diff --git a/assets/css/app.css b/assets/css/app.css
index b34f75c3..dcdd49c3 100644
--- a/assets/css/app.css
+++ b/assets/css/app.css
@@ -1,9 +1,9 @@
 /* Leaflet map CSS (vendored) */
 @import "../vendor/leaflet/leaflet.css";
 
-/* Inter — primary UI font. Design spec calls for weights 400/500/600/700.
-   JetBrains Mono kept as escape hatch for code blocks. */
-@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500;600&display=swap');
+/* Cascadia Code as the single project font. Google Fonts doesn't
+   ship it — fonts.cdnfonts.com mirrors Microsoft's release. */
+@import url('https://fonts.cdnfonts.com/css/cascadia-code');
 
 /* See the Tailwind configuration guide for advanced usage
    https://tailwindcss.com/docs/configuration */
@@ -15,6 +15,15 @@
 @source "../../deps/live_table/lib";
 @source "../../deps/sutra_ui/lib";
 
+/* Map both Tailwind font families onto Cascadia Code so any element
+   hard-coded to font-sans or font-mono picks up the project font.
+   Keep the system fallbacks so the page is still readable while the
+   webfont network request is in flight. */
+@theme {
+  --font-sans: "Cascadia Code", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  --font-mono: "Cascadia Code", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+}
+
 /* live_table / sutra_ui compat: maps shadcn tokens live_table uses to
    daisyUI base colors and provides component CSS for the SutraUI
    primitives wrapped by live_table (select, input-group, dropdown,
@@ -166,13 +175,13 @@
   --band-6mm:    #0891B2;
 }
 
-/* Inter as the default UI font. JetBrains Mono reserved for code blocks.
-   Callsigns and grid squares are intentionally sans + uppercase (not mono)
-   to match product convention. */
+/* Cascadia Code everywhere — UI, body copy, and code. The font is
+   monospace by design; we tighten letter-spacing slightly so prose
+   blocks don't read excessively wide. */
 html, body {
   font-family:
-    "Inter", ui-sans-serif, system-ui, -apple-system,
-    "Segoe UI", Roboto, sans-serif;
+    "Cascadia Code", ui-monospace, SFMono-Regular, "Menlo", "Consolas",
+    monospace;
   -webkit-font-smoothing: antialiased;
   text-rendering: optimizeLegibility;
   font-variant-numeric: tabular-nums;
@@ -247,7 +256,7 @@ select.select {
 }
 
 .markdown-content code {
-  font-family: ui-monospace, monospace;
+  font-family: "Cascadia Code", ui-monospace, monospace;
   font-size: 0.875em;
   background: var(--color-base-300);
   padding: 0.15em 0.35em;
diff --git a/assets/js/path_forecast_hook.ts b/assets/js/path_forecast_hook.ts
index 2272225d..054b622a 100644
--- a/assets/js/path_forecast_hook.ts
+++ b/assets/js/path_forecast_hook.ts
@@ -55,7 +55,7 @@ function buildHTML(detail: PathForecastDetail): string {
     const pct = Math.round(meta.weight * 100)
     rows += `<tr>
       <td style="padding:1px 6px 1px 0;white-space:nowrap;font-size:11px;">${meta.label}</td>
-      <td style="padding:1px 4px;font-family:monospace;font-size:11px;letter-spacing:-0.5px;">${factorBar(value)}</td>
+      <td style="padding:1px 4px;font-family:'Cascadia Code',monospace;font-size:11px;letter-spacing:-0.5px;">${factorBar(value)}</td>
       <td style="padding:1px 4px;text-align:right;font-size:11px;font-weight:600;">${value}</td>
       <td style="padding:1px 4px;font-size:10px;opacity:0.5;">(${pct}%)</td>
     </tr>`
diff --git a/assets/js/propagation_map_hook.ts b/assets/js/propagation_map_hook.ts
index c4dc5005..34a8b114 100644
--- a/assets/js/propagation_map_hook.ts
+++ b/assets/js/propagation_map_hook.ts
@@ -590,7 +590,7 @@ function buildPopupHTML(detail: PointDetail, viewshedLoading: boolean): string {
     const pct = Math.round(meta.weight * 100)
     rows += `<tr>
       <td style="padding:1px 6px 1px 0;white-space:nowrap;font-size:11px;">${meta.label}</td>
-      <td style="padding:1px 4px;font-family:monospace;font-size:11px;letter-spacing:-0.5px;">${factorBar(value)}</td>
+      <td style="padding:1px 4px;font-family:'Cascadia Code',monospace;font-size:11px;letter-spacing:-0.5px;">${factorBar(value)}</td>
       <td style="padding:1px 4px;text-align:right;font-size:11px;font-weight:600;">${value}</td>
       <td style="padding:1px 4px;font-size:10px;opacity:0.5;">(${pct}%)</td>
     </tr>`