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MCPJam Inspector

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Open-source testing and evaluations platform for MCP server developers

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★ 2.2k Stars Category · Dev Tools Very popular Source revision bf783630567a

58FMRS · C

Reliability

8/20

Security and permissions

13/20

Maintenance

11/20

Documentation

13/20

Setup experience

13/20

MCPJam Inspector is a mature open-source MCP testing and debugging platform covering tool invocation, OAuth flows, cross-client evals, and CI/CD integration; the README is well documented with multiple deployment options, making it a solid debugging and quality-assurance tool for MCP server developers.

Read the FMRS scoring method →

MCPJam Inspector is an open-source testing and evaluations platform for interactively inspecting and debugging MCP (Model Context Protocol) servers, MCP apps, and ChatGPT apps. It is not itself an MCP server exposing tools — it is an MCP client/debugging tool that connects to local (STDIO) or remote (HTTP/S) MCP servers, letting developers manually run tools, resources, resource templates, prompts, and elicitation flows while viewing full JSON-RPC logs. It supports cross-client evals across 16 client configurations (ChatGPT, Claude, Cursor, Copilot, and more) and 170+ models, includes a guided OAuth debugger covering multiple protocol versions (2025-03-26, 2025-06-18, 2025-11-25, and the 2026-07-28 draft, with DCR, client pre-registration, and CIMD support), a traced Playground chat interface with a Chrome DevTools-style widget emulator for OpenAI Apps SDK and MCP app UIs, Skills, team Workspaces, test-case Evals, and a CLI/SDK for CI/CD pipelines. It can be used via the hosted web app (app.mcpjam.com), a Mac/Windows desktop app, or run locally via npx @mcpjam/inspector@latest; a Docker image can also be built from source.

Tools

The tool list has not been reviewed yet.

Setup

Choose the installation method that fits your use case: 1) Hosted web app — open app.mcpjam.com, no install required, HTTPS server URLs only, no STDIO, tunneling, skills, or tasks; 2) Desktop app — download the Mac (.dmg) or Windows (.exe) installer from GitHub Releases, supports HTTP/S and local STDIO servers, no Node.js required; 3) Terminal — requires Node.js 20+, run npx @mcpjam/inspector@latest and open the printed localhost URL, supports HTTP/S and local STDIO; 4) Docker — no published image exists, so clone the repo and build from the included Dockerfile (docker build -t mcpjam/mcp-inspector:local -f mcpjam-inspector/Dockerfile .), always run with -p 127.0.0.1:6274:6274 (not -p 6274:6274) to keep it local-only, and on macOS/Windows reach host MCP servers via http://host.docker.internal:PORT.

Fit and risk

Best for

Developers building or maintaining MCP servers who need to verify consistent behavior across many clients
Teams wanting to add MCP conformance and regression testing to their CI/CD pipeline
Developers debugging OAuth/DCR/CIMD authorization flows
Developers previewing and iterating on Apps SDK / MCP app widget UIs locally

Not for

End users who just want to plug an MCP server into an assistant client (this is a developer debugging tool, not an end-user MCP server)
Users needing hosted-only features like skill sync or tasks in a fully offline environment, since the hosted app is HTTPS-only and some features are local-only
Users looking for an MCP server implementation that exposes tools to an AI assistant

Required permissions

Network access to connect to target MCP servers (local STDIO process or remote HTTP/S endpoint)
The local/desktop build launches and communicates with local STDIO subprocesses, i.e. it can execute local commands
The OAuth debugger accesses and handles authorization credentials and token exchanges
A self-built Docker image binds to a local port (127.0.0.1 by default) requiring local port access

Risks and side effects

As a debugging tool it logs and displays full JSON-RPC messages and OAuth exchange details, so logs may contain sensitive tokens or credentials
Docker deployments that use `-p 6274:6274` instead of `-p 127.0.0.1:6274:6274` could expose the debugging port publicly
The hosted web app cannot be used for STDIO-only servers since it only supports HTTPS endpoints
The repository's license field is listed as NOASSERTION even though the README states Apache 2.0 — verify actual license terms before relying on this project

Troubleshooting

Confirm the install method supports the transport you need: the hosted app is HTTPS-only, while STDIO servers require the desktop app or terminal `npx` install
The terminal install requires Node.js 20+; an older Node version will cause the npx command to fail
For Docker, verify the port mapping uses `127.0.0.1:6274:6274`, and on macOS/Windows use `host.docker.internal` instead of `localhost` to reach host-run MCP servers
If OAuth debugging errors occur, check which protocol version (2025-03-26, 2025-06-18, 2025-11-25, or the 2026-07-28 draft) the target server implements against the versions the debugger supports
If features like Skills, tasks, or tunneling appear missing, check whether you're using the hosted web app, since those are local/desktop-only features

Use cases

Manually invoking and debugging an MCP server's tools, resources, and prompts with full JSON-RPC visibility during development

Debugging and validating MCP OAuth / EMA authorization flows and tracing errors across protocol versions

Running eval test cases across multiple LLM client configurations and tracking tool-call accuracy over time

Automating conformance, end-to-end tests, and evals in CI/CD to catch regressions before release

Iterating locally on widgets for servers that use the OpenAI Apps SDK or MCP app UIs

Supported clients

Supported clients have not been confirmed yet.

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