diff --git a/scripts/validate_architecture.py b/scripts/validate_architecture.py
index e26db0a3..e3f0f3cd 100755
--- a/scripts/validate_architecture.py
+++ b/scripts/validate_architecture.py
@@ -1102,6 +1102,56 @@ class ArchitectureValidator:
                         suggestion=f"Use '{{% block {invalid_blocks[block_name]} %}}' instead",
                     )
 
+    def _check_alpine_template_vars(
+        self, file_path: Path, content: str, lines: list[str], js_content: str
+    ):
+        """TPL-009: Check that Alpine variables used in templates are defined in JS"""
+        if "noqa: tpl-009" in content.lower():
+            return
+
+        import re
+
+        # Common Alpine variable patterns that MUST be defined in the component
+        # These are variables that are directly referenced in templates
+        required_vars = set()
+
+        # Check for error_state macro usage (requires 'error' var)
+        if "error_state(" in content and "error_var=" not in content:
+            required_vars.add("error")
+
+        # Check for action_dropdown macro with custom vars
+        dropdown_pattern = re.compile(
+            r"action_dropdown\([^)]*open_var=['\"](\w+)['\"]"
+        )
+        for match in dropdown_pattern.finditer(content):
+            required_vars.add(match.group(1))
+
+        dropdown_pattern2 = re.compile(
+            r"action_dropdown\([^)]*loading_var=['\"](\w+)['\"]"
+        )
+        for match in dropdown_pattern2.finditer(content):
+            required_vars.add(match.group(1))
+
+        # Check if variables are defined in JS
+        for var in required_vars:
+            # Check if variable is defined in JS (look for "varname:" pattern)
+            var_pattern = re.compile(rf"\b{var}\s*:")
+            if not var_pattern.search(js_content):
+                # Find the line where it's used in template
+                for i, line in enumerate(lines, 1):
+                    if var in line and ("error_state" in line or "action_dropdown" in line):
+                        self._add_violation(
+                            rule_id="TPL-009",
+                            rule_name="Alpine variables must be defined in JS component",
+                            severity=Severity.ERROR,
+                            file_path=file_path,
+                            line_number=i,
+                            message=f"Template uses Alpine variable '{var}' but it's not defined in the JS component",
+                            context=line.strip()[:80],
+                            suggestion=f"Add '{var}: null,' or '{var}: false,' to the Alpine component's return object",
+                        )
+                        break
+
     def _check_pagination_macro_usage(
         self, file_path: Path, content: str, lines: list[str]
     ):
@@ -2717,6 +2767,16 @@ class ArchitectureValidator:
             if not is_base_or_partial:
                 self._check_valid_block_names(file_path, content, lines)
 
+            # TPL-009: Check Alpine variables are defined in JS
+            if not is_base_or_partial and not is_macro and not is_components_page:
+                # Try to find corresponding JS file
+                # Template: app/templates/admin/messages.html -> JS: static/admin/js/messages.js
+                template_name = file_path.stem  # e.g., "messages"
+                js_file = target_path / f"static/admin/js/{template_name}.js"
+                if js_file.exists():
+                    js_content = js_file.read_text()
+                    self._check_alpine_template_vars(file_path, content, lines, js_content)
+
             # Skip base/partials for TPL-001 check
             if is_base_or_partial:
                 continue