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modelcontextprotocol/inspector

A visual and command-line developer tool for testing and debugging Model Context Protocol (MCP) servers, with web, CLI, and terminal UI modes.

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What is it?

MCP Inspector lets developers connect to Model Context Protocol servers and inspect what they expose, such as tools, resources, and prompts, and call them directly to check their behavior. It ships as a single package, @modelcontextprotocol/inspector, which exposes one mcp-inspector binary with a web UI (the default), a scriptable CLI, and an interactive terminal UI.

The web UI is a Vite and React single-page app with a Node backend, built with Mantine. The CLI is designed for automation and CI, so a server can be smoke-tested by connecting, listing, calling, and asserting on results, with JSON output usable alongside tools like jq. The TUI uses Ink for an interactive terminal experience.

The package also includes an experimental mcpdo binary, a connection CLI that connects once to a named server and runs many commands through a local daemon. Secrets such as OAuth tokens and stdio environment values are stored in the OS keychain when available, with a file-based fallback.

Key features

  • 01Web UI for browsing and invoking MCP server tools, resources, and prompts
  • 02Scriptable CLI for automation, CI, and smoke tests with JSON output
  • 03Interactive terminal UI built with Ink
  • 04Stores OAuth tokens and secrets in the OS keychain when available
  • 05Experimental mcpdo connection CLI that reuses one connection across commands

Use cases

  • Debugging a custom MCP server during development before connecting it to an AI client
  • Running connect, list, call, and assert checks against an MCP server in CI
  • Testing OAuth-protected MCP servers interactively or non-interactively
  • Exploring an unfamiliar MCP server's available tools and their inputs

Quick start

  1. 1

    Run the web UI with npx (no install needed)

    npx @modelcontextprotocol/inspector
  2. 2

    Or run the command-line client instead

    npx @modelcontextprotocol/inspector --cli

Things to know

  • The license is reported as NOASSERTION, and the README describes a mixed MIT and Apache-2.0 licensing transition, so check LICENSE before reuse.
  • On machines without an OS keychain, secrets such as OAuth tokens are saved unencrypted to ~/.mcp-inspector/secrets.json unless you supply a key.
  • Development requires Node 22.19.0 or newer.

Topics

#mcp#model-context-protocol#debugging#testing#cli#typescript#developer-tools#debug#tool#tui

FAQ

What is inspector?
A visual and command-line developer tool for testing and debugging Model Context Protocol (MCP) servers, with web, CLI, and terminal UI modes. MCP Inspector lets developers connect to Model Context Protocol servers and inspect what they expose, such as tools, resources, and prompts, and call them directly to check their behavior. It ships as a single package, @modelcontextprotocol/inspector, which exposes one mcp-inspector binary with a web UI (the default), a scriptable CLI, and an interactive terminal UI.
Is inspector free to use? What license does it have?
inspector is open source under the Other license. Check the license terms before using it in commercial products.
Is inspector still maintained?
Actively maintained. The last commit to inspector was on Oct 21, 2026.
What can I use inspector for?
Debugging a custom MCP server during development before connecting it to an AI client Running connect, list, call, and assert checks against an MCP server in CI Testing OAuth-protected MCP servers interactively or non-interactively Exploring an unfamiliar MCP server's available tools and their inputs
How do I install inspector?
Run the web UI with npx (no install needed): npx @modelcontextprotocol/inspector Or run the command-line client instead: npx @modelcontextprotocol/inspector --cli
Where can I get inspector?
The source code and installation instructions are on GitHub: https://github.com/modelcontextprotocol/inspector

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