fix: defensive JSON.parse for stringified object/array params (#605) (#606)

* chore: update n8n to 2.8.3 and bump version to 2.35.3

- Updated n8n from 2.6.3 to 2.8.3
- Updated n8n-core from 2.6.1 to 2.8.1
- Updated n8n-workflow from 2.6.0 to 2.8.0
- Updated @n8n/n8n-nodes-langchain from 2.6.2 to 2.8.1
- Fixed node loader to bypass restricted package.json exports in
  @n8n/n8n-nodes-langchain >=2.9.0 (resolves via absolute paths)
- Fixed community doc generator for cloud LLMs: added API key env var
  support, switched to max_completion_tokens, auto-omit temperature
- Rebuilt node database with 1,236 nodes (673 n8n-nodes-base,
  133 @n8n/n8n-nodes-langchain, 430 community)
- Refreshed community nodes (361 verified + 69 npm) with 424 AI summaries
- Updated README badge with new n8n version and node counts
- Updated CHANGELOG with dependency changes

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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: update documentation-generator tests for max_completion_tokens

- Updated test assertions from max_tokens to max_completion_tokens
- Updated testConnection token limit expectation from 10 to 200
- Added temperature to test config to match new configurable behavior

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: defensive JSON.parse for stringified object/array params (#605)

Claude Desktop 1.1.3189 serializes object/array MCP parameters as JSON
strings, causing ZodError failures for ~60% of tools. Add schema-driven
coercion in the central CallToolRequestSchema handler to detect and parse
them back automatically.

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

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.35.4] - 2026-02-20
+
+### Fixed
+
+- **Defensive JSON.parse for stringified object/array parameters** (Issue #605): Claude Desktop 1.1.3189 serializes JSON object/array MCP parameters as strings, causing ZodError failures for ~60% of tools that accept nested parameters
+  - Added schema-driven `coerceStringifiedJsonParams()` in the central `CallToolRequestSchema` handler
+  - Automatically detects string values where the tool's `inputSchema` expects `object` or `array`, and parses them back
+  - Safe: prefix check before parsing, type verification after, try/catch preserves original on failure
+  - No-op for correct clients: native objects pass through unchanged
+  - Affects 9 tools with object/array params: `validate_node`, `validate_workflow`, `n8n_create_workflow`, `n8n_update_full_workflow`, `n8n_update_partial_workflow`, `n8n_validate_workflow`, `n8n_autofix_workflow`, `n8n_test_workflow`, `n8n_executions`
+  - Added 15 unit tests covering coercion, no-op, safety, and end-to-end scenarios
+
+Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en
+
 ## [2.35.3] - 2026-02-19
 
 ### Changed

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.35.3",
+  "version": "2.35.4",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/mcp/server.ts

@@ -721,6 +721,11 @@ export class N8NDocumentationMCPServer {
         }
       }
 
+      // Workaround for Claude Desktop 1.1.3189 string serialization bug.
+      // The MCP client serializes object/array parameters as JSON strings.
+      // Use the tool's inputSchema to detect and parse them back.
+      processedArgs = this.coerceStringifiedJsonParams(name, processedArgs);
+
       try {
         logger.debug(`Executing tool: ${name}`, { args: processedArgs });
         const startTime = Date.now();
@@ -1125,6 +1130,50 @@ export class N8NDocumentationMCPServer {
     return true;
   }
 
+  /**
+   * Coerce stringified JSON parameters back to objects/arrays.
+   * Workaround for Claude Desktop 1.1.3189 which serializes object/array
+   * params as JSON strings before sending them to MCP servers.
+   */
+  private coerceStringifiedJsonParams(
+    toolName: string,
+    args: Record<string, any> | undefined
+  ): Record<string, any> | undefined {
+    if (!args || typeof args !== 'object') return args;
+
+    const allTools = [...n8nDocumentationToolsFinal, ...n8nManagementTools];
+    const tool = allTools.find(t => t.name === toolName);
+    if (!tool?.inputSchema?.properties) return args;
+
+    const properties = tool.inputSchema.properties;
+    const coerced = { ...args };
+
+    for (const [key, value] of Object.entries(coerced)) {
+      if (typeof value !== 'string') continue;
+      const expectedType = (properties as any)[key]?.type;
+      if (expectedType !== 'object' && expectedType !== 'array') continue;
+
+      const trimmed = value.trim();
+      const validPrefix = (expectedType === 'object' && trimmed.startsWith('{'))
+                       || (expectedType === 'array'  && trimmed.startsWith('['));
+      if (!validPrefix) continue;
+
+      try {
+        const parsed = JSON.parse(trimmed);
+        const isArray = Array.isArray(parsed);
+        if ((expectedType === 'object' && typeof parsed === 'object' && !isArray)
+         || (expectedType === 'array'  && isArray)) {
+          coerced[key] = parsed;
+          logger.warn(`Coerced stringified ${expectedType} param "${key}" for tool "${toolName}"`);
+        }
+      } catch {
+        // Not valid JSON — keep original string, downstream validation will report the error
+      }
+    }
+
+    return coerced;
+  }
+
   async executeTool(name: string, args: any): Promise<any> {
     // Ensure args is an object and validate it
     args = args || {};

tests/unit/mcp/coerce-stringified-params.test.ts

@@ -0,0 +1,207 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { N8NDocumentationMCPServer } from '../../../src/mcp/server';
+
+// Mock the database and dependencies
+vi.mock('../../../src/database/database-adapter');
+vi.mock('../../../src/database/node-repository');
+vi.mock('../../../src/templates/template-service');
+vi.mock('../../../src/utils/logger');
+
+class TestableN8NMCPServer extends N8NDocumentationMCPServer {
+  public testCoerceStringifiedJsonParams(
+    toolName: string,
+    args: Record<string, any>
+  ): Record<string, any> {
+    return (this as any).coerceStringifiedJsonParams(toolName, args);
+  }
+}
+
+describe('coerceStringifiedJsonParams', () => {
+  let server: TestableN8NMCPServer;
+
+  beforeEach(() => {
+    process.env.NODE_DB_PATH = ':memory:';
+    server = new TestableN8NMCPServer();
+  });
+
+  afterEach(() => {
+    delete process.env.NODE_DB_PATH;
+  });
+
+  describe('Object coercion', () => {
+    it('should coerce stringified object for validate_node config', () => {
+      const args = {
+        nodeType: 'nodes-base.slack',
+        config: '{"resource":"channel","operation":"create"}'
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_node', args);
+      expect(result.config).toEqual({ resource: 'channel', operation: 'create' });
+      expect(result.nodeType).toBe('nodes-base.slack');
+    });
+
+    it('should coerce stringified object for n8n_create_workflow connections', () => {
+      const connections = { 'Webhook': { main: [[{ node: 'Slack', type: 'main', index: 0 }]] } };
+      const args = {
+        name: 'Test Workflow',
+        nodes: [{ id: '1', name: 'Webhook', type: 'n8n-nodes-base.webhook' }],
+        connections: JSON.stringify(connections)
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_create_workflow', args);
+      expect(result.connections).toEqual(connections);
+    });
+
+    it('should coerce stringified object for validate_workflow workflow param', () => {
+      const workflow = { nodes: [], connections: {} };
+      const args = {
+        workflow: JSON.stringify(workflow)
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_workflow', args);
+      expect(result.workflow).toEqual(workflow);
+    });
+  });
+
+  describe('Array coercion', () => {
+    it('should coerce stringified array for n8n_update_partial_workflow operations', () => {
+      const operations = [
+        { type: 'addNode', node: { id: '1', name: 'Test', type: 'n8n-nodes-base.noOp' } }
+      ];
+      const args = {
+        id: '123',
+        operations: JSON.stringify(operations)
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_update_partial_workflow', args);
+      expect(result.operations).toEqual(operations);
+      expect(result.id).toBe('123');
+    });
+
+    it('should coerce stringified array for n8n_autofix_workflow fixTypes', () => {
+      const fixTypes = ['expression-format', 'typeversion-correction'];
+      const args = {
+        id: '456',
+        fixTypes: JSON.stringify(fixTypes)
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_autofix_workflow', args);
+      expect(result.fixTypes).toEqual(fixTypes);
+    });
+  });
+
+  describe('No-op cases', () => {
+    it('should not modify object params that are already objects', () => {
+      const config = { resource: 'channel', operation: 'create' };
+      const args = {
+        nodeType: 'nodes-base.slack',
+        config
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_node', args);
+      expect(result.config).toEqual(config);
+      expect(result.config).toBe(config); // same reference
+    });
+
+    it('should not modify string params even if they contain JSON', () => {
+      const args = {
+        query: '{"some":"json"}',
+        limit: 10
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.query).toBe('{"some":"json"}');
+    });
+
+    it('should not modify args for tools with no object/array params', () => {
+      const args = {
+        query: 'webhook',
+        limit: 20,
+        mode: 'OR'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result).toEqual(args);
+    });
+  });
+
+  describe('Safety cases', () => {
+    it('should keep original string for invalid JSON', () => {
+      const args = {
+        nodeType: 'nodes-base.slack',
+        config: '{invalid json here}'
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_node', args);
+      expect(result.config).toBe('{invalid json here}');
+    });
+
+    it('should not attempt parse when object param starts with [', () => {
+      const args = {
+        nodeType: 'nodes-base.slack',
+        config: '[1, 2, 3]'
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_node', args);
+      expect(result.config).toBe('[1, 2, 3]');
+    });
+
+    it('should not attempt parse when array param starts with {', () => {
+      const args = {
+        id: '123',
+        operations: '{"not":"an array"}'
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_update_partial_workflow', args);
+      expect(result.operations).toBe('{"not":"an array"}');
+    });
+
+    it('should handle null args gracefully', () => {
+      const result = server.testCoerceStringifiedJsonParams('validate_node', null as any);
+      expect(result).toBeNull();
+    });
+
+    it('should handle undefined args gracefully', () => {
+      const result = server.testCoerceStringifiedJsonParams('validate_node', undefined as any);
+      expect(result).toBeUndefined();
+    });
+
+    it('should return args unchanged for unknown tool', () => {
+      const args = { config: '{"key":"value"}' };
+      const result = server.testCoerceStringifiedJsonParams('nonexistent_tool', args);
+      expect(result).toEqual(args);
+      expect(result.config).toBe('{"key":"value"}');
+    });
+  });
+
+  describe('End-to-end Claude Desktop scenario', () => {
+    it('should coerce all stringified params for n8n_create_workflow', () => {
+      const nodes = [
+        {
+          id: 'webhook_1',
+          name: 'Webhook',
+          type: 'n8n-nodes-base.webhook',
+          typeVersion: 1,
+          position: [250, 300],
+          parameters: { httpMethod: 'POST', path: 'slack-notify' }
+        },
+        {
+          id: 'slack_1',
+          name: 'Slack',
+          type: 'n8n-nodes-base.slack',
+          typeVersion: 1,
+          position: [450, 300],
+          parameters: { resource: 'message', operation: 'post', channel: '#general' }
+        }
+      ];
+      const connections = {
+        'Webhook': { main: [[{ node: 'Slack', type: 'main', index: 0 }]] }
+      };
+      const settings = { executionOrder: 'v1', timezone: 'America/New_York' };
+
+      // Simulate Claude Desktop sending all object/array params as strings
+      const args = {
+        name: 'Webhook to Slack',
+        nodes: JSON.stringify(nodes),
+        connections: JSON.stringify(connections),
+        settings: JSON.stringify(settings)
+      };
+
+      const result = server.testCoerceStringifiedJsonParams('n8n_create_workflow', args);
+
+      expect(result.name).toBe('Webhook to Slack');
+      expect(result.nodes).toEqual(nodes);
+      expect(result.connections).toEqual(connections);
+      expect(result.settings).toEqual(settings);
+    });
+  });
+});