MCP Inspector
by Model Context Protocol
The official visual, CLI and terminal harness for testing and debugging MCP servers.
Overview
MCP Inspector is the Model Context Protocol project's own visual testing harness for MCP servers, distributed as the single npm package @modelcontextprotocol/inspector and exposed through one mcp-inspector binary that fronts three clients: a browser SPA built with Vite, React and Mantine, a scriptable CLI for automation and CI, and a terminal UI built on Ink. Shared connection, request-lifecycle and OAuth logic lives in a core/ directory that all three consume through an @inspector/core build alias, so the same MCP client runtime backs every surface. It requires Node 22.19 or newer and runs without installation via npx, with --cli and --tui flags selecting the other clients, or from the GHCR container image published for linux/amd64 and linux/arm64 on port 6274. Once connected over stdio, SSE or streamable HTTP you can browse the tools, resources and prompts a server advertises, invoke them by hand, and read a live log of every request, response, notification and error. The v2 line supports both the legacy and the 2026-07-28 protocol eras and exercises multi-round tool requests, resource subscriptions, tasks, logging, pagination and advertised extensions, and it ships composable test MCP servers with OAuth presets so you can practise without writing a server first. The repository is MIT-licensed with roughly 10.7k stars and 1.5k forks, and enforces 90% per-file coverage plus Storybook and Playwright checks before merge.
At a Glance
- Topic
- MCP
- Level
- Intermediate
- Format
- Interactive
- Cost
- Free
- Duration
- ~1 hour to learn, then an everyday dev tool
- Provider
- Model Context Protocol
- Hands-on
- Yes — code/exercises
- Certificate
- None
What You’ll Learn
- ✓Inspect the tools, resources and prompts an MCP server advertises
- ✓Invoke tools interactively and read the raw request and response payloads
- ✓Debug live protocol traffic including notifications, logging and error frames
- ✓Choose between the web UI, the CLI and the terminal TUI per workflow
- ✓Exercise stdio, SSE and streamable-HTTP transports against the same server
- ✓Walk OAuth and bearer-token flows before shipping a remote server
- ✓Script inspector runs in CI using --cli mode with JSON config files
- ✓Pin the legacy or 2026-07-28 protocol era to check client compatibility
Highlights
- •First-party tool from the MCP maintainers, MIT-licensed, roughly 10.7k GitHub stars
- •Zero install: npx @modelcontextprotocol/inspector, or a published GHCR Docker image
- •Three clients behind one binary — browser UI, scriptable CLI, and an Ink-based TUI
- •Ships composable test MCP servers with OAuth presets, so you can practise before you have a server
- •A real security lesson is baked into its history: CVE-2025-49596, a CVSS 9.4 remote-code-execution flaw via 0.0.0.0 DNS rebinding against an unauthenticated proxy, affected every version before 0.14.1 (fixed 13 June 2025 with session-token auth, Origin/Host validation and localhost-only binding) — run a current version, and never expose it beyond localhost
Who It’s For
Best For
- ✓Developers building and debugging their first MCP server
- ✓Teams validating server behaviour and OAuth before a public release
- ✓CI engineers automating MCP conformance checks with the CLI
- ✓Client authors comparing legacy and current protocol eras
Prerequisites
- •Node.js 22.19 or newer and basic command-line familiarity
- •A running MCP server to point it at, or use the bundled test servers
- •Working understanding of MCP tools, resources and prompts
FAQ
What is MCP Inspector?
The Model Context Protocol project's own testing tool for MCP servers, shipped as one npm package with three front ends: a browser UI, a scriptable CLI, and a terminal TUI. For anyone building an MCP server who needs to see the tools, resources and prompts it advertises, invoke them by hand, and read the raw protocol traffic before shipping it to a client.
Is MCP Inspector free?
MCP Inspector is free to access.
What level is MCP Inspector for?
MCP Inspector is aimed at a intermediate audience. Recommended background: Node.js 22.19 or newer and basic command-line familiarity, A running MCP server to point it at, or use the bundled test servers, Working understanding of MCP tools, resources and prompts.
How long does MCP Inspector take?
Expect roughly ~1 hour to learn, then an everyday dev tool. Most learners work through it at their own pace.
What will I learn from MCP Inspector?
You'll learn: Inspect the tools, resources and prompts an MCP server advertises; Invoke tools interactively and read the raw request and response payloads; Debug live protocol traffic including notifications, logging and error frames; Choose between the web UI, the CLI and the terminal TUI per workflow; Exercise stdio, SSE and streamable-HTTP transports against the same server; Walk OAuth and bearer-token flows before shipping a remote server; Script inspector runs in CI using --cli mode with JSON config files; Pin the legacy or 2026-07-28 protocol era to check client compatibility.
Topics
Sources
This page was written from 2 sources, 1 on domains other than github.com.