fix: auto-inject webhookId on webhook nodes during create/update (#643) (#657)

n8n 2.10+ requires webhookId (UUID) on webhook-type nodes for proper
webhook URL registration. Without it, webhooks silently fail with 404.
The n8n UI always generates webhookId but programmatic creation via
n8n-mcp did not.

Add ensureWebhookIds() helper that injects crypto.randomUUID() on
webhook, webhookTrigger, formTrigger, and chatTrigger nodes when
webhookId is missing. Called from both cleanWorkflowForCreate() and
cleanWorkflowForUpdate(). Existing webhookId values are preserved.

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,34 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.40.5] - 2026-03-22
+
+### Fixed
+
+- **Webhook workflows created via MCP get 404 errors** (Issue #643): Auto-inject `webhookId` (UUID) on webhook-type nodes (`webhook`, `webhookTrigger`, `formTrigger`, `chatTrigger`) during `cleanWorkflowForCreate()` and `cleanWorkflowForUpdate()`. n8n 2.10+ requires this field for proper webhook URL registration; without it, webhooks silently fail with 404. Existing `webhookId` values are preserved.
+
+Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en
+
+## [2.40.4] - 2026-03-22
+
+### Fixed
+
+- **Incorrect data tables availability info**: Removed "enterprise/cloud only" restriction from tool description and documentation — data tables are available on all n8n plans including self-hosted
+- **Redundant pitfalls removed**: Removed "Requires N8N_API_URL and N8N_API_KEY" and "enterprise or cloud plans" pitfalls — the first is implicit for all n8n management tools, the second was incorrect
+
+Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en
+
+## [2.40.3] - 2026-03-22
+
+### Fixed
+
+- **Notification 400 disconnect storms (#654)**: `handleRequest()` now returns 202 Accepted for JSON-RPC notifications with stale/expired session IDs instead of 400. Per JSON-RPC 2.0 spec, notifications don't expect responses — returning 400 caused Claude's proxy to trigger reconnection storms (930 errors/day, 216 users affected)
+- **TOCTOU race in session lookup**: Added null guard after transport assignment to handle sessions removed between the existence check and use
+- **`updateTable` silently ignoring `columns` parameter**: Now returns a warning message when `columns` is passed to `updateTable`, clarifying that table schema is immutable after creation via the public API
+- **Tool schema descriptions clarified**: `name` and `columns` parameter descriptions now explicitly document that `updateTable` is rename-only and columns are for `createTable` only
+
+Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en
+
 ## [2.40.2] - 2026-03-22
 
 ### Fixed

dist/services/n8n-validation.d.ts.map

@@ -1 +1 @@
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dist/services/n8n-validation.js

@@ -1,4 +1,7 @@
 "use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
 Object.defineProperty(exports, "__esModule", { value: true });
 exports.defaultWorkflowSettings = exports.workflowSettingsSchema = exports.workflowConnectionSchema = exports.workflowNodeSchema = void 0;
 exports.validateWorkflowNode = validateWorkflowNode;
@@ -13,6 +16,7 @@ exports.validateOperatorStructure = validateOperatorStructure;
 exports.getWebhookUrl = getWebhookUrl;
 exports.getWorkflowStructureExample = getWorkflowStructureExample;
 exports.getWorkflowFixSuggestions = getWorkflowFixSuggestions;
+const crypto_1 = __importDefault(require("crypto"));
 const zod_1 = require("zod");
 const node_type_utils_1 = require("../utils/node-type-utils");
 const node_classification_1 = require("../utils/node-classification");
@@ -76,11 +80,27 @@ function validateWorkflowConnections(connections) {
 function validateWorkflowSettings(settings) {
     return exports.workflowSettingsSchema.parse(settings);
 }
+const WEBHOOK_NODE_TYPES = new Set([
+    'n8n-nodes-base.webhook',
+    'n8n-nodes-base.webhookTrigger',
+    'n8n-nodes-base.formTrigger',
+    '@n8n/n8n-nodes-langchain.chatTrigger',
+]);
+function ensureWebhookIds(nodes) {
+    if (!nodes)
+        return;
+    for (const node of nodes) {
+        if (WEBHOOK_NODE_TYPES.has(node.type) && !node.webhookId) {
+            node.webhookId = crypto_1.default.randomUUID();
+        }
+    }
+}
 function cleanWorkflowForCreate(workflow) {
     const { id, createdAt, updatedAt, versionId, meta, active, tags, ...cleanedWorkflow } = workflow;
     if (!cleanedWorkflow.settings || Object.keys(cleanedWorkflow.settings).length === 0) {
         cleanedWorkflow.settings = exports.defaultWorkflowSettings;
     }
+    ensureWebhookIds(cleanedWorkflow.nodes);
     return cleanedWorkflow;
 }
 function cleanWorkflowForUpdate(workflow) {
@@ -116,6 +136,7 @@ function cleanWorkflowForUpdate(workflow) {
     else {
         cleanedWorkflow.settings = { executionOrder: 'v1' };
     }
+    ensureWebhookIds(cleanedWorkflow.nodes);
     return cleanedWorkflow;
 }
 function validateWorkflowStructure(workflow) {

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "n8n-mcp",
-  "version": "2.37.3",
+  "version": "2.40.5",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "n8n-mcp",
-      "version": "2.37.3",
+      "version": "2.40.5",
       "license": "MIT",
       "dependencies": {
         "@modelcontextprotocol/sdk": "^1.27.1",

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.40.2",
+  "version": "2.40.5",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/http-server-single-session.ts

@@ -254,6 +254,22 @@ export class SingleSessionHTTPServer {
     return Boolean(sessionId && sessionId.length > 0);
   }
 
+  /**
+   * Checks if a request body is a JSON-RPC notification (or batch of only notifications).
+   * Per JSON-RPC 2.0 §4.1, a notification is a request without an "id" member.
+   * Note: `!('id' in msg)` is strict — messages with `id: null` are treated as
+   * requests, not notifications. This is spec-compliant.
+   */
+  private isJsonRpcNotification(body: unknown): boolean {
+    if (!body || typeof body !== 'object') return false;
+    const isSingleNotification = (msg: any): boolean =>
+      msg && typeof msg.method === 'string' && !('id' in msg);
+    if (Array.isArray(body)) {
+      return body.length > 0 && body.every(isSingleNotification);
+    }
+    return isSingleNotification(body);
+  }
+  
   /**
    * Sanitize error information for client responses
    */
@@ -614,6 +630,22 @@ export class SingleSessionHTTPServer {
           logger.info('handleRequest: Reusing existing transport for session', { sessionId });
           transport = this.transports[sessionId];
 
+          // TOCTOU guard: session may have been removed between the check above and here
+          if (!transport) {
+            if (this.isJsonRpcNotification(req.body)) {
+              logger.info('handleRequest: Session removed during lookup, accepting notification', { sessionId });
+              res.status(202).end();
+              return;
+            }
+            logger.warn('handleRequest: Session removed between check and use (TOCTOU)', { sessionId });
+            res.status(400).json({
+              jsonrpc: '2.0',
+              error: { code: -32000, message: 'Bad Request: Session not found or expired' },
+              id: req.body?.id || null,
+            });
+            return;
+          }
+
           // In multi-tenant shared mode, update instance context if provided
           const isMultiTenantEnabled = process.env.ENABLE_MULTI_TENANT === 'true';
           const sessionStrategy = process.env.MULTI_TENANT_SESSION_STRATEGY || 'instance';
@@ -627,7 +659,17 @@ export class SingleSessionHTTPServer {
           this.updateSessionAccess(sessionId);
           
         } else {
-          // Invalid request - no session ID and not an initialize request
+          // Notifications are fire-and-forget; returning 400 triggers reconnection storms (#654)
+          if (this.isJsonRpcNotification(req.body)) {
+            logger.info('handleRequest: Accepting notification for stale/missing session', {
+              method: req.body?.method,
+              sessionId: sessionId || 'none',
+            });
+            res.status(202).end();
+            return;
+          }
+
+          // Only return 400 for actual requests that need a valid session
           const errorDetails = {
             hasSessionId: !!sessionId,
             isInitialize: isInitialize,

src/mcp/handlers-n8n-manager.ts

@@ -2834,10 +2834,13 @@ export async function handleUpdateTable(args: unknown, context?: InstanceContext
     const client = ensureApiConfigured(context);
     const { tableId, name } = updateTableSchema.parse(args);
     const dataTable = await client.updateDataTable(tableId, { name });
+    const rawArgs = args as Record<string, unknown>;
+    const hasColumns = rawArgs && typeof rawArgs === 'object' && 'columns' in rawArgs;
     return {
       success: true,
       data: dataTable,
-      message: `Data table renamed to "${dataTable.name}"`,
+      message: `Data table renamed to "${dataTable.name}"` +
+        (hasColumns ? '. Note: columns parameter was ignored — table schema is immutable after creation via the public API' : ''),
     };
   } catch (error) {
     return handleDataTableError(error);

src/mcp/tool-docs/workflow_management/n8n-manage-datatable.ts

@@ -14,7 +14,7 @@ export const n8nManageDatatableDoc: ToolDocumentation = {
       'Use dryRun: true to preview update/upsert/delete before applying',
       'Filter supports: eq, neq, like, ilike, gt, gte, lt, lte conditions',
       'Use returnData: true to get affected rows back from update/upsert/delete',
-      'Requires n8n enterprise or cloud with data tables feature'
+      'Requires N8N_API_URL and N8N_API_KEY configured'
     ]
   },
   full: {
@@ -96,8 +96,6 @@ export const n8nManageDatatableDoc: ToolDocumentation = {
       'Use sortBy for deterministic row ordering',
     ],
     pitfalls: [
-      'Requires N8N_API_URL and N8N_API_KEY configured',
-      'Feature only available on n8n enterprise or cloud plans',
       'deleteTable permanently deletes all rows — cannot be undone',
       'deleteRows requires a filter — cannot delete all rows without one',
       'Column types cannot be changed after table creation via API',

src/mcp/tools-n8n-manager.ts

@@ -609,7 +609,7 @@ export const n8nManagementTools: ToolDefinition[] = [
   },
   {
     name: 'n8n_manage_datatable',
-    description: `Manage n8n data tables and rows. Actions: createTable, listTables, getTable, updateTable, deleteTable, getRows, insertRows, updateRows, upsertRows, deleteRows. Requires n8n enterprise/cloud with data tables feature.`,
+    description: `Manage n8n data tables and rows. Actions: createTable, listTables, getTable, updateTable, deleteTable, getRows, insertRows, updateRows, upsertRows, deleteRows.`,
     inputSchema: {
       type: 'object',
       properties: {
@@ -619,10 +619,10 @@ export const n8nManagementTools: ToolDefinition[] = [
           description: 'Operation to perform',
         },
         tableId: { type: 'string', description: 'Data table ID (required for all actions except createTable and listTables)' },
-        name: { type: 'string', description: 'For createTable/updateTable: table name' },
+        name: { type: 'string', description: 'For createTable: table name. For updateTable: new name (rename only — schema is immutable after creation)' },
         columns: {
           type: 'array',
-          description: 'For createTable: column definitions',
+          description: 'For createTable only: column definitions (schema is immutable after creation via public API)',
           items: {
             type: 'object',
             properties: {

src/services/n8n-validation.ts

@@ -1,3 +1,4 @@
+import crypto from 'crypto';
 import { z } from 'zod';
 import { WorkflowNode, WorkflowConnection, Workflow } from '../types/n8n-api';
 import { isTriggerNode, isActivatableTrigger } from '../utils/node-type-utils';
@@ -87,6 +88,22 @@ export function validateWorkflowSettings(settings: unknown): z.infer<typeof work
   return workflowSettingsSchema.parse(settings);
 }
 
+const WEBHOOK_NODE_TYPES = new Set([
+  'n8n-nodes-base.webhook',
+  'n8n-nodes-base.webhookTrigger',
+  'n8n-nodes-base.formTrigger',
+  '@n8n/n8n-nodes-langchain.chatTrigger',
+]);
+
+function ensureWebhookIds(nodes?: WorkflowNode[]): void {
+  if (!nodes) return;
+  for (const node of nodes) {
+    if (WEBHOOK_NODE_TYPES.has(node.type) && !node.webhookId) {
+      node.webhookId = crypto.randomUUID();
+    }
+  }
+}
+
 // Clean workflow data for API operations
 export function cleanWorkflowForCreate(workflow: Partial<Workflow>): Partial<Workflow> {
   const {
@@ -109,6 +126,8 @@ export function cleanWorkflowForCreate(workflow: Partial<Workflow>): Partial<Wor
     cleanedWorkflow.settings = defaultWorkflowSettings;
   }
 
+  ensureWebhookIds(cleanedWorkflow.nodes);
+
   return cleanedWorkflow;
 }
 
@@ -194,6 +213,8 @@ export function cleanWorkflowForUpdate(workflow: Workflow): Partial<Workflow> {
     cleanedWorkflow.settings = { executionOrder: 'v1' as const };
   }
 
+  ensureWebhookIds(cleanedWorkflow.nodes);
+
   return cleanedWorkflow;
 }
 

tests/unit/http-server-session-management.test.ts

@@ -219,6 +219,7 @@ describe('HTTP Server Session Management', () => {
       status: vi.fn().mockReturnThis(),
       json: vi.fn().mockReturnThis(),
       send: vi.fn().mockReturnThis(),
+      end: vi.fn().mockReturnThis(),
       setHeader: vi.fn((key: string, value: string) => {
         headers[key.toLowerCase()] = value;
       }),
@@ -1186,4 +1187,121 @@ describe('HTTP Server Session Management', () => {
       expect(sessionInfo.age).toBeGreaterThanOrEqual(0);
     });
   });
+
+  describe('Notification handling for stale sessions (#654)', () => {
+    beforeEach(() => {
+      // Re-apply mockImplementation after vi.clearAllMocks() resets it
+      mockConsoleManager.wrapOperation.mockImplementation(async (fn: () => Promise<any>) => {
+        return await fn();
+      });
+    });
+
+    it('should return 202 for notification with stale session ID', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+
+      req.headers = { 'mcp-session-id': 'stale-session-that-does-not-exist' };
+      req.method = 'POST';
+      req.body = {
+        jsonrpc: '2.0',
+        method: 'notifications/initialized',
+      };
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(202);
+      expect(res.end).toHaveBeenCalled();
+    });
+
+    it('should return 202 for notification batch with stale session ID', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+
+      req.headers = { 'mcp-session-id': 'stale-session-that-does-not-exist' };
+      req.method = 'POST';
+      req.body = [
+        { jsonrpc: '2.0', method: 'notifications/initialized' },
+        { jsonrpc: '2.0', method: 'notifications/cancelled' },
+      ];
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(202);
+      expect(res.end).toHaveBeenCalled();
+    });
+
+    it('should return 400 for request (with id) with stale session ID', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+      req.headers = { 'mcp-session-id': 'stale-session-that-does-not-exist' };
+      req.method = 'POST';
+      req.body = {
+        jsonrpc: '2.0',
+        method: 'tools/call',
+        params: { name: 'search_nodes', arguments: { query: 'http' } },
+        id: 42,
+      };
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(400);
+      expect(res.json).toHaveBeenCalledWith(expect.objectContaining({
+        error: expect.objectContaining({
+          message: 'Bad Request: Session not found or expired',
+        }),
+      }));
+    });
+
+    it('should return 202 for notification with no session ID', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+
+      req.method = 'POST';
+      req.body = {
+        jsonrpc: '2.0',
+        method: 'notifications/cancelled',
+      };
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(202);
+      expect(res.end).toHaveBeenCalled();
+    });
+
+    it('should return 400 for request with no session ID and not initialize', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+      req.method = 'POST';
+      req.body = {
+        jsonrpc: '2.0',
+        method: 'tools/list',
+        id: 1,
+      };
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(400);
+    });
+
+    it('should return 400 for mixed batch (notification + request) with stale session', async () => {
+      server = new SingleSessionHTTPServer();
+
+      const { req, res } = createMockReqRes();
+      req.headers = { 'mcp-session-id': 'stale-session-that-does-not-exist' };
+      req.method = 'POST';
+      req.body = [
+        { jsonrpc: '2.0', method: 'notifications/initialized' },
+        { jsonrpc: '2.0', method: 'tools/list', id: 1 },
+      ];
+
+      await server.handleRequest(req as any, res as any);
+
+      expect(res.status).toHaveBeenCalledWith(400);
+    });
+  });
 });

tests/unit/mcp/handlers-manage-datatable.test.ts

@@ -363,6 +363,22 @@ describe('Data Table Handlers (n8n_manage_datatable)', () => {
       expect(result.success).toBe(false);
       expect(result.error).toBe('Update failed');
     });
+
+    it('should warn when columns parameter is passed', async () => {
+      const updatedTable = { id: 'dt-1', name: 'Renamed' };
+      mockApiClient.updateDataTable.mockResolvedValue(updatedTable);
+
+      const result = await handlers.handleUpdateTable({
+        tableId: 'dt-1',
+        name: 'Renamed',
+        columns: [{ name: 'phone', type: 'string' }],
+      });
+
+      expect(result.success).toBe(true);
+      expect(result.message).toContain('columns parameter was ignored');
+      expect(result.message).toContain('immutable after creation');
+      expect(mockApiClient.updateDataTable).toHaveBeenCalledWith('dt-1', { name: 'Renamed' });
+    });
   });
 
   // ========================================================================

tests/unit/services/n8n-validation.test.ts

@@ -19,6 +19,14 @@ import { WorkflowBuilder } from '../../utils/builders/workflow.builder';
 import { z } from 'zod';
 import { WorkflowNode, WorkflowConnection, Workflow } from '../../../src/types/n8n-api';
 
+function webhookNode(id: string, name: string, type: string, typeVersion = 2): WorkflowNode {
+  return { id, name, type, typeVersion, position: [250, 300] as [number, number], parameters: {} };
+}
+
+function workflowWithNodes(nodes: WorkflowNode[]): Partial<Workflow> {
+  return { name: 'Test', nodes, connections: {} };
+}
+
 describe('n8n-validation', () => {
   describe('Zod Schemas', () => {
     describe('workflowNodeSchema', () => {
@@ -301,6 +309,44 @@ describe('n8n-validation', () => {
         const cleaned = cleanWorkflowForCreate(workflow as Workflow);
         expect(cleaned.settings).toEqual(customSettings);
       });
+
+      it('should inject webhookId on webhook nodes missing it', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Webhook', 'n8n-nodes-base.webhook'),
+        ]);
+
+        const cleaned = cleanWorkflowForCreate(workflow as Workflow);
+        expect(cleaned.nodes![0].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+      });
+
+      it('should preserve existing webhookId on webhook nodes', () => {
+        const workflow = workflowWithNodes([
+          { ...webhookNode('1', 'Webhook', 'n8n-nodes-base.webhook'), webhookId: 'existing-id' },
+        ]);
+
+        const cleaned = cleanWorkflowForCreate(workflow as Workflow);
+        expect(cleaned.nodes![0].webhookId).toBe('existing-id');
+      });
+
+      it('should inject webhookId on formTrigger and chatTrigger nodes', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Form', 'n8n-nodes-base.formTrigger'),
+          webhookNode('2', 'Chat', '@n8n/n8n-nodes-langchain.chatTrigger'),
+        ]);
+
+        const cleaned = cleanWorkflowForCreate(workflow as Workflow);
+        expect(cleaned.nodes![0].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+        expect(cleaned.nodes![1].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+      });
+
+      it('should not inject webhookId on non-webhook nodes', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Set', 'n8n-nodes-base.set', 3.4),
+        ]);
+
+        const cleaned = cleanWorkflowForCreate(workflow as Workflow);
+        expect(cleaned.nodes![0].webhookId).toBeUndefined();
+      });
     });
 
     describe('cleanWorkflowForUpdate', () => {
@@ -533,6 +579,44 @@ describe('n8n-validation', () => {
         });
         expect(cleaned.settings).not.toHaveProperty('someOtherProperty');
       });
+
+      it('should inject webhookId on webhook nodes missing it', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Webhook', 'n8n-nodes-base.webhook'),
+        ]) as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        expect(cleaned.nodes![0].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+      });
+
+      it('should preserve existing webhookId on webhook nodes', () => {
+        const workflow = workflowWithNodes([
+          { ...webhookNode('1', 'Webhook', 'n8n-nodes-base.webhook'), webhookId: 'existing-id' },
+        ]) as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        expect(cleaned.nodes![0].webhookId).toBe('existing-id');
+      });
+
+      it('should inject webhookId on formTrigger and chatTrigger nodes', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Form', 'n8n-nodes-base.formTrigger'),
+          webhookNode('2', 'Chat', '@n8n/n8n-nodes-langchain.chatTrigger'),
+        ]) as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        expect(cleaned.nodes![0].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+        expect(cleaned.nodes![1].webhookId).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-/);
+      });
+
+      it('should not inject webhookId on non-webhook nodes', () => {
+        const workflow = workflowWithNodes([
+          webhookNode('1', 'Set', 'n8n-nodes-base.set', 3.4),
+        ]) as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        expect(cleaned.nodes![0].webhookId).toBeUndefined();
+      });
     });
   });