fix: accept both string and dict for body/params in n8n_api_call

Handle the case where MCP clients may pass JSON as either a string or
dict object. Adds _normalize_json_param helper to handle both formats
gracefully, preventing Pydantic validation errors.

server.py

@@ -338,12 +338,34 @@ async def trigger_webhook(
 # =============================================================================
 
 
+def _normalize_json_param(value: str | dict[str, Any] | None) -> dict[str, Any]:
+    """Normalize a parameter that can be either a JSON string or a dict.
+
+    This handles the case where MCP clients may pass either:
+    - A JSON string: '{"key": "value"}'
+    - A dict object: {"key": "value"}
+    """
+    if value is None:
+        return {}
+    if isinstance(value, dict):
+        return value
+    if isinstance(value, str):
+        if not value or value == "{}":
+            return {}
+        try:
+            parsed = json.loads(value)
+            return parsed if isinstance(parsed, dict) else {}
+        except json.JSONDecodeError:
+            return {}
+    return {}
+
+
 @mcp.tool()
 async def n8n_api_call(
     endpoint: str,
     method: str = "GET",
-    params: str = "{}",
+    params: str | dict[str, Any] | None = None,
-    body: str = "{}",
+    body: str | dict[str, Any] | None = None,
 ) -> str:
     """Execute a raw API call to n8n.
 
@@ -353,8 +375,8 @@ async def n8n_api_call(
     Args:
         endpoint: API endpoint path (e.g., '/workflows', '/credentials')
         method: HTTP method (GET, POST, PUT, PATCH, DELETE)
-        params: JSON string of query parameters (optional)
+        params: Query parameters as JSON string or dict (optional)
-        body: JSON string of request body for POST/PUT/PATCH (optional)
+        body: Request body as JSON string or dict for POST/PUT/PATCH (optional)
 
     Examples:
         - Create workflow: n8n_api_call('/workflows', 'POST', body='{"name": "My Workflow", "nodes": [...], "connections": {...}}')
@@ -362,11 +384,8 @@ async def n8n_api_call(
         - List credentials: n8n_api_call('/credentials')
         - Create tag: n8n_api_call('/tags', 'POST', body='{"name": "production"}')
     """
-    try:
+    params_dict = _normalize_json_param(params)
-        params_dict = json.loads(params) if params else {}
+    body_dict = _normalize_json_param(body)
-        body_dict = json.loads(body) if body else {}
-    except json.JSONDecodeError as e:
-        return json.dumps({"error": True, "message": f"Invalid JSON: {e}"})
 
     result = await client.request(
         method=method,