Google Calendar MCP

# Example: MCP Server Review **Project:** Google Calendar MCP Server **Review Date:** October 2025 **Research Tool:** mcp-research skill --- ## MCP Compliance Findings ### Protocol Compliance ✅ **Status:** Compliant with JSON-RPC 2.0 and MCP spec 2025-06-18 **Validated:** - ✅ All messages include `jsonrpc: "2.0"` - ✅ Responses use `result` XOR `error` pattern - ✅ Initialization sequence correct (`initialize` → response → `initialized`) - ✅ Error codes appropriate (-32xxx for protocol errors) - ✅ Capabilities accurately declared **Transport:** stdio (newline-delimited JSON-RPC) - ✅ Logging to stderr only - ✅ Output flushed after each message - ✅ Handles EOF gracefully ### Capabilities ✅ **Declared in `initialize` response:** ```json { "protocolVersion": "2025-06-18", "capabilities": { "tools": {}, "resources": {}, "logging": {} }, "serverInfo": { "name": "google-calendar-mcp", "version": "2.0.6" } } ``` **Implemented:** - 15 tools (list-events, create-event, update-event, etc.) - 0 resources (opportunity for improvement) - 0 prompts (opportunity for improvement) **Recommendation:** Consider adding resources for common calendar views (`calendar://events/today`) and prompts for scheduling workflows. ### Security & Consent ⚠️ **Current Implementation:** - ✅ OAuth 2.0 authentication with refresh tokens - ✅ No hardcoded credentials (uses `GOOGLE_OAUTH_CREDENTIALS` env var) - ✅ Input validation via Zod schemas - ⚠️ **Missing:** Explicit user consent workflow for tool execution **Issue:** Tools execute immediately without consent prompt **Impact:** Violates MCP security requirement for user approval **Fix:** Implement consent check before tool execution: ```typescript // Add to BaseToolHandler async runToolWithConsent(args, oauth2Client) { // 1. Check if user consent granted for this tool const hasConsent = await this.checkUserConsent(this.toolName); if (!hasConsent) { throw new McpError( ErrorCode.InvalidRequest, 'User consent required for tool execution' ); } // 2. Execute tool return this.runTool(args, oauth2Client); } ``` **Reference:** See `references/common-pitfalls.md` → "Missing Consent Workflows" ### Tool Implementation ✅ **Pattern Compliance:** - ✅ `tools/list` returns complete tool definitions with JSON schemas - ✅ `tools/call` validates inputs against schemas - ✅ Results use proper content types (`text` with JSON.stringify) - ✅ Errors include actionable context **Example (create-event tool):** ```json { "name": "create-event", "description": "Creates a new calendar event", "inputSchema": { "type": "object", "properties": { "calendarId": { "type": "string" }, "summary": { "type": "string" }, "startTime": { "type": "string" } // ... more fields }, "required": ["calendarId", "summary", "startTime"] } } ``` **Best Practice:** Comprehensive schemas with clear descriptions ✅ ### Error Handling ✅ **Validated:** - ✅ Uses `McpError` from SDK - ✅ Standard JSON-RPC error codes for protocol errors - ✅ Custom codes for Google API errors (mapped appropriately) - ✅ Error messages are actionable with context **Example:** ```typescript // src/handlers/core/BaseToolHandler.ts handleGoogleApiError(error) { if (error.response?.status === 404) { throw new McpError(ErrorCode.InvalidRequest, 'Event not found'); } // ... more error mappings } ``` **Reference:** Follows patterns from `protocol-patterns.md` → "Error Handling" ### Performance ✅ **Current Optimization:** - ✅ OAuth client reused (not recreated per request) - ✅ Timeouts set on Google Calendar API calls (3 seconds) - ✅ Calendar name resolution cached **Measurements:** - Latency P95: ~85ms (simple operations like list-events) - Latency P99: ~420ms (complex operations like batch-list-events) - Meets performance targets (<100ms P95, <500ms P99) ✅ **Opportunity:** Add caching for frequently accessed calendar data ### Production Readiness ⚠️ **Implemented:** - ✅ Structured error logging - ✅ Multi-account support (normal/test modes) - ✅ Environment-based configuration **Missing:** - ⚠️ No `/health` endpoint (stdio transport limitation, acceptable) - ⚠️ No metrics collection (Prometheus format) - ⚠️ No explicit monitoring/alerting setup **Recommendations:** 1. Add health check capability for HTTP transport (future) 2. Implement metrics collection: ```typescript // Track tool usage metrics.toolCalls.inc({ tool: toolName }); metrics.toolDuration.observe({ tool: toolName }, duration); ``` 3. Add structured audit logging for sensitive operations ### Issues & Recommendations #### Critical (Must Fix): 1. **Missing consent workflow** ⚠️ - Implement user consent check before tool execution - Violates MCP security requirements - Reference: `implementation-checklist.md` → "Security" #### Recommended (Should Fix): 2. **Add resources capability** - Implement `resources/list` and `resources/read` - URIs like `calendar://events/today`, `calendar://calendars/{id}` - Improves LLM context access 3. **Add prompts capability** - Useful prompts: "schedule-meeting", "review-conflicts", "summarize-week" - Enhances AI assistant workflows 4. **Implement metrics collection** - Track: tool calls, latencies, error rates - Enable production monitoring #### Nice to Have: 5. **HTTP/SSE transport support** - Current stdio-only limits deployment options - HTTP enables remote deployment, web clients - Reference: `protocol-patterns.md` → "Transport" ### Testing ✅ **Current Coverage:** - ✅ Unit tests with mocked Google Calendar API - ✅ Integration tests with real API calls - ✅ Schema validation tests - ✅ Error handling tests **Coverage:** ~92% (exceeds 90% target) ✅ **Recommendation:** Add protocol compliance test suite to validate JSON-RPC 2.0 format programmatically --- ## Summary **Overall Assessment:** ✅ **COMPLIANT** with minor security gap **Protocol Compliance:** ✅ Excellent - Follows JSON-RPC 2.0 and MCP spec 2025-06-18 - Proper capability advertisement - Correct error handling **Security:** ⚠️ Needs improvement - OAuth implementation solid - **Critical gap:** Missing user consent workflow for tool execution **Performance:** ✅ Good - Meets latency targets - Appropriate optimizations (caching, connection reuse) **Production:** ⚠️ Adequate for stdio deployment - Missing metrics/monitoring (recommended for production scale) **Recommended Actions:** 1. **High Priority:** Implement consent workflow (security requirement) 2. **Medium Priority:** Add resources and prompts capabilities 3. **Medium Priority:** Add metrics collection 4. **Low Priority:** Consider HTTP/SSE transport for expanded deployment options **Compliance Status:** 95% - Excellent foundation with one critical security gap to address