MCP Inspector
A developer tool for inspecting Model Context Protocol (MCP) servers. It ships as a single package, @modelcontextprotocol/inspector, that provides four ways to inspect a server:
- Web — a Vite + React + Mantine single-page app with a Node backend.
- CLI — a scriptable command-line client for automation, CI, and fast agent feedback loops.
- TUI — an interactive terminal UI built with Ink.
- mcpdo (experimental) — a connection CLI: connect once, then run many commands against the named connection through an implicit local daemon. See
clients/mcpdo.
The first three run through one global mcp-inspector binary; mcpdo is a second binary in the same package:
npx @modelcontextprotocol/inspector # web UI (default) npx @modelcontextprotocol/inspector --cli # CLI npx @modelcontextprotocol/inspector --tui # TUI npx -p @modelcontextprotocol/inspector mcpdo --help # mcpdo
Warning
The Inspector manages secrets — OAuth tokens, OAuth client secrets, and stdio env: values — and stores them in the OS keychain, if available, by default. On a machine with no keychain — Linux without libsecret or a Secret Service, headless and SSH sessions, Termux, and containers with a mounted volume — they are saved to ~/.mcp-inspector/secrets.json instead, unencrypted unless you supply a key. See Where secrets are stored for how to get a keychain back, encrypt the file, or keep secrets in memory only.
Upgrading from v1? Read the v1 → v2 migration guide — CLI flags, the new
--configvs.--catalogsplit, the Node engine bump, and what no longer ships.
Repo status. This is the v2 line of the Inspector. Active development happens on
v2/main(the develop branch — all v2 PRs target it), which is merged intomainat milestone releases;mainis the default branch and holds the latest released v2, published to the npmlatesttag. The legacy v1 line lives onv1/main— security fixes only, published straight from that branch to the npmv1-latesttag (npx @modelcontextprotocol/inspector@v1-latest). SeeAGENTS.mdfor branch/board conventions.
Quick start (development)
Requires Node >=22.19.0.
npm install # at the repo root; postinstall cascades into every client npm run build # web → cli → tui → launcher
For day-to-day web iteration, run Vite directly — fast HMR, no launcher build needed:
cd clients/web && npm run dev
The launcher-driven scripts run the built launcher, so build first:
npm run web # prod web launcher against clients/web/dist npm run web:dev # web launcher in --dev mode (Vite)
v2 is not an npm workspace — each client under clients/* keeps its own package.json and node_modules, and shared code lives in core/, consumed via a @inspector/core build-time alias. Every runtime dependency core/ imports is declared once, in the repo-root package.json, and each client declares only what that client alone consumes — its UI stack, its bundler-inlined packages, its dev tooling — which leaves clients/cli and clients/launcher with no runtime dependencies of their own. What that means for adding a dependency (root vs. client, dependencies vs. devDependencies, and the bundler external lists) is in the local-dev skill.
Project layout
inspector/
├── clients/
│ ├── web/ Web client (Vite + React + Mantine). src/ = browser app; server/ = Node backend
│ ├── cli/ CLI client (tsup bundle, @inspector/core alias)
│ ├── mcpdo/ Experimental connection CLI (`mcpdo` bin) — bundled into the
│ │ published package; see clients/mcpdo/README.md
│ ├── tui/ TUI client (Ink + React, tsup bundle)
│ └── launcher/ Shared launcher — provides the `mcp-inspector` bin, dispatches to web/cli/tui
├── core/ Shared code consumed via the `@inspector/core` alias (no package.json)
├── test-servers/ Composable MCP test servers + fixtures used by integration and smoke tests
├── scripts/ Root build/verify tooling (install cascade, smokes, the verify:* guards),
│ repo automation run from CI (the dependency, Dependabot-alert and SDK sweeps),
│ maintainer-workflow helpers (the pr:*, board:*, advisory:*,
│ release:notes, release:tag and action:resolve-pin aliases)
│ and the Docker image's HEALTHCHECK probe
├── docs/ Task-oriented guides — see below
├── specification/ Design/build specifications
├── skills/ End-user agent skills (e.g. skills/mcpdo teaches an agent to
│ drive the `mcpdo` CLI) — distinct from .claude/skills/,
│ which holds this repo's own procedures
├── .claude/skills/ Agent skills: the repo's procedures, invokable by name
├── AGENTS.md Contribution rules for agents AND humans
└── README.md You are here
Each client has its own README with client-specific detail: web · cli · mcpdo · tui · launcher.
Documentation
| Guide | Covers |
|---|---|
| Architecture | The @inspector/core shared package, and the web client's "dumb components" + Storybook approach |
| Testing and the quality gate | What each validate / coverage / smoke / verify:* script covers, the GitHub-CI-vs-local-gate split, and the supported browsers |
| Writing a skill | How to write a skill description that actually fires, and eval cases that measure it — the case shapes that work, and the tuning loop |
| Test servers | The composable test servers and the showcase config for every feature — what to run, what to click, and what the broken build did |
| Publishing | What ships in the tarball, the packaging invariants, and pack:verify |
| Docker | Running the container image — ports, volumes, and making secrets durable in a container |
| Where secrets are stored | How the secret store is chosen on every runtime — OS keychain, secrets.json or memory — plus file encryption, locking, and moving back to a keychain |
| Migrating from v1 to v2 | CLI flag mapping, --config vs. --catalog, the Node engine bump, env-var renames |
| Environment variables | Every variable that changes runtime behavior — auth, ports, storage, the secret store, logging, proxies — plus the Node TLS variables for a self-signed server |
| MCP server configuration | Which server(s) the Inspector connects to, and the config file format |
| Reviewing an MCP App | The CLI-first → one-shot-web recipe for automated App-tool review |
| Smoke-testing an MCP server | The connect → list → call → assert workflow for a shell or CI job: --format json + jq, the exit-code map, and keeping OAuth non-interactive |
| Launcher and config consolidation | Why the launcher runs a client in-process rather than spawning it |
| Roadmap, Aug 2026 → Feb 2027 | The six-month plan: spec-following work aligned to the published MCP roadmap, official extension support, and the experience work we choose |
| MCP Inspector: Our AI Software Factory | How contributions actually happen since v2.0.0 — issue-driven work end to end, the rules/skills split, the sweeps that replaced Dependabot, the quality gate, and where it's headed |
Testing and the quality gate
Each client self-validates from its own folder; the root scripts chain them. There is no aggregate root test script.
npm run validate # fast inner loop: format:check + lint + typecheck + build + unit tests npm run coverage # the per-file ≥90% gate (lines/statements/functions/branches) npm run local:gate # MANDATORY before pushing — every GitHub CI check, plus one local-only one
npm run local:gate chains every check below, plus the smokes and the Storybook tests. Testing and the quality gate owns the stage list and says what each one covers and why one is local-only; AGENTS.md holds the testing rules themselves.
Contributing — AGENTS.md, CLAUDE.md, and the skills
AGENTS.md is the contract for changing this codebase, and it applies to humans and AI agents alike. It is not agent-only boilerplate — it holds the project's real rules: the version/label conventions, the TypeScript and Mantine/React standards, the testing and coverage requirements, and the mandatory pre-push gate. Read it before making changes, and keep it up to date when you change structure, tooling, or rules.
The repo's procedures — multi-step recipes with commands and live IDs — live in .claude/skills/ instead, one directory per procedure, so they are loaded only when the task calls for them. They are ordinary committed Markdown: an agent that doesn't understand skills can read them, and AGENTS.md carries an index of what exists. Claude Code users invoke one by name (/release, /issue-triage, …).
CLAUDE.md is the entry point Claude Code loads automatically; it includes AGENTS.md, so agents and humans work from the same source of truth. If you use a different agent that reads AGENTS.md, you get the same rules.
A key rule worth surfacing here: all work is issue-driven. Before starting, find or create a tracking issue on the v2 project board; open PRs against v2/main with Closes #<issue>. External contributions are accepted as issues, not pull requests — see CONTRIBUTING.md.
License
See LICENSE. The MCP project is transitioning from the MIT License to Apache-2.0: new code contributions are licensed under Apache-2.0, documentation (excluding specifications) under CC-BY-4.0, and contributions whose authors originally licensed them under MIT and have not granted relicensing consent remain under MIT. The file carries the full Apache-2.0 and MIT texts and links the CC-BY-4.0 legal code.