diff --git a/tests/test_syntax_validation.py b/tests/test_syntax_validation.py
new file mode 100644
index 000000000..e33fd8707
--- /dev/null
+++ b/tests/test_syntax_validation.py
@@ -0,0 +1,82 @@
+"""Tests for Python syntax validation in execute_code."""
+
+import json
+import sys
+import os
+from pathlib import Path
+
+import pytest
+
+# Import the validation function directly
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+from tools.code_execution_tool import _validate_python_syntax
+
+
+class TestValidatePythonSyntax:
+    """Test _validate_python_syntax catches errors before subprocess spawn."""
+
+    def test_valid_code_returns_none(self):
+        assert _validate_python_syntax("print('hello')") is None
+
+    def test_valid_multiline_returns_none(self):
+        code = """
+import os
+def foo():
+    return 42
+result = foo()
+"""
+        assert _validate_python_syntax(code) is None
+
+    def test_syntax_error_detected(self):
+        result = _validate_python_syntax("def foo(
+")
+        assert result is not None
+        data = json.loads(result)
+        assert data["syntax_error"] is True
+        assert "line" in data
+        assert "message" in data
+
+    def test_missing_colon(self):
+        result = _validate_python_syntax("def foo()
+    pass")
+        data = json.loads(result)
+        assert data["syntax_error"] is True
+        assert data["line"] == 1
+
+    def test_unmatched_paren(self):
+        result = _validate_python_syntax("print('hello'")
+        data = json.loads(result)
+        assert data["syntax_error"] is True
+
+    def test_indentation_error(self):
+        result = _validate_python_syntax("def foo():
+pass")
+        data = json.loads(result)
+        assert data["syntax_error"] is True
+        assert data["line"] == 2
+
+    def test_invalid_character(self):
+        result = _validate_python_syntax("x = 5 √ 2")
+        data = json.loads(result)
+        assert data["syntax_error"] is True
+
+    def test_error_format_has_required_fields(self):
+        result = _validate_python_syntax("def(
+")
+        data = json.loads(result)
+        assert "error" in data
+        assert "syntax_error" in data
+        assert "line" in data
+        assert "offset" in data
+        assert "message" in data
+
+    def test_empty_string_returns_none(self):
+        # Empty code is caught by the guard before validation
+        # But if called directly, ast.parse("") is valid
+        assert _validate_python_syntax("") is None
+
+    def test_comment_only_returns_none(self):
+        assert _validate_python_syntax("# just a comment") is None
+
+    def test_complex_valid_code(self):
+        code = 
\ No newline at end of file