diff --git a/test/snmpkit/snmp_lib/mib/snmp_tokenizer_test.exs b/test/snmpkit/snmp_lib/mib/snmp_tokenizer_test.exs
new file mode 100644
index 00000000..0364cc0d
--- /dev/null
+++ b/test/snmpkit/snmp_lib/mib/snmp_tokenizer_test.exs
@@ -0,0 +1,522 @@
+defmodule SnmpKit.SnmpLib.MIB.SnmpTokenizerTest do
+  use ExUnit.Case, async: true
+
+  alias SnmpKit.SnmpLib.MIB.SnmpTokenizer
+
+  describe "tokenize/2" do
+    test "tokenizes empty input" do
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(~c"", &SnmpTokenizer.null_get_line/0)
+      assert [{:"$end", 1}] = tokens
+    end
+
+    test "tokenizes simple MIB header" do
+      input = ~c"TEST-MIB DEFINITIONS ::= BEGIN END"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      # TEST-MIB is tokenized as :variable (uppercase identifier)
+      assert :variable in token_types
+      assert :DEFINITIONS in token_types
+      assert :BEGIN in token_types
+      assert :END in token_types
+    end
+
+    test "tokenizes reserved words" do
+      reserved_words = [
+        "DEFINITIONS",
+        "BEGIN",
+        "END",
+        "IMPORTS",
+        "FROM",
+        "OBJECT-TYPE",
+        "SYNTAX",
+        "MAX-ACCESS",
+        "STATUS",
+        "DESCRIPTION"
+      ]
+
+      for word <- reserved_words do
+        input = String.to_charlist(word)
+        assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+        # First token should be the reserved word
+        assert length(tokens) >= 1
+      end
+    end
+
+    test "tokenizes identifiers" do
+      input = ~c"testObject myIdentifier test123"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      atoms = tokens |> Enum.filter(&match?({:atom, _, _}, &1))
+      assert length(atoms) == 3
+    end
+
+    test "tokenizes numbers" do
+      input = ~c"0 123 456789"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      numbers = tokens |> Enum.filter(&match?({:integer, _, _}, &1))
+      assert length(numbers) == 3
+    end
+
+    test "tokenizes negative numbers" do
+      input = ~c"-1 -123"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Might be tokenized as minus sign + integer, depends on implementation
+      assert length(tokens) >= 2
+    end
+
+    test "tokenizes strings with quotes" do
+      input = ~c"\"test string\" \"another\""
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Strings might be tokenized as :string or just handled as tokens
+      # Just verify tokenization succeeds
+      assert length(tokens) >= 1
+    end
+
+    test "tokenizes special characters" do
+      input = ~c"::= { } ( ) , ; ."
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Should have various special character tokens
+      assert length(tokens) > 5
+    end
+
+    test "tokenizes OID notation" do
+      input = ~c"{ test 1 2 3 }"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Should have braces, identifier, and numbers
+      assert length(tokens) >= 6
+    end
+
+    test "tokenizes complete OBJECT-TYPE definition" do
+      input = ~c"""
+      testObject OBJECT-TYPE
+        SYNTAX Integer32
+        MAX-ACCESS read-only
+        STATUS current
+        DESCRIPTION "Test object"
+        ::= { test 1 }
+      """
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :"OBJECT-TYPE" in token_types
+      assert :SYNTAX in token_types
+      assert :"MAX-ACCESS" in token_types
+      assert :STATUS in token_types
+      assert :DESCRIPTION in token_types
+    end
+
+    test "tokenizes access modifiers" do
+      access_values = ["read-only", "read-write", "not-accessible", "read-create"]
+
+      for access <- access_values do
+        input = String.to_charlist(access)
+        assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+        assert length(tokens) >= 1
+      end
+    end
+
+    test "tokenizes SMI types" do
+      types = ["INTEGER", "OCTET STRING", "Counter32", "Gauge32", "TimeTicks", "IpAddress"]
+
+      for type <- types do
+        input = String.to_charlist(type)
+        assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+        assert length(tokens) >= 1
+      end
+    end
+
+    test "tokenizes hyphenated keywords" do
+      keywords = [
+        "OBJECT-TYPE",
+        "MAX-ACCESS",
+        "MODULE-IDENTITY",
+        "OBJECT-IDENTITY",
+        "TEXTUAL-CONVENTION"
+      ]
+
+      for keyword <- keywords do
+        input = String.to_charlist(keyword)
+        assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+        # Should tokenize as single keyword token
+        non_end_tokens = Enum.reject(tokens, &match?({:"$end", _}, &1))
+        assert length(non_end_tokens) == 1
+      end
+    end
+
+    test "handles whitespace correctly" do
+      input = ~c"  test   123   \n  OBJECT-TYPE  "
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Whitespace should be ignored, only meaningful tokens returned
+      non_end_tokens = Enum.reject(tokens, &match?({:"$end", _}, &1))
+      assert length(non_end_tokens) == 3
+    end
+
+    test "handles comments" do
+      input = ~c"test -- this is a comment\nOBJECT-TYPE"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Comments should be ignored
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :atom in token_types
+      assert :"OBJECT-TYPE" in token_types
+    end
+
+    test "handles multiline input" do
+      input = ~c"""
+      TEST-MIB
+      DEFINITIONS
+      ::=
+      BEGIN
+      END
+      """
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      # TEST-MIB is tokenized as :variable (uppercase identifier)
+      assert :variable in token_types
+      assert :DEFINITIONS in token_types
+      assert :BEGIN in token_types
+      assert :END in token_types
+    end
+
+    test "tokenizes with line numbers" do
+      input = ~c"test\nDEFINITIONS\nBEGIN"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      # Tokens should have different line numbers
+      lines = Enum.map(tokens, fn
+        {_type, line} -> line
+        {_type, _value, line} -> line
+      end)
+
+      assert Enum.uniq(lines) |> length() > 1
+    end
+
+    test "preserves token order" do
+      input = ~c"first second third"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      atoms = tokens |> Enum.filter(&match?({:atom, _, _}, &1))
+
+      # Should be in order
+      assert length(atoms) == 3
+    end
+
+    test "handles complex MIB structure" do
+      input = ~c"""
+      TEST-MIB DEFINITIONS ::= BEGIN
+      IMPORTS
+        MODULE-IDENTITY FROM SNMPv2-SMI;
+
+      testMIB MODULE-IDENTITY
+        LAST-UPDATED "202501010000Z"
+        ORGANIZATION "Test Org"
+        ::= { test 1 }
+      END
+      """
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :DEFINITIONS in token_types
+      assert :BEGIN in token_types
+      assert :IMPORTS in token_types
+      assert :"MODULE-IDENTITY" in token_types
+      assert :FROM in token_types
+      assert :END in token_types
+    end
+
+    test "tokenizes SIZE constraint" do
+      input = ~c"SIZE (0..255)"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :SIZE in token_types
+    end
+
+    test "tokenizes SEQUENCE OF" do
+      input = ~c"SEQUENCE OF TestEntry"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :SEQUENCE in token_types
+      assert :OF in token_types
+    end
+  end
+
+  describe "format_error/1" do
+    test "formats illegal character error" do
+      error = {:illegal, ?@}
+      formatted = SnmpTokenizer.format_error(error)
+
+      assert is_list(formatted)
+      formatted_str = List.to_string(formatted)
+      assert formatted_str =~ "illegal character"
+    end
+
+    test "formats unterminated string error" do
+      error = {:unterminated_string, 42}
+      formatted = SnmpTokenizer.format_error(error)
+
+      assert is_list(formatted)
+      formatted_str = List.to_string(formatted)
+      assert formatted_str =~ "unterminated string"
+      assert formatted_str =~ "42"
+    end
+
+    test "formats unterminated quote error" do
+      error = {:unterminated_quote, 10}
+      formatted = SnmpTokenizer.format_error(error)
+
+      assert is_list(formatted)
+      formatted_str = List.to_string(formatted)
+      assert formatted_str =~ "unterminated quote"
+      assert formatted_str =~ "10"
+    end
+
+    test "formats unknown error" do
+      error = {:unknown_error, "details"}
+      formatted = SnmpTokenizer.format_error(error)
+
+      assert is_list(formatted)
+    end
+
+    test "formats atom error" do
+      error = :some_error
+      formatted = SnmpTokenizer.format_error(error)
+
+      assert is_list(formatted)
+    end
+  end
+
+  describe "null_get_line/0" do
+    test "returns eof" do
+      assert SnmpTokenizer.null_get_line() == :eof
+    end
+  end
+
+  describe "test/0" do
+    test "runs test function without crashing" do
+      # The test/0 function tokenizes a test string and prints output
+      # We just verify it doesn't crash
+      assert SnmpTokenizer.test() in [:ok, :error]
+    end
+  end
+
+  describe "edge cases" do
+    test "handles very long identifiers" do
+      # Use a more reasonable length to avoid atom table limits (255 bytes max for atoms)
+      long_id = String.duplicate("a", 200) |> String.to_charlist()
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(long_id, &SnmpTokenizer.null_get_line/0)
+      assert length(tokens) >= 1
+    end
+
+    test "handles many tokens" do
+      # Create input with many identifiers
+      identifiers = Enum.map(1..100, fn i -> "id#{i}" end) |> Enum.join(" ")
+      input = String.to_charlist(identifiers)
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+      atoms = tokens |> Enum.filter(&match?({:atom, _, _}, &1))
+      assert length(atoms) == 100
+    end
+
+    test "handles deeply nested braces" do
+      input = ~c"{ { { test } } }"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+      assert length(tokens) > 6
+    end
+
+    test "handles mixed case keywords" do
+      # Reserved words should be case-sensitive
+      input = ~c"begin BEGIN"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      # Only "BEGIN" should be recognized as keyword
+      begin_count = Enum.count(token_types, &(&1 == :BEGIN))
+      assert begin_count == 1
+
+      # "begin" should be an atom (lowercase identifier)
+      atom_count = Enum.count(tokens, &match?({:atom, _, _}, &1))
+      assert atom_count >= 1
+    end
+
+    test "handles unicode characters in strings" do
+      # Basic ASCII string should work
+      input = ~c"\"test\""
+
+      assert {:ok, _tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+    end
+
+    test "handles empty strings" do
+      input = ~c"\"\""
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+      assert length(tokens) >= 1
+    end
+
+    test "handles consecutive operators" do
+      input = ~c"::=::="
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+      # Should tokenize as two ::= operators or similar
+      assert length(tokens) >= 2
+    end
+
+    test "handles tabs and mixed whitespace" do
+      input = ~c"test\t\tOBJECT-TYPE\n\n  BEGIN"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      assert :atom in token_types
+      assert :"OBJECT-TYPE" in token_types
+      assert :BEGIN in token_types
+    end
+
+    test "handles numbers with leading zeros" do
+      input = ~c"001 0123"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      integers = tokens |> Enum.filter(&match?({:integer, _, _}, &1))
+      assert length(integers) == 2
+    end
+
+    test "handles very large numbers" do
+      input = ~c"999999999999"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      integers = tokens |> Enum.filter(&match?({:integer, _, _}, &1))
+      assert length(integers) == 1
+    end
+  end
+
+  describe "reserved word coverage" do
+    test "tokenizes all common reserved words" do
+      # Test a sampling of reserved words to ensure coverage
+      words = [
+        "DEFINITIONS",
+        "BEGIN",
+        "END",
+        "IMPORTS",
+        "FROM",
+        "EXPORTS",
+        "OBJECT",
+        "IDENTIFIER",
+        "OBJECT-TYPE",
+        "SYNTAX",
+        "ACCESS",
+        "MAX-ACCESS",
+        "STATUS",
+        "DESCRIPTION",
+        "REFERENCE",
+        "INDEX",
+        "SEQUENCE",
+        "OF",
+        "SIZE",
+        "INTEGER",
+        "OCTET",
+        "STRING",
+        "Counter32",
+        "Gauge32",
+        "MODULE-IDENTITY",
+        "TEXTUAL-CONVENTION",
+        "OBJECT-GROUP",
+        "NOTIFICATION-TYPE"
+      ]
+
+      for word <- words do
+        input = String.to_charlist(word)
+        assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+        # Should successfully tokenize without error
+        assert length(tokens) >= 1
+      end
+    end
+
+    test "distinguishes reserved words from similar identifiers" do
+      # "OBJECT" is reserved, "object" is lowercase atom
+      input = ~c"OBJECT object"
+
+      assert {:ok, tokens} = SnmpTokenizer.tokenize(input, &SnmpTokenizer.null_get_line/0)
+
+      token_types = Enum.map(tokens, fn
+        {type, _line} -> type
+        {type, _value, _line} -> type
+      end)
+
+      # OBJECT should be keyword
+      assert :OBJECT in token_types
+
+      # "object" should be an atom (lowercase identifier)
+      atoms = tokens |> Enum.filter(&match?({:atom, _, _}, &1))
+      assert length(atoms) >= 1
+    end
+  end
+end