do
 
   For HRRR scan_mode=64 (j positive, i positive, i consecutive): index = j * nx + i
   """
+  @spec linear_index({non_neg_integer(), non_neg_integer()}, pos_integer(), non_neg_integer()) ::
+          non_neg_integer()
   def linear_index({i, j}, nx, _scan_mode) do
     j * nx + i
   end
diff --git a/lib/microwaveprop/weather/grib2/lambert_conformal.ex b/lib/microwaveprop/weather/grib2/lambert_conformal.ex
index 633ad995..7f48c68f 100644
--- a/lib/microwaveprop/weather/grib2/lambert_conformal.ex
+++ b/lib/microwaveprop/weather/grib2/lambert_conformal.ex
@@ -8,6 +8,8 @@ defmodule Microwaveprop.Weather.Grib2.LambertConformal do
 
   Returns `{:ok, {i, j}}` or `{:error, :outside_grid}`.
   """
+  @spec to_grid_index(map(), float(), float()) ::
+          {:ok, {non_neg_integer(), non_neg_integer()}} | {:error, :outside_grid}
   def to_grid_index(grid, lat, lon) do
     %{
       nx: nx,
diff --git a/lib/microwaveprop/weather/grib2/section.ex b/lib/microwaveprop/weather/grib2/section.ex
index 11171cef..96e35718 100644
--- a/lib/microwaveprop/weather/grib2/section.ex
+++ b/lib/microwaveprop/weather/grib2/section.ex
@@ -6,6 +6,16 @@ defmodule Microwaveprop.Weather.Grib2.Section do
 
   Returns `{:ok, %{grid_params, product, packing_params, data, bitmap}}`.
   """
+  @spec parse_message(binary()) ::
+          {:ok,
+           %{
+             grid_params: map(),
+             product: %{var: String.t(), level: String.t()},
+             packing_params: map(),
+             data: binary(),
+             bitmap: :none | :present
+           }}
+          | {:error, String.t()}
   def parse_message(<<"GRIB", _reserved::16, _discipline::8, 2::8, total_length::64-big, rest::binary>> = msg) do
     discipline = :binary.at(msg, 6)
     # Skip indicator section (16 bytes), parse remaining sections
@@ -22,6 +32,7 @@ defmodule Microwaveprop.Weather.Grib2.Section do
   @doc """
   Identify variable name from discipline, parameter category, and parameter number.
   """
+  @spec identify_var(non_neg_integer(), non_neg_integer(), non_neg_integer()) :: String.t()
   def identify_var(0, 0, 0), do: "TMP"
   def identify_var(0, 0, 6), do: "DPT"
   def identify_var(0, 3, 0), do: "PRES"
@@ -39,6 +50,7 @@ defmodule Microwaveprop.Weather.Grib2.Section do
   @doc """
   Identify level string from surface type and scaled value.
   """
+  @spec identify_level(non_neg_integer(), non_neg_integer()) :: String.t()
   def identify_level(1, _value), do: "surface"
   def identify_level(100, value_pa), do: "#{div(value_pa, 100)} mb"
   def identify_level(103, value_m), do: "#{value_m} m above ground"
@@ -52,6 +64,7 @@ defmodule Microwaveprop.Weather.Grib2.Section do
   @doc """
   Decode a 16-bit sign-magnitude integer.
   """
+  @spec sign_magnitude_16(<<_::16>>) :: integer()
   def sign_magnitude_16(<<0::1, value::15>>), do: value
   def sign_magnitude_16(<<1::1, value::15>>), do: -value
 
diff --git a/lib/microwaveprop/weather/grib2/simple_packing.ex b/lib/microwaveprop/weather/grib2/simple_packing.ex
index fa197d2d..505794f5 100644
--- a/lib/microwaveprop/weather/grib2/simple_packing.ex
+++ b/lib/microwaveprop/weather/grib2/simple_packing.ex
@@ -9,6 +9,7 @@ defmodule Microwaveprop.Weather.Grib2.SimplePacking do
   Where R = reference_value, E = binary_scale, D = decimal_scale,
   X = raw packed integer at the given index.
   """
+  @spec extract_value(map(), binary(), non_neg_integer()) :: {:ok, float()} | {:error, :index_out_of_range}
   def extract_value(%{bits_per_value: 0} = params, _data, _index) do
     {:ok, params.reference_value * :math.pow(10, -params.decimal_scale)}
   end
@@ -36,6 +37,7 @@ defmodule Microwaveprop.Weather.Grib2.SimplePacking do
 
   Returns `{:ok, %{index => value}}`. Out-of-range indices are silently skipped.
   """
+  @spec extract_values(map(), binary(), [non_neg_integer()]) :: {:ok, %{non_neg_integer() => float()}}
   def extract_values(%{bits_per_value: 0} = params, _data, indices) do
     value = params.reference_value * :math.pow(10, -params.decimal_scale)
     {:ok, Map.new(indices, fn i -> {i, value} end)}
diff --git a/lib/microwaveprop/weather/grib2/wgrib2.ex b/lib/microwaveprop/weather/grib2/wgrib2.ex
index e1d8af4d..572d8c12 100644
--- a/lib/microwaveprop/weather/grib2/wgrib2.ex
+++ b/lib/microwaveprop/weather/grib2/wgrib2.ex
@@ -9,6 +9,17 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
 
   require Logger
 
+  @typep grid_spec :: %{
+           lon_start: float(),
+           lon_count: pos_integer(),
+           lon_step: float(),
+           lat_start: float(),
+           lat_count: pos_integer(),
+           lat_step: float()
+         }
+
+  @typep point_grid :: %{{float(), float()} => %{String.t() => float()}}
+
   @undefined_value 9.999e20
 
   @doc """
@@ -19,6 +30,7 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
 
   Returns `{:ok, %{{lat, lon} => %{"VAR:LEVEL" => float}}}` or `{:error, reason}`.
   """
+  @spec extract_grid(binary(), String.t(), grid_spec()) :: {:ok, point_grid()} | {:error, term()}
   def extract_grid(grib_binary, match_pattern, grid_spec) do
     if available?() do
       extract_with_wgrib2(grib_binary, match_pattern, grid_spec)
@@ -32,6 +44,8 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
   of a binary. Avoids loading the entire file into memory — useful for
   large native-level HRRR files (~530 MB).
   """
+  @spec extract_grid_from_file(Path.t(), String.t(), grid_spec()) ::
+          {:ok, point_grid()} | {:error, term()}
   def extract_grid_from_file(grib_path, match_pattern, grid_spec) do
     if available?() do
       extract_file_with_wgrib2(grib_path, match_pattern, grid_spec)
@@ -52,6 +66,12 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
   Peak memory: binary output (~76 MB for 200 msgs × 95k cells) + one
   cell's worth of data at a time + output map (~10 MB of scalars).
   """
+  @spec extract_grid_from_file_mapped(
+          Path.t(),
+          String.t(),
+          grid_spec(),
+          (%{String.t() => float()} -> term())
+        ) :: {:ok, %{{float(), float()} => term()}} | {:error, term()}
   def extract_grid_from_file_mapped(grib_path, match_pattern, grid_spec, cell_reducer) do
     if available?() do
       extract_file_mapped_with_wgrib2(grib_path, match_pattern, grid_spec, cell_reducer)
@@ -61,6 +81,7 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
   end
 
   @doc "Check if wgrib2 is available on the system."
+  @spec available?() :: boolean()
   def available?, do: wgrib2_path() != nil
 
   defp wgrib2_path, do: System.find_executable("wgrib2")
@@ -312,6 +333,17 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
   Each entry is `%{datetime: DateTime.t() | nil, var: String.t(),
   level: String.t(), values: %{{lat, lon} => float}}`.
   """
+  @spec extract_grid_messages(binary(), String.t(), grid_spec()) ::
+          {:ok,
+           [
+             %{
+               datetime: DateTime.t() | nil,
+               var: String.t(),
+               level: String.t(),
+               values: %{{float(), float()} => float()}
+             }
+           ]}
+          | {:error, term()}
   def extract_grid_messages(grib_binary, match_pattern, grid_spec) do
     if available?() do
       extract_messages_with_wgrib2(grib_binary, match_pattern, grid_spec)
@@ -475,6 +507,8 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
 
   Returns `{:ok, %{{lat, lon} => %{"VAR:LEVEL" => float}}}` or `{:error, reason}`.
   """
+  @spec extract_points_from_file(Path.t(), String.t(), [{float(), float()}]) ::
+          {:ok, point_grid()} | {:error, term()}
   def extract_points_from_file(grib_path, match_pattern, points) when is_list(points) do
     if available?() do
       extract_points_with_wgrib2(grib_path, match_pattern, points)
diff --git a/lib/microwaveprop/weather/hrrr_client.ex b/lib/microwaveprop/weather/hrrr_client.ex
index 8de3e9c0..d5463dd6 100644
--- a/lib/microwaveprop/weather/hrrr_client.ex
+++ b/lib/microwaveprop/weather/hrrr_client.ex
@@ -43,8 +43,11 @@ defmodule Microwaveprop.Weather.HrrrClient do
 
   # --- Public API ---
 
+  @spec surface_messages() :: [%{var: String.t(), level: String.t()}]
   def surface_messages, do: @surface_messages
 
+  @spec fetch_grid([{float(), float()}], DateTime.t(), keyword()) ::
+          {:ok, %{{float(), float()} => map()}} | {:error, term()}
   def fetch_grid(points, run_time, opts \\ []) do
     hour_dt = nearest_hrrr_hour(run_time)
     date = DateTime.to_date(hour_dt)
@@ -77,6 +80,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end
   end
 
+  @spec fetch_profile(float(), float(), DateTime.t()) :: {:ok, map()} | {:error, term()}
   def fetch_profile(lat, lon, valid_time) do
     hour_dt = nearest_hrrr_hour(valid_time)
     date = DateTime.to_date(hour_dt)
@@ -103,6 +107,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end
   end
 
+  @spec nearest_hrrr_hour(DateTime.t()) :: DateTime.t()
   def nearest_hrrr_hour(dt) do
     total_seconds = dt.minute * 60 + dt.second
     rounded_dt = DateTime.add(dt, -total_seconds, :second)
@@ -114,6 +119,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end
   end
 
+  @spec hrrr_url(Date.t(), non_neg_integer(), :surface | :pressure, non_neg_integer()) :: String.t()
   def hrrr_url(date, hour, product, forecast_hour \\ 0) do
     date_str = Calendar.strftime(date, "%Y%m%d")
     hour_str = hour |> Integer.to_string() |> String.pad_leading(2, "0")
@@ -128,6 +134,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     "#{hrrr_base()}/hrrr.#{date_str}/conus/#{file}"
   end
 
+  @spec parse_idx(String.t()) :: [%{msg: integer(), offset: integer(), var: String.t(), level: String.t()}]
   def parse_idx(text) do
     text
     |> String.split("\n")
@@ -144,6 +151,9 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end)
   end
 
+  @spec byte_ranges_for_messages([map()], [%{var: String.t(), level: String.t()}]) :: [
+          {non_neg_integer(), non_neg_integer()}
+        ]
   def byte_ranges_for_messages(idx_entries, wanted) do
     Enum.flat_map(wanted, fn w ->
       idx_entries
@@ -164,12 +174,14 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end)
   end
 
+  @spec merge_grid_data(map(), map()) :: map()
   def merge_grid_data(sfc_grid, prs_grid) do
     Map.merge(sfc_grid, prs_grid, fn _point, sfc_data, prs_data ->
       Map.merge(sfc_data, prs_data)
     end)
   end
 
+  @spec build_profile(map()) :: map()
   def build_profile(parsed) do
     sfc_temp_k = parsed["TMP:2 m above ground"]
     sfc_dpt_k = parsed["DPT:2 m above ground"]
@@ -319,6 +331,8 @@ defmodule Microwaveprop.Weather.HrrrClient do
   Public so the native-level client can reuse it rather than
   duplicating the HTTP/parallelism/cache logic.
   """
+  @spec download_grib_ranges(String.t(), [{non_neg_integer(), non_neg_integer()}]) ::
+          {:ok, binary()} | {:error, term()}
   def download_grib_ranges(_url, []), do: {:ok, <<>>}
 
   def download_grib_ranges(url, ranges) do
@@ -349,6 +363,8 @@ defmodule Microwaveprop.Weather.HrrrClient do
 
   Returns `:ok` or `{:error, reason}`.
   """
+  @spec download_grib_ranges_to_file(String.t(), [{non_neg_integer(), non_neg_integer()}], Path.t()) ::
+          :ok | {:error, term()}
   def download_grib_ranges_to_file(_url, [], _dest_path), do: :ok
 
   def download_grib_ranges_to_file(url, ranges, dest_path) do
diff --git a/lib/microwaveprop/weather/hrrr_climatology.ex b/lib/microwaveprop/weather/hrrr_climatology.ex
index e3b8ed95..9cae7949 100644
--- a/lib/microwaveprop/weather/hrrr_climatology.ex
+++ b/lib/microwaveprop/weather/hrrr_climatology.ex
@@ -27,6 +27,7 @@ defmodule Microwaveprop.Weather.HrrrClimatology do
     field :sample_count, :integer
   end
 
+  @spec changeset(%__MODULE__{}, map()) :: Ecto.Changeset.t()
   def changeset(record, attrs) do
     record
     |> cast(attrs, [:lat, :lon, :month, :hour, :mean_surface_temp_c, :stddev_surface_temp_c, :sample_count])
diff --git a/lib/microwaveprop/weather/hrrr_native_client.ex b/lib/microwaveprop/weather/hrrr_native_client.ex
index 8d087f4d..b3efd94a 100644
--- a/lib/microwaveprop/weather/hrrr_native_client.ex
+++ b/lib/microwaveprop/weather/hrrr_native_client.ex
@@ -34,9 +34,11 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   defp hrrr_base, do: Application.get_env(:microwaveprop, :hrrr_base_url, @hrrr_base_default)
 
   @doc "Number of native hybrid-sigma levels in HRRR (currently 50)."
+  @spec native_level_count() :: pos_integer()
   def native_level_count, do: Enum.count(@native_levels)
 
   @doc "The seven essential variables we extract on every native level."
+  @spec native_variables() :: [String.t()]
   def native_variables, do: @native_variables
 
   @doc """
@@ -44,6 +46,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   file. 7 vars × 50 levels = 350 messages, matching the spike in
   Task 1.1.
   """
+  @spec native_messages() :: [%{var: String.t(), level: String.t()}]
   def native_messages do
     for level <- @native_levels, var <- @native_variables do
       %{var: var, level: "#{level} hybrid level"}
@@ -58,6 +61,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
       iex> Microwaveprop.Weather.HrrrNativeClient.hrrr_native_url(~D[2026-04-09], 12)
       "https://noaa-hrrr-bdp-pds.s3.amazonaws.com/hrrr.20260409/conus/hrrr.t12z.wrfnatf00.grib2"
   """
+  @spec hrrr_native_url(Date.t(), non_neg_integer(), non_neg_integer()) :: String.t()
   def hrrr_native_url(date, hour, forecast_hour \\ 0) do
     date_str = Calendar.strftime(date, "%Y%m%d")
     hour_str = hour |> Integer.to_string() |> String.pad_leading(2, "0")
@@ -75,6 +79,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   lets us unit-test every invariant we care about (array lengths,
   ordering, surface scalar caching) without touching the network.
   """
+  @spec build_native_profile(map()) :: map()
   def build_native_profile(parsed) when is_map(parsed) do
     levels =
       @native_levels
@@ -121,6 +126,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   Wraps `HrrrClient.byte_ranges_for_messages/2` with our native
   message list so callers don't have to know both.
   """
+  @spec essential_byte_ranges([map()]) :: [{non_neg_integer(), non_neg_integer()}]
   def essential_byte_ranges(idx_entries) do
     HrrrClient.byte_ranges_for_messages(idx_entries, native_messages())
   end
@@ -133,6 +139,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   Messages needed for duct detection only (4 vars × 50 levels = 200 messages).
   ~300 MB download vs ~530 MB for all 7 variables.
   """
+  @spec duct_messages() :: [%{var: String.t(), level: String.t()}]
   def duct_messages do
     for level <- @native_levels, var <- @duct_variables do
       %{var: var, level: "#{level} hybrid level"}
@@ -142,6 +149,7 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   @doc """
   Byte ranges for duct-detection variables only.
   """
+  @spec duct_byte_ranges([map()]) :: [{non_neg_integer(), non_neg_integer()}]
   def duct_byte_ranges(idx_entries) do
     HrrrClient.byte_ranges_for_messages(idx_entries, duct_messages())
   end
@@ -155,6 +163,8 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
 
   Returns `{:ok, %{{lat, lon} => duct_metrics}}` or `{:error, reason}`.
   """
+  @spec fetch_native_duct_grid(Date.t(), non_neg_integer(), map(), non_neg_integer()) ::
+          {:ok, %{{float(), float()} => map()}} | {:error, term()}
   def fetch_native_duct_grid(date, hour, grid_spec, forecast_hour \\ 0) do
     alias Microwaveprop.Weather.Grib2.Wgrib2
 
@@ -252,6 +262,8 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
 
   Returns `{:ok, %{{lat, lon} => native_profile_map}}` or `{:error, reason}`.
   """
+  @spec extract_native_profiles_from_file(Path.t(), [{float(), float()}]) ::
+          {:ok, %{{float(), float()} => map()}} | {:error, term()}
   def extract_native_profiles_from_file(grib_path, points) when is_list(points) do
     alias Microwaveprop.Weather.Grib2.Wgrib2
 
@@ -289,6 +301,8 @@ defmodule Microwaveprop.Weather.HrrrNativeClient do
   Returns `%{{lat, lon} => native_profile_map}` where each profile
   map has the shape expected by `HrrrNativeProfile.changeset/2`.
   """
+  @spec extract_native_profiles(binary(), [{float(), float()}]) ::
+          {:ok, %{{float(), float()} => map()}} | {:error, term()}
   def extract_native_profiles(grib_binary, points) when is_list(points) do
     alias Microwaveprop.Weather.Grib2.Wgrib2
 
diff --git a/lib/microwaveprop/weather/hrrr_native_profile.ex b/lib/microwaveprop/weather/hrrr_native_profile.ex
index 1bd0b20d..f52e7eb3 100644
--- a/lib/microwaveprop/weather/hrrr_native_profile.ex
+++ b/lib/microwaveprop/weather/hrrr_native_profile.ex
@@ -54,6 +54,8 @@ defmodule Microwaveprop.Weather.HrrrNativeProfile do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required ~w(valid_time lat lon)a
   @optional ~w(
     run_time level_count heights_m temp_k spfh pressure_pa
@@ -63,6 +65,7 @@ defmodule Microwaveprop.Weather.HrrrNativeProfile do
     ducts best_duct_band_ghz
   )a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(profile, attrs) do
     profile
     |> cast(attrs, @required ++ @optional)
diff --git a/lib/microwaveprop/weather/hrrr_profile.ex b/lib/microwaveprop/weather/hrrr_profile.ex
index cfb05b28..a9feb195 100644
--- a/lib/microwaveprop/weather/hrrr_profile.ex
+++ b/lib/microwaveprop/weather/hrrr_profile.ex
@@ -27,9 +27,12 @@ defmodule Microwaveprop.Weather.HrrrProfile do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(valid_time lat lon)a
   @optional_fields ~w(run_time profile hpbl_m pwat_mm surface_temp_c surface_dewpoint_c surface_pressure_mb surface_refractivity min_refractivity_gradient ducting_detected duct_characteristics is_grid_point)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(hrrr_profile, attrs) do
     hrrr_profile
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/iem_client.ex b/lib/microwaveprop/weather/iem_client.ex
index 0c6f2a01..120d2791 100644
--- a/lib/microwaveprop/weather/iem_client.ex
+++ b/lib/microwaveprop/weather/iem_client.ex
@@ -5,10 +5,12 @@ defmodule Microwaveprop.Weather.IemClient do
 
   # --- URL builders ---
 
+  @spec network_url(String.t()) :: String.t()
   def network_url(network) do
     "#{@iem_base}/json/network.py?network=#{network}"
   end
 
+  @spec asos_url(String.t(), DateTime.t(), DateTime.t()) :: String.t()
   def asos_url(station_id, start_dt, end_dt) do
     "#{@iem_base}/cgi-bin/request/asos.py" <>
       "?station=#{station_id}" <>
@@ -21,17 +23,20 @@ defmodule Microwaveprop.Weather.IemClient do
       "&format=onlycomma&latlon=no&elev=no&missing=null&trace=null&direct=no&report_type=3"
   end
 
+  @spec raob_url(String.t(), DateTime.t()) :: String.t()
   def raob_url(station_id, dt) do
     ts = format_iem_ts(dt)
     "#{@iem_base}/json/raob.py?ts=#{ts}&station=#{station_id}"
   end
 
+  @spec iemre_url(float(), float(), Date.t()) :: String.t()
   def iemre_url(lat, lon, date) do
     "#{@iem_base}/iemre/hourly/#{date}/#{lat}/#{lon}/json"
   end
 
   # --- HTTP fetchers ---
 
+  @spec fetch_network(String.t()) :: {:ok, [map()]} | {:error, term()}
   def fetch_network(network) do
     url = network_url(network)
 
@@ -47,6 +52,7 @@ defmodule Microwaveprop.Weather.IemClient do
     end
   end
 
+  @spec fetch_asos(String.t(), DateTime.t(), DateTime.t()) :: {:ok, [map()]} | {:error, term()}
   def fetch_asos(station_id, start_dt, end_dt) do
     url = asos_url(station_id, start_dt, end_dt)
 
@@ -62,6 +68,7 @@ defmodule Microwaveprop.Weather.IemClient do
     end
   end
 
+  @spec fetch_raob(String.t(), DateTime.t()) :: {:ok, [map()]} | {:error, term()}
   def fetch_raob(station_id, dt) do
     url = raob_url(station_id, dt)
 
@@ -77,6 +84,7 @@ defmodule Microwaveprop.Weather.IemClient do
     end
   end
 
+  @spec fetch_iemre(float(), float(), Date.t()) :: {:ok, [map()]} | {:error, term()}
   def fetch_iemre(lat, lon, date) do
     url = iemre_url(lat, lon, date)
 
@@ -116,6 +124,7 @@ defmodule Microwaveprop.Weather.IemClient do
   Fetch current ASOS observations for all stations in the given state networks.
   Returns `{:ok, [%{station_code, lat, lon, temp_f, dewpoint_f, ...}]}`.
   """
+  @spec fetch_current_asos([String.t()]) :: {:ok, [map()]}
   def fetch_current_asos(state_networks) do
     results =
       state_networks
@@ -175,10 +184,12 @@ defmodule Microwaveprop.Weather.IemClient do
 
   # --- Parsers ---
 
+  @spec parse_iemre_json(map()) :: [map()]
   def parse_iemre_json(json) when is_map(json) do
     Map.get(json, "data", [])
   end
 
+  @spec parse_network_json(map()) :: [map()]
   def parse_network_json(json) when is_map(json) do
     json
     |> Map.get("stations", [])
@@ -192,6 +203,7 @@ defmodule Microwaveprop.Weather.IemClient do
     end)
   end
 
+  @spec parse_asos_csv(String.t()) :: [map()]
   def parse_asos_csv(csv_text) do
     csv_text
     |> String.split("\n")
@@ -201,6 +213,7 @@ defmodule Microwaveprop.Weather.IemClient do
     |> Enum.map(&parse_asos_row/1)
   end
 
+  @spec parse_raob_json(map()) :: [map()]
   def parse_raob_json(json) when is_map(json) do
     json
     |> Map.get("profiles", [])
diff --git a/lib/microwaveprop/weather/iemre_observation.ex b/lib/microwaveprop/weather/iemre_observation.ex
index 8e9737ce..aeed3030 100644
--- a/lib/microwaveprop/weather/iemre_observation.ex
+++ b/lib/microwaveprop/weather/iemre_observation.ex
@@ -16,9 +16,12 @@ defmodule Microwaveprop.Weather.IemreObservation do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(lat lon date)a
   @optional_fields ~w(hourly)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(observation, attrs) do
     observation
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/metar_5min_observation.ex b/lib/microwaveprop/weather/metar_5min_observation.ex
index bc860978..5303ae88 100644
--- a/lib/microwaveprop/weather/metar_5min_observation.ex
+++ b/lib/microwaveprop/weather/metar_5min_observation.ex
@@ -30,9 +30,12 @@ defmodule Microwaveprop.Weather.Metar5minObservation do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(station_id observed_at)a
   @optional_fields ~w(temp_f dewpoint_f relative_humidity wind_speed_kts wind_direction_deg sea_level_pressure_mb altimeter_setting sky_condition precip_1h_in wx_codes)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(observation, attrs) do
     observation
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/ncei_metar_client.ex b/lib/microwaveprop/weather/ncei_metar_client.ex
index f2eb1002..7eb21039 100644
--- a/lib/microwaveprop/weather/ncei_metar_client.ex
+++ b/lib/microwaveprop/weather/ncei_metar_client.ex
@@ -21,6 +21,7 @@ defmodule Microwaveprop.Weather.NceiMetarClient do
 
   Returns `{:ok, [parsed_obs]}` or `{:error, reason}`.
   """
+  @spec fetch(String.t(), pos_integer(), pos_integer()) :: {:ok, [map()]} | {:error, term()}
   def fetch(icao, year, month) do
     month_str = month |> Integer.to_string() |> String.pad_leading(2, "0")
     url = "#{@base_url}/#{year}/#{month_str}/asos-5min-#{icao}-#{year}#{month_str}.dat"
@@ -44,6 +45,7 @@ defmodule Microwaveprop.Weather.NceiMetarClient do
   the key fields without a full METAR parser — this covers the data
   the scorer and backtest need (temp, dewpoint, wind, pressure, sky).
   """
+  @spec parse(String.t()) :: [map()]
   def parse(text) when is_binary(text) do
     text
     |> String.split("\n")
diff --git a/lib/microwaveprop/weather/nexrad_observation.ex b/lib/microwaveprop/weather/nexrad_observation.ex
index 4457c7e6..f59924d2 100644
--- a/lib/microwaveprop/weather/nexrad_observation.ex
+++ b/lib/microwaveprop/weather/nexrad_observation.ex
@@ -19,9 +19,12 @@ defmodule Microwaveprop.Weather.NexradObservation do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(observed_at lat lon)a
   @optional_fields ~w(mean_reflectivity_dbz max_reflectivity_dbz texture_variance pixel_count)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(observation, attrs) do
     observation
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/rtma_client.ex b/lib/microwaveprop/weather/rtma_client.ex
index 47ea65d0..79797e5c 100644
--- a/lib/microwaveprop/weather/rtma_client.ex
+++ b/lib/microwaveprop/weather/rtma_client.ex
@@ -33,6 +33,7 @@ defmodule Microwaveprop.Weather.RtmaClient do
   Fetch RTMA observation for a point at a specific time.
   Returns {:ok, attrs} or {:error, reason}.
   """
+  @spec fetch_observation(float(), float(), DateTime.t()) :: {:ok, map()} | {:error, term()}
   def fetch_observation(lat, lon, timestamp) do
     # RTMA runs every hour with 15-min updates; round to nearest hour
     valid_time = %{DateTime.truncate(timestamp, :second) | minute: 0, second: 0}
@@ -63,6 +64,7 @@ defmodule Microwaveprop.Weather.RtmaClient do
   end
 
   @doc "Build S3 URL for an RTMA analysis file."
+  @spec rtma_url(DateTime.t()) :: String.t()
   def rtma_url(valid_time) do
     date_str = Calendar.strftime(valid_time, "%Y%m%d")
     hour_str = valid_time.hour |> Integer.to_string() |> String.pad_leading(2, "0")
diff --git a/lib/microwaveprop/weather/rtma_observation.ex b/lib/microwaveprop/weather/rtma_observation.ex
index 53b6bee4..94e458e0 100644
--- a/lib/microwaveprop/weather/rtma_observation.ex
+++ b/lib/microwaveprop/weather/rtma_observation.ex
@@ -22,9 +22,12 @@ defmodule Microwaveprop.Weather.RtmaObservation do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(valid_time lat lon)a
   @optional_fields ~w(temp_c dewpoint_c pressure_mb wind_u_ms wind_v_ms visibility_m precip_mm)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(observation, attrs) do
     observation
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/solar_client.ex b/lib/microwaveprop/weather/solar_client.ex
index 953057d9..d0500f9f 100644
--- a/lib/microwaveprop/weather/solar_client.ex
+++ b/lib/microwaveprop/weather/solar_client.ex
@@ -3,8 +3,10 @@ defmodule Microwaveprop.Weather.SolarClient do
 
   @gfz_url "https://kp.gfz.de/app/files/Kp_ap_Ap_SN_F107_since_1932.txt"
 
+  @spec data_url() :: String.t()
   def data_url, do: @gfz_url
 
+  @spec fetch_solar_indices() :: {:ok, [map()]} | {:error, term()}
   def fetch_solar_indices do
     req_options = Application.get_env(:microwaveprop, :solar_req_options, [])
 
@@ -20,10 +22,12 @@ defmodule Microwaveprop.Weather.SolarClient do
     end
   end
 
+  @spec filter_since([map()], Date.t()) :: [map()]
   def filter_since(records, since_date) do
     Enum.filter(records, fn r -> Date.compare(r.date, since_date) != :lt end)
   end
 
+  @spec parse_gfz_file(String.t()) :: [map()]
   def parse_gfz_file(text) do
     text
     |> String.split("\n")
@@ -39,6 +43,7 @@ defmodule Microwaveprop.Weather.SolarClient do
     end)
   end
 
+  @spec parse_gfz_row(String.t()) :: {:ok, map()} | :error
   def parse_gfz_row(line) do
     fields = String.split(line)
 
diff --git a/lib/microwaveprop/weather/solar_index.ex b/lib/microwaveprop/weather/solar_index.ex
index c19cb276..6570c51f 100644
--- a/lib/microwaveprop/weather/solar_index.ex
+++ b/lib/microwaveprop/weather/solar_index.ex
@@ -17,9 +17,12 @@ defmodule Microwaveprop.Weather.SolarIndex do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(date)a
   @optional_fields ~w(sfi sfi_adjusted sunspot_number ap_index kp_values)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(solar_index, attrs) do
     solar_index
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/sounding.ex b/lib/microwaveprop/weather/sounding.ex
index 82899c58..db00d3d9 100644
--- a/lib/microwaveprop/weather/sounding.ex
+++ b/lib/microwaveprop/weather/sounding.ex
@@ -27,9 +27,12 @@ defmodule Microwaveprop.Weather.Sounding do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(station_id observed_at profile level_count)a
   @optional_fields ~w(surface_pressure_mb surface_temp_c surface_dewpoint_c surface_refractivity min_refractivity_gradient boundary_layer_depth_m precipitable_water_mm k_index lifted_index ducting_detected duct_characteristics)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(sounding, attrs) do
     sounding
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/sounding_params.ex b/lib/microwaveprop/weather/sounding_params.ex
index 7fd1e01b..f6242427 100644
--- a/lib/microwaveprop/weather/sounding_params.ex
+++ b/lib/microwaveprop/weather/sounding_params.ex
@@ -2,11 +2,13 @@ defmodule Microwaveprop.Weather.SoundingParams do
   @moduledoc false
 
   @doc "Buck equation for saturation vapor pressure (hPa) given temperature in °C."
+  @spec sat_vap_pres(float()) :: float()
   def sat_vap_pres(t_c) do
     6.1121 * :math.exp((18.678 - t_c / 234.5) * (t_c / (257.14 + t_c)))
   end
 
   @doc "Mixing ratio (g/kg) from dewpoint (°C) and pressure (hPa)."
+  @spec mixing_ratio(float(), float()) :: float()
   def mixing_ratio(t_c, p_mb) do
     e = sat_vap_pres(t_c)
     622.0 * e / (p_mb - e)
@@ -18,6 +20,7 @@ defmodule Microwaveprop.Weather.SoundingParams do
   Profile is a list of maps with keys: "pres", "hght", "tmpc", "dwpc", "drct", "sknt".
   Returns nil if fewer than 3 valid levels.
   """
+  @spec derive([map()]) :: map() | nil
   def derive(profile) when is_list(profile) do
     sorted =
       profile
diff --git a/lib/microwaveprop/weather/station.ex b/lib/microwaveprop/weather/station.ex
index 9491bdb4..efb2664a 100644
--- a/lib/microwaveprop/weather/station.ex
+++ b/lib/microwaveprop/weather/station.ex
@@ -20,9 +20,12 @@ defmodule Microwaveprop.Weather.Station do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(station_code station_type name lat lon)a
   @optional_fields ~w(wmo_number elevation_m state)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(station, attrs) do
     station
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/surface_observation.ex b/lib/microwaveprop/weather/surface_observation.ex
index ce5e3025..50577aa1 100644
--- a/lib/microwaveprop/weather/surface_observation.ex
+++ b/lib/microwaveprop/weather/surface_observation.ex
@@ -24,9 +24,12 @@ defmodule Microwaveprop.Weather.SurfaceObservation do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @required_fields ~w(station_id observed_at)a
   @optional_fields ~w(temp_f dewpoint_f relative_humidity wind_speed_kts wind_direction_deg sea_level_pressure_mb altimeter_setting sky_condition precip_1h_in wx_codes)a
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(observation, attrs) do
     observation
     |> cast(attrs, @required_fields ++ @optional_fields)
diff --git a/lib/microwaveprop/weather/weather_layers.ex b/lib/microwaveprop/weather/weather_layers.ex
index 6325114c..d1a676a5 100644
--- a/lib/microwaveprop/weather/weather_layers.ex
+++ b/lib/microwaveprop/weather/weather_layers.ex
@@ -13,6 +13,7 @@ defmodule Microwaveprop.Weather.WeatherLayers do
   `:temp_850mb`, `:dewpoint_850mb`, `:lapse_rate`, `:inversion_strength`,
   `:inversion_base_m`, `:duct_base_m`, `:duct_strength`.
   """
+  @spec derive(map()) :: map()
   def derive(row) do
     sorted = sort_profile(row.profile)