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.
🚀 Quick start
Open the hosted app. No install needed.
👉 app.mcpjam.com
... or run MCPJam locally for HTTP/S and local STDIO servers:
npx @mcpjam/inspector@latest
👋🏽 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 — ChatGPT, Claude, Cursor, Copilot, and more — 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.
🔨 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.openai messages 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).
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.
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
This is the beginning of the README. Read the rest at the original. Read the full README ↗
