fix: comprehensive param type coercion for Claude Desktop/Claude.ai (#605) (#609)

Expand coerceStringifiedJsonParams() to handle ALL type mismatches,
not just stringified objects/arrays. Testing showed 6/9 tools still
failing in Claude Desktop after v2.35.4.

- Coerce string→number, string→boolean, number→string, boolean→string
- Add safeguard for entire args object arriving as JSON string
- Add [Diagnostic] section to error responses with received arg types
- Bump to v2.35.5
- 24 unit tests (9 new)

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

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

CHANGELOG.md

@@ -7,6 +7,32 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.35.5] - 2026-02-22
+
+### Fixed
+
+- **Comprehensive parameter type coercion for Claude Desktop / Claude.ai** (Issue #605): Expanded the v2.35.4 fix to handle ALL type mismatches, not just stringified objects/arrays. Testing revealed 6/9 tools still failing in Claude Desktop after the initial fix.
+  - Extended `coerceStringifiedJsonParams()` to coerce every schema type: `string→number`, `string→boolean`, `number→string`, `boolean→string` (in addition to existing `string→object` and `string→array`)
+  - Added top-level safeguard to parse the entire `args` object if it arrives as a JSON string
+  - Added `[Diagnostic]` section to error responses showing received argument types, enabling users to report exactly what their MCP client sends
+  - Added 9 new unit tests (24 total) covering number, boolean, and number-to-string coercion
+
+Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en
+
+## [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

dist/mcp/server.d.ts

@@ -30,6 +30,7 @@ export declare class N8NDocumentationMCPServer {
     private validateToolParams;
     private validateToolParamsBasic;
     private validateExtractedArgs;
+    private coerceStringifiedJsonParams;
     private listNodes;
     private getNodeInfo;
     private searchNodes;

dist/mcp/server.d.ts.map

@@ -1 +1 @@
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+{"version":3,"file":"server.d.ts","sourceRoot":"","sources":["../../src/mcp/server.ts"],"names":[],"mappings":"AA0CA,OAAO,EAAE,eAAe,EAAE,MAAM,2BAA2B,CAAC;AAE5D,OAAO,EAAE,gBAAgB,EAAE,MAAM,iCAAiC,CAAC;AAmGnE,qBAAa,yBAAyB;IACpC,OAAO,CAAC,MAAM,CAAS;IACvB,OAAO,CAAC,EAAE,CAAgC;IAC1C,OAAO,CAAC,UAAU,CAA+B;IACjD,OAAO,CAAC,eAAe,CAAgC;IACvD,OAAO,CAAC,WAAW,CAAgB;IACnC,OAAO,CAAC,KAAK,CAAqB;IAClC,OAAO,CAAC,UAAU,CAAa;IAC/B,OAAO,CAAC,eAAe,CAAC,CAAkB;IAC1C,OAAO,CAAC,YAAY,CAAuB;IAC3C,OAAO,CAAC,qBAAqB,CAAsB;IACnD,OAAO,CAAC,WAAW,CAAiC;IACpD,OAAO,CAAC,kBAAkB,CAA4B;IACtD,OAAO,CAAC,iBAAiB,CAAkB;IAC3C,OAAO,CAAC,aAAa,CAAoC;IACzD,OAAO,CAAC,UAAU,CAAkB;gBAExB,eAAe,CAAC,EAAE,eAAe,EAAE,WAAW,CAAC,EAAE,gBAAgB;IAuGvE,KAAK,IAAI,OAAO,CAAC,IAAI,CAAC;YA+Cd,kBAAkB;YAiDlB,wBAAwB;IA0BtC,OAAO,CAAC,kBAAkB;YA6CZ,iBAAiB;IAa/B,OAAO,CAAC,eAAe,CAAkB;YAE3B,sBAAsB;IAgDpC,OAAO,CAAC,gBAAgB;IAqCxB,OAAO,CAAC,aAAa;IA0XrB,OAAO,CAAC,wBAAwB;IAoFhC,OAAO,CAAC,kBAAkB;IAqE1B,OAAO,CAAC,uBAAuB;IAwB/B,OAAO,CAAC,qBAAqB;IAiF7B,OAAO,CAAC,2BAA2B;YA0UrB,SAAS;YA2DT,WAAW;YAkFX,WAAW;YA0CX,cAAc;YA8Md,gBAAgB;IAqD9B,OAAO,CAAC,mBAAmB;IAwE3B,OAAO,CAAC,eAAe;YAsBT,eAAe;IA2L7B,OAAO,CAAC,kBAAkB;IAQ1B,OAAO,CAAC,uBAAuB;IA0D/B,OAAO,CAAC,iBAAiB;YAqFX,WAAW;YAgCX,oBAAoB;IAuFlC,OAAO,CAAC,aAAa;YAQP,qBAAqB;YAwDrB,iBAAiB;YAiKjB,OAAO;YAgDP,cAAc;YAwFd,iBAAiB;IAqC/B,OAAO,CAAC,iBAAiB;IA0BzB,OAAO,CAAC,iBAAiB;IA0BzB,OAAO,CAAC,eAAe;IAwCvB,OAAO,CAAC,kBAAkB;IAiC1B,OAAO,CAAC,aAAa;IAoCrB,OAAO,CAAC,0BAA0B;IAgClC,OAAO,CAAC,4BAA4B;YAKtB,oBAAoB;IAsDlC,OAAO,CAAC,gBAAgB;YAiBV,SAAS;YA6CT,kBAAkB;YAqElB,uBAAuB;YAsDvB,iBAAiB;IAqE/B,OAAO,CAAC,qBAAqB;IA8C7B,OAAO,CAAC,uBAAuB;IA4D/B,OAAO,CAAC,wBAAwB;IAkChC,OAAO,CAAC,iBAAiB;YAoDX,mBAAmB;YAoEnB,qBAAqB;IAS7B,OAAO,CAAC,SAAS,EAAE,GAAG,GAAG,OAAO,CAAC,IAAI,CAAC;YAS9B,aAAa;YAcb,iBAAiB;YAoBjB,WAAW;YAwBX,eAAe;YAqBf,mBAAmB;YAwBnB,yBAAyB;IA4CvC,OAAO,CAAC,kBAAkB;YAiBZ,gBAAgB;YA6HhB,2BAA2B;YAiE3B,2BAA2B;IAyEnC,GAAG,IAAI,OAAO,CAAC,IAAI,CAAC;IA0BpB,QAAQ,IAAI,OAAO,CAAC,IAAI,CAAC;CAgEhC"}

dist/mcp/server.js

@@ -457,6 +457,18 @@ class N8NDocumentationMCPServer {
                 };
             }
             let processedArgs = args;
+            if (typeof args === 'string') {
+                try {
+                    const parsed = JSON.parse(args);
+                    if (parsed && typeof parsed === 'object' && !Array.isArray(parsed)) {
+                        processedArgs = parsed;
+                        logger_1.logger.warn(`Coerced stringified args object for tool "${name}"`);
+                    }
+                }
+                catch {
+                    logger_1.logger.warn(`Tool "${name}" received string args that are not valid JSON`);
+                }
+            }
             if (args && typeof args === 'object' && 'output' in args) {
                 try {
                     const possibleNestedData = args.output;
@@ -485,6 +497,7 @@ class N8NDocumentationMCPServer {
                     });
                 }
             }
+            processedArgs = this.coerceStringifiedJsonParams(name, processedArgs);
             try {
                 logger_1.logger.debug(`Executing tool: ${name}`, { args: processedArgs });
                 const startTime = Date.now();
@@ -556,6 +569,13 @@ class N8NDocumentationMCPServer {
                 if (name.startsWith('validate_') && (errorMessage.includes('config') || errorMessage.includes('nodeType'))) {
                     helpfulMessage += '\n\nFor validation tools:\n- nodeType should be a string (e.g., "nodes-base.webhook")\n- config should be an object (e.g., {})';
                 }
+                try {
+                    const argDiag = processedArgs && typeof processedArgs === 'object'
+                        ? Object.entries(processedArgs).map(([k, v]) => `${k}: ${typeof v}`).join(', ')
+                        : `args type: ${typeof processedArgs}`;
+                    helpfulMessage += `\n\n[Diagnostic] Received arg types: {${argDiag}}`;
+                }
+                catch { }
                 return {
                     content: [
                         {
@@ -795,6 +815,93 @@ class N8NDocumentationMCPServer {
         }
         return true;
     }
+    coerceStringifiedJsonParams(toolName, args) {
+        if (!args || typeof args !== 'object')
+            return args;
+        const allTools = [...tools_1.n8nDocumentationToolsFinal, ...tools_n8n_manager_1.n8nManagementTools];
+        const tool = allTools.find(t => t.name === toolName);
+        if (!tool?.inputSchema?.properties)
+            return args;
+        const properties = tool.inputSchema.properties;
+        const coerced = { ...args };
+        let coercedAny = false;
+        for (const [key, value] of Object.entries(coerced)) {
+            if (value === undefined || value === null)
+                continue;
+            const propSchema = properties[key];
+            if (!propSchema)
+                continue;
+            const expectedType = propSchema.type;
+            if (!expectedType)
+                continue;
+            const actualType = typeof value;
+            if (expectedType === 'string' && actualType === 'string')
+                continue;
+            if ((expectedType === 'number' || expectedType === 'integer') && actualType === 'number')
+                continue;
+            if (expectedType === 'boolean' && actualType === 'boolean')
+                continue;
+            if (expectedType === 'object' && actualType === 'object' && !Array.isArray(value))
+                continue;
+            if (expectedType === 'array' && Array.isArray(value))
+                continue;
+            if (actualType === 'string') {
+                const trimmed = value.trim();
+                if (expectedType === 'object' && trimmed.startsWith('{')) {
+                    try {
+                        const parsed = JSON.parse(trimmed);
+                        if (typeof parsed === 'object' && parsed !== null && !Array.isArray(parsed)) {
+                            coerced[key] = parsed;
+                            coercedAny = true;
+                        }
+                    }
+                    catch { }
+                    continue;
+                }
+                if (expectedType === 'array' && trimmed.startsWith('[')) {
+                    try {
+                        const parsed = JSON.parse(trimmed);
+                        if (Array.isArray(parsed)) {
+                            coerced[key] = parsed;
+                            coercedAny = true;
+                        }
+                    }
+                    catch { }
+                    continue;
+                }
+                if (expectedType === 'number' || expectedType === 'integer') {
+                    const num = Number(trimmed);
+                    if (!isNaN(num) && trimmed !== '') {
+                        coerced[key] = expectedType === 'integer' ? Math.trunc(num) : num;
+                        coercedAny = true;
+                    }
+                    continue;
+                }
+                if (expectedType === 'boolean') {
+                    if (trimmed === 'true') {
+                        coerced[key] = true;
+                        coercedAny = true;
+                    }
+                    else if (trimmed === 'false') {
+                        coerced[key] = false;
+                        coercedAny = true;
+                    }
+                    continue;
+                }
+            }
+            if (expectedType === 'string' && (actualType === 'number' || actualType === 'boolean')) {
+                coerced[key] = String(value);
+                coercedAny = true;
+                continue;
+            }
+        }
+        if (coercedAny) {
+            logger_1.logger.warn(`Coerced mistyped params for tool "${toolName}"`, {
+                original: Object.fromEntries(Object.entries(args).map(([k, v]) => [k, `${typeof v}: ${typeof v === 'string' ? v.substring(0, 80) : v}`])),
+            });
+        }
+        return coerced;
+    }
     async executeTool(name, args) {
         args = args || {};
         const disabledTools = this.getDisabledTools();

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.35.3",
+  "version": "2.35.5",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/mcp/server.ts

@@ -687,9 +687,23 @@ export class N8NDocumentationMCPServer {
         };
       }
 
+      // Safeguard: if the entire args object arrives as a JSON string, parse it.
+      // Some MCP clients may serialize the arguments object itself.
+      let processedArgs: Record<string, any> | undefined = args;
+      if (typeof args === 'string') {
+        try {
+          const parsed = JSON.parse(args as unknown as string);
+          if (parsed && typeof parsed === 'object' && !Array.isArray(parsed)) {
+            processedArgs = parsed;
+            logger.warn(`Coerced stringified args object for tool "${name}"`);
+          }
+        } catch {
+          logger.warn(`Tool "${name}" received string args that are not valid JSON`);
+        }
+      }
+
       // Workaround for n8n's nested output bug
       // Check if args contains nested 'output' structure from n8n's memory corruption
-      let processedArgs = args;
       if (args && typeof args === 'object' && 'output' in args) {
         try {
           const possibleNestedData = args.output;
@@ -721,6 +735,12 @@ export class N8NDocumentationMCPServer {
         }
       }
 
+      // Workaround for Claude Desktop / Claude.ai MCP client bugs that
+      // serialize parameters with wrong types. Coerces ALL mismatched types
+      // (string↔object, string↔number, string↔boolean, etc.) using the
+      // tool's inputSchema as the source of truth.
+      processedArgs = this.coerceStringifiedJsonParams(name, processedArgs);
+
       try {
         logger.debug(`Executing tool: ${name}`, { args: processedArgs });
         const startTime = Date.now();
@@ -822,6 +842,14 @@ export class N8NDocumentationMCPServer {
           helpfulMessage += '\n\nFor validation tools:\n- nodeType should be a string (e.g., "nodes-base.webhook")\n- config should be an object (e.g., {})';
         }
 
+        // Include diagnostic info about received args to help debug client issues
+        try {
+          const argDiag = processedArgs && typeof processedArgs === 'object'
+            ? Object.entries(processedArgs).map(([k, v]) => `${k}: ${typeof v}`).join(', ')
+            : `args type: ${typeof processedArgs}`;
+          helpfulMessage += `\n\n[Diagnostic] Received arg types: {${argDiag}}`;
+        } catch { /* ignore diagnostic errors */ }
+
         return {
           content: [
             {
@@ -1125,6 +1153,109 @@ export class N8NDocumentationMCPServer {
     return true;
   }
 
+  /**
+   * Coerce mistyped parameters back to their expected types.
+   * Workaround for Claude Desktop / Claude.ai MCP client bugs that serialize
+   * parameters incorrectly (objects as strings, numbers as strings, etc.).
+   *
+   * Handles ALL type mismatches based on the tool's inputSchema:
+   *   string→object, string→array   : JSON.parse
+   *   string→number, string→integer : Number()
+   *   string→boolean                : "true"/"false" parsing
+   *   number→string, boolean→string : .toString()
+   */
+  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 };
+    let coercedAny = false;
+
+    for (const [key, value] of Object.entries(coerced)) {
+      if (value === undefined || value === null) continue;
+
+      const propSchema = (properties as any)[key];
+      if (!propSchema) continue;
+      const expectedType = propSchema.type;
+      if (!expectedType) continue;
+
+      const actualType = typeof value;
+
+      // Already correct type — skip
+      if (expectedType === 'string' && actualType === 'string') continue;
+      if ((expectedType === 'number' || expectedType === 'integer') && actualType === 'number') continue;
+      if (expectedType === 'boolean' && actualType === 'boolean') continue;
+      if (expectedType === 'object' && actualType === 'object' && !Array.isArray(value)) continue;
+      if (expectedType === 'array' && Array.isArray(value)) continue;
+
+      // --- Coercion: string value → expected type ---
+      if (actualType === 'string') {
+        const trimmed = (value as string).trim();
+
+        if (expectedType === 'object' && trimmed.startsWith('{')) {
+          try {
+            const parsed = JSON.parse(trimmed);
+            if (typeof parsed === 'object' && parsed !== null && !Array.isArray(parsed)) {
+              coerced[key] = parsed;
+              coercedAny = true;
+            }
+          } catch { /* keep original */ }
+          continue;
+        }
+
+        if (expectedType === 'array' && trimmed.startsWith('[')) {
+          try {
+            const parsed = JSON.parse(trimmed);
+            if (Array.isArray(parsed)) {
+              coerced[key] = parsed;
+              coercedAny = true;
+            }
+          } catch { /* keep original */ }
+          continue;
+        }
+
+        if (expectedType === 'number' || expectedType === 'integer') {
+          const num = Number(trimmed);
+          if (!isNaN(num) && trimmed !== '') {
+            coerced[key] = expectedType === 'integer' ? Math.trunc(num) : num;
+            coercedAny = true;
+          }
+          continue;
+        }
+
+        if (expectedType === 'boolean') {
+          if (trimmed === 'true') { coerced[key] = true; coercedAny = true; }
+          else if (trimmed === 'false') { coerced[key] = false; coercedAny = true; }
+          continue;
+        }
+      }
+
+      // --- Coercion: number/boolean value → expected string ---
+      if (expectedType === 'string' && (actualType === 'number' || actualType === 'boolean')) {
+        coerced[key] = String(value);
+        coercedAny = true;
+        continue;
+      }
+    }
+
+    if (coercedAny) {
+      logger.warn(`Coerced mistyped params for tool "${toolName}"`, {
+        original: Object.fromEntries(
+          Object.entries(args).map(([k, v]) => [k, `${typeof v}: ${typeof v === 'string' ? v.substring(0, 80) : v}`])
+        ),
+      });
+    }
+
+    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 +1,300 @@
+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('Number coercion', () => {
+    it('should coerce string to number for search_nodes limit', () => {
+      const args = {
+        query: 'webhook',
+        limit: '10'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.limit).toBe(10);
+      expect(result.query).toBe('webhook');
+    });
+
+    it('should coerce string to number for n8n_executions limit', () => {
+      const args = {
+        action: 'list',
+        limit: '50'
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_executions', args);
+      expect(result.limit).toBe(50);
+    });
+
+    it('should not coerce non-numeric string to number', () => {
+      const args = {
+        query: 'webhook',
+        limit: 'abc'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.limit).toBe('abc');
+    });
+  });
+
+  describe('Boolean coercion', () => {
+    it('should coerce "true" string to boolean', () => {
+      const args = {
+        query: 'webhook',
+        includeExamples: 'true'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.includeExamples).toBe(true);
+    });
+
+    it('should coerce "false" string to boolean', () => {
+      const args = {
+        query: 'webhook',
+        includeExamples: 'false'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.includeExamples).toBe(false);
+    });
+
+    it('should not coerce non-boolean string to boolean', () => {
+      const args = {
+        query: 'webhook',
+        includeExamples: 'yes'
+      };
+      const result = server.testCoerceStringifiedJsonParams('search_nodes', args);
+      expect(result.includeExamples).toBe('yes');
+    });
+  });
+
+  describe('Number-to-string coercion', () => {
+    it('should coerce number to string for n8n_get_workflow id', () => {
+      const args = {
+        id: 123,
+        mode: 'minimal'
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_get_workflow', args);
+      expect(result.id).toBe('123');
+      expect(result.mode).toBe('minimal');
+    });
+
+    it('should coerce boolean to string when string expected', () => {
+      const args = {
+        id: true
+      };
+      const result = server.testCoerceStringifiedJsonParams('n8n_get_workflow', args);
+      expect(result.id).toBe('true');
+    });
+  });
+
+  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);
+    });
+
+    it('should handle mixed type mismatches from Claude Desktop', () => {
+      // Simulate Claude Desktop sending object params as strings
+      const args = {
+        nodeType: 'nodes-base.httpRequest',
+        config: '{"method":"GET","url":"https://example.com"}',
+        mode: 'full',
+        profile: 'ai-friendly'
+      };
+      const result = server.testCoerceStringifiedJsonParams('validate_node', args);
+      expect(result.config).toEqual({ method: 'GET', url: 'https://example.com' });
+      expect(result.nodeType).toBe('nodes-base.httpRequest');
+      expect(result.mode).toBe('full');
+    });
+  });
+});