MCPJam is the open-source testing & evaluations platform for MCP server developers who ship. Interactively test tools, prompts, resources, and authorization across 16 client configurations and 170+ models. Run evals on test cases, get insights on what's breaking, and gate regressions to secure every deployment.
๐ Quick start
Open the hosted app. No install needed.
๐ app.mcpjam.com
... or run MCPJam locally for HTTP/S and local STDIO servers:
npx @mcpjam/inspector@latest
๐๐ฝ Why MCPJam
Clients like ChatGPT, Claude, and Cursor all read your server differently. MCPJam catches those differences, shows where your server breaks, and tells you how to fix it:
- Inspect & debug: Explore your server's tools, resources, and prompts in one place. Test prompts from real LLMs, with full visibility & traces on every JSON-RPC message and OAuth exchange.
- Cross-client evals: Score agent behavior across 16 client configurations โ ChatGPT, Claude, Cursor, Copilot, and more โ to understand how your MCP integrations perform across all users. Track accuracy, latency, and tool-call performance over time.
- Security & reliability: Automate conformance & behavior checks in CI/CD to catch regressions before they reach production.
Trace view: every tool call, agent step, and JSON-RPC message in one timeline.
</div>๐จ Features
| Capability | What it does |
|---|---|
| Playground | Cross-client chat interface that emulates UIs, tool calls, and skills (with full traces). OpenAI Apps SDK and MCP app UIs, text tools, and a Chrome DevTools-style widget emulator. Read more |
| OAuth Debugger | Visualize your OAuth & EMA requests step-by-step to find the source of errors. Guided MCP OAuth conformance checks across protocol versions 03-26, 06-18, 11-25, and 2026-07-28; DCR, client pre-registration, and CIMD. Read more |
| Server Debugging | Manually run tools, resources, templates, prompts, and elicitation flows with full JSON-RPC logs. |
| Skills | Extend models with reusable behaviors in Playground. Local skills are read from your filesystem and never leave your machine; a project can also carry hosted skills, available on accounts where that is enabled. Read more |
| Workspaces | Shared server groups with real-time team sync, so everyone tests the same config. Read more |
| Evals | Test cases with expected tool calls, run across LLMs, with accuracy metrics over time. Read more |
| CLI | Probe servers, run doctor checks, exercise OAuth, and list tools/resources/prompts from your terminal. Read more |
| SDK | Programmatically drive inspections, snapshot capabilities, and assert on tool/resource shapes from your own tests. Read more |
| CI/CD | Run conformance, E2E tests, evals, and OAuth checks on every PR in GitHub Actions or any pipeline. Read more |
Playground
Debug your server against a model using tool calls or in-panel chat, with Chat, Trace, and Raw views. Supports the OpenAI Apps SDK and MCP app UIs, text tools, and a Chrome DevTools-style widget emulator so you can iterate on widgets locally.
- Invoke a tool to render its widget instantly, or drive your server with an LLM.
- Watch all JSON-RPC and
window.openaimessages in the logs. - Switch the emulator between Desktop, Tablet, and Mobile.
- Test locale changes, CSP permissions, light/dark mode, hover & touch, and safe-area insets.
OAuth Debugger
Guided MCP OAuth conformance checks with step-by-step explanations. Test against every version of the OAuth spec (2025-03-26, 2025-06-18, 2025-11-25, and the 2026-07-28 draft), with support for client pre-registration, Dynamic Client Registration (DCR), and Client ID Metadata Documents (CIMD).
<img alt="MCPJam OAuth flow debugger" src="./docs/images/readme-oauth-debugger.png">Server Debugging
Everything you need to test an MCP server by hand: run tools, resources, resource templates, prompts, and elicitation flows with full JSON-RPC observability. Every feature of the original inspector, and more.
<img alt="MCPJam MCP server debugging view" src="./docs/images/readme-server-debugging.png">Skills
Use Skills in Playground to extend models with reusable behaviors. Local skills are read from your filesystem and never leave your machine; a project can also carry hosted skills, available on accounts where that is enabled. Read more
Workspaces
Group servers into shared workspaces with real-time team sync, so everyone on your team tests against the same configuration. Read more
Evals
Define test cases with expected tool calls and run them across multiple LLMs. Track accuracy over time to catch regressions early and improve your server with every iteration. Read more
CLI
Run MCPJam from the terminal for fast local dev loops and CI. Probe servers, run OAuth checks, inspect tools and resources, and execute evals without leaving your shell. Read more
SDK
Programmatic access to MCPJam for custom tooling, scripting, and integrations. Build your own workflows on top of MCPJam's inspection and evaluation primitives. Read more
CI/CD
Wire MCPJam into GitHub Actions, GitLab CI, or any CI system to run conformance, E2E tests, and evals on every PR โ and catch MCP server regressions before they ship. Read more
๐ Install
MCPJam Inspector runs three ways: a hosted web app, a desktop app for Mac and Windows, or via your terminal. The web app is HTTPS-only and has no install. Terminal and Desktop support HTTP/S and local STDIO servers.
Node.js 20+ is only required for the terminal install (
npx). The hosted and desktop apps have no local runtime requirements.
Hosted web app: Open app.mcpjam.com. No install, always latest, and you can share server links with teammates like a Google Doc. HTTPS server URLs only; no STDIO, tunneling, skills, or tasks (those need the local inspector). Hosted docs
Desktop app: Download the installer. Supports HTTP/S and local STDIO, no Node.js required. Install Mac ยท Install Windows
Terminal: Supports HTTP/S and local STDIO. Open the printed localhost URL after it starts.
npx @mcpjam/inspector@latest
The launcher opens a private access link automatically. To sign in from another browser, use the link printed in your terminal. Docker users can retrieve it with docker logs <container>. Keep it private; a new link is generated on restart unless MCPJAM_SESSION_TOKEN is configured. See the network access instructions for remote addresses and remapped ports.
Docker: Bound to localhost for security. Available at http://127.0.0.1:6274. Always use -p 127.0.0.1:6274:6274 (not -p 6274:6274) to keep the inspector local-only. On macOS/Windows, reach host MCP servers via http://host.docker.internal:PORT.
docker pull mcpjam/mcp-inspector
docker run -p 127.0.0.1:6274:6274 mcpjam/mcp-inspector
๐จโ๐ป Contributing
We're grateful you're considering it. Read the contributing guide to get started, and come say hi in Discord.
๐ Community & links
Website ยท Blog ยท Pricing ยท Docs ยท Discord ยท ๐ (Twitter) ยท LinkedIn ยท YouTube ยท Instagram ยท TikTok
๐ License
Licensed under the Apache License 2.0. See LICENSE.