# MCPJam Inspector - Local Development and Testing Tool for MCP Servers > MCPJam Inspector is a comprehensive local development and testing tool for MCP servers, ChatGPT apps, and MCP Apps (ext-apps/SEP-1865). It provides a full widget emulator for ChatGPT and Claude app... - Skill: `tools-only/mcpjam-inspector-local-development-and-testing-tool-for-mcp-` (Agent Skill, multi-file: 3 files) - Install (CLI): `npx skillmds@latest add tools-only/mcpjam-inspector-local-development-and-testing-tool-for-mcp-` - Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/mcpjam-inspector-local-development-and-testing-tool-for-mcp-/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - License: Apache-2.0 - Author: tools-only (https://skillmd.com/u/tools-only) - Updated: 2026-09-09 - Page: https://skillmd.com/skills/tools-only/mcpjam-inspector-local-development-and-testing-tool-for-mcp- --- ## Overview MCPJam Inspector is a comprehensive local development and testing tool for MCP servers, ChatGPT apps, and MCP Apps (ext-apps/SEP-1865). It provides a full widget emulator for ChatGPT and Claude app development, an LLM playground with free access to frontier models (GPT-5, Claude Sonnet), OAuth debugging, test case management with AI generation, and E2E evaluation capabilities via CLI. **Core Value Proposition**: Eliminates the need for ngrok or ChatGPT subscriptions during MCP server and app development by providing a complete local testing environment with multi-LLM support. --- ## Problem Addressed | Problem | How MCPJam Solves It | | ----------------------------------------------------- | ---------------------------------------------------------------- | | Complex MCP server setup for local testing | Single npx command starts full inspector with web UI | | ChatGPT app development requires ngrok + subscription | Full widget emulator runs locally with no external dependencies | | MCP Apps (Claude ext-apps) lack development tooling | Complete SEP-1865 support with all JSON-RPC message types | | OAuth 2.1 implementation debugging is complex | Visual step-by-step OAuth debugger with multi-protocol support | | Testing MCP tools across different LLMs is expensive | Free access to GPT-5 and Claude Sonnet in playground | | Manual test case creation is time-consuming | AI-powered test generation from tool definitions | | E2E testing MCP servers across clients is fragmented | CLI-based eval framework simulates different client environments | --- ## Key Statistics (as of January 26, 2026) | Metric | Value | | ---------------- | --------------------- | | GitHub Stars | 1,598 | | Forks | 177 | | Open Issues | 14 | | Primary Language | TypeScript | | npm Package | @mcpjam/inspector | | CLI Package | @mcpjam/cli | | Latest Version | v1.5.0 (Jan 20, 2026) | | Created | May 23, 2025 | | Last Updated | Jan 25, 2026 | --- ## Key Features ### 1. MCP Server Inspection - **Multi-Server Connection**: Connect to multiple MCP servers simultaneously - **Tool Testing**: Manually invoke tools with custom parameters, view JSON-RPC logs - **Resource & Prompt Testing**: Test resources, resource templates, and prompts - **Server Information**: View icons, versions, capabilities, and instructions - **All JSON-RPC Logging**: Real-time protocol message inspection ### 2. ChatGPT Apps SDK Support - **Full `window.openai` API**: Complete support for `widgetState`, `callTool`, `structuredContent`, `sendFollowUpMessage`, `displayMode` - **Widget Emulator**: Preview widgets without ChatGPT subscription - **Device Emulation**: Test across Desktop, Tablet, Mobile viewports - **CSP Testing**: Validate Content Security Policy configurations - **Theme/Locale Testing**: Light/dark modes, internationalization testing - **Safe Area Insets**: Simulate device notches and gesture areas ### 3. MCP Apps (SEP-1865) Support - **Full JSON-RPC Message Types**: `tools/call`, `ui/initialize`, `ui/message`, `ui/open-link` - **Inline Widget Rendering**: Render `ui.resourceUri` components in chat - **Display Modes**: Inline, Picture-in-Picture, Fullscreen support ### 4. OAuth Debugger - **Visual Step-by-Step**: Interactive OAuth handshake walkthrough - **Multi-Protocol Versions**: Supports specs 03-26, 06-18, and 11-25 - **Registration Methods**: Client pre-registration, DCR, and CIMD - **Network Inspection**: View all HTTP requests/responses with headers - **Sequence Diagrams**: Visual flow synchronized with progress ### 5. LLM Playground - **Free Frontier Models**: GPT-5, Claude Sonnet, Gemini 2.5 at no cost - **Multi-Provider Support**: OpenAI, Anthropic, Google, Deepseek, Mistral, Ollama, OpenRouter, LiteLLM - **Split-Panel Interface**: Chat on left, JSON-RPC logs on right - **MCP Prompts**: Use prompts directly via `/` command - **Elicitation Support**: Handle interactive prompts from MCP servers - **Customizable Agent**: System prompts, temperature settings ### 6. Test Cases - **AI-Powered Generation**: Auto-generate tests from tool definitions using Claude Haiku - **Positive/Negative Tests**: Test both tool triggering and non-triggering scenarios - **Multi-Model Evaluation**: Run tests across different LLM providers - **Accuracy Metrics**: Track pass rates, token consumption, duration - **Run History**: Compare performance across runs and models - **App Store Compliance**: Generate required test cases for ChatGPT app submission ### 7. MCP Evals (CLI) - **E2E Testing**: Simulate end-user environments - **Environment Simulation**: Test as Claude Desktop, Cursor, etc. - **Multiple Servers**: Test against multiple MCP servers - **CI/CD Integration**: JSON-based configuration for automation --- ## Technical Architecture MCPJam Inspector | +--------------------+--------------------+ | | | Web UI CLI Tool Desktop App (localhost:6274) (@mcpjam/cli) (Mac/Windows) | | | +--------------------+--------------------+ | +-------------+-------------+ | | | MCP Servers ChatGPT Apps MCP Apps (stdio/HTTP) (window.openai) (SEP-1865) | | | +-------------+-------------+ | +------+----+----+------+ | | | | | OpenAI Claude Gemini Ollama ... (GPT-5) (Sonnet) (Local) ### Deployment Options **npx (Quick Start)**: ```bash npx @mcpjam/inspector@latest ``` **Docker**: ```bash docker run -p 127.0.0.1:6274:6274 mcpjam/mcp-inspector ``` **Desktop App**: Native Mac (.dmg) and Windows (.exe) installers available **With MCP Server**: ```bash npx @mcpjam/inspector@latest npx -y @modelcontextprotocol/server-everything ``` ### Configuration Supports Claude Desktop-style configuration files: ```json { "mcpServers": { "weather-server": { "command": "python", "args": ["weather_server.py"], "env": { "WEATHER_API_KEY": "${WEATHER_API_KEY}" } } } } ``` Launch with: `npx @mcpjam/inspector@latest --config path/to/config.json` --- ## Installation and Usage ### Quick Start ```bash # Start inspector npx @mcpjam/inspector@latest # Open browser to http://localhost:6274 ``` ### Start with MCP Server ```bash # Python FastMCP server npx @mcpjam/inspector@latest uv run fastmcp run /path/to/server.py # Node.js server npx @mcpjam/inspector@latest npx -y your-mcp-package ``` ### Start with Ollama ```bash npx @mcpjam/inspector@latest --ollama llama3.2 ``` ### MCP Evals CLI ```bash # Install CLI globally npm install -g @mcpjam/cli # Run evaluations mcpjam evals run --tests tests.json --environment env.json ``` ### Test File Format ```json { "tests": [ { "title": "Test weather tool", "query": "What's the weather in San Francisco?", "expectedTools": ["get_weather"], "model": { "id": "claude-3-5-sonnet-20241022", "provider": "anthropic" }, "selectedServers": ["weather-server"] } ] } ``` --- ## Comparison with Alternatives | Feature | MCPJam | Official MCP Inspector | Postman | Custom Testing | | -------------------- | ----------------- | ---------------------- | ------- | ------------------ | | MCP Server Testing | Yes | Yes | Partial | Manual | | ChatGPT Apps Support | Yes | No | No | Manual | | MCP Apps (SEP-1865) | Yes | No | No | Manual | | OAuth Debugger | Yes (visual) | Basic | Yes | Manual | | LLM Playground | Yes (free models) | No | No | Requires API keys | | AI Test Generation | Yes | No | No | No | | E2E Evals CLI | Yes | No | No | Manual | | Widget Emulator | Full | No | No | Manual | | Multi-Provider LLMs | 8+ providers | N/A | N/A | Per-provider setup | --- ## Relevance to Claude Code Development ### Direct Applications 1. **MCP Server Development**: Test custom MCP servers before integrating with Claude Code 2. **OAuth Flow Debugging**: Debug authentication for MCP servers requiring OAuth 3. **Tool Testing**: Manually invoke and verify tool behavior before deployment 4. **Multi-LLM Validation**: Verify MCP servers work across Claude, GPT, Gemini models ### Patterns Worth Adopting 1. **Visual OAuth Debugging**: Step-by-step handshake visualization pattern 2. **AI Test Generation**: Using LLMs to generate test cases from tool definitions 3. **E2E Eval Framework**: JSON-based test configuration for CI/CD integration 4. **Free Frontier Model Access**: Proxied access pattern for development tools 5. **Widget Emulation**: Iframe isolation with injected APIs for UI testing 6. **Multi-Protocol Support**: Backwards-compatible OAuth spec handling ### Integration Opportunities 1. **Claude Code Plugin**: Create plugin that launches MCPJam for connected MCP servers 2. **Pre-Deployment Testing**: Integrate MCPJam evals into plugin CI/CD pipelines 3. **OAuth Debugging Workflow**: Use MCPJam for debugging MCP OAuth implementations 4. **Test Case Library**: Generate and maintain test cases for Claude Code MCP integrations ### Complementary to Existing MCP Ecosystem Research MCPJam fills a testing and development tooling gap: - **Narsil MCP**: Code intelligence and security scanning (runtime) - **OctoCode MCP**: Research Driven Development with GitHub search (research) - **Docs MCP Server**: Documentation grounding and retrieval (knowledge) - **MCPJam**: Development, testing, and evaluation (DevOps/QA) --- ## References 1. **Documentation**: (accessed 2026-01-26) 2. **GitHub Repository**: (accessed 2026-01-26) 3. **npm Package (@mcpjam/inspector)**: (accessed 2026-01-26) 4. **npm Package (@mcpjam/cli)**: (accessed 2026-01-26) 5. **Getting Started Guide**: (accessed 2026-01-26) 6. **OAuth Debugger**: (accessed 2026-01-26) 7. **App Builder**: (accessed 2026-01-26) 8. **LLM Playground**: (accessed 2026-01-26) 9. **Test Cases**: (accessed 2026-01-26) 10. **MCP Evals**: (accessed 2026-01-26) 11. **MCP Protocol Specification**: (accessed 2026-01-26) 12. **ChatGPT Apps SDK**: (accessed 2026-01-26) 13. **MCP Apps SEP-1865**: (accessed 2026-01-26)