MCP Inspector

What is MCP Inspector?

The Model Context Protocol, or MCP, is an open standard introduced by Anthropic in late 2024 that lets AI applications connect to external tools and data sources. If you have ever built an MCP server, you know the experience of testing it blindly, and MCP Inspector exists to fix exactly that.

MCP Inspector is the official developer tool for the protocol. It runs as a small local web application that connects to any MCP server and lets you explore what the server exposes: tools, their input schemas, resources and prompts. You can then invoke a tool with your own arguments and read the raw JSON response, which makes debugging much less painful.

It ships as part of the MCP ecosystem and works with both main transport types: stdio for local servers you launch from a command, and HTTP (SSE) for remote servers you connect to over the network.

Key Features

• Tool browser showing every tool a server exposes
• Schema inspector for tool input arguments
• Live test invocation with custom JSON arguments
• Support for both stdio and HTTP (SSE) transports
• Connection configuration for environment variables and command arguments
• Raw request and response viewer for deep debugging
• Also available as a hosted web app for testing remote servers

How to get started

The quickest way to launch the Inspector is with npx, the Node.js package runner. Run npx @modelcontextprotocol/inspector and it starts a local web app, usually on port 6274, and opens it in your browser.

From there you choose your transport. For a local server, provide the command that starts it, for example npx or python with the server entry point. For a remote server, paste the server URL. Once connected, you can browse tools and start testing calls immediately.

• Make sure Node.js is installed
• Run npx @modelcontextprotocol/inspector
• Open the local web app in your browser
• Pick stdio and enter the server command, or pick HTTP and enter the server URL
• Browse tools, inspect schemas and invoke test calls

Use cases

• Developing and debugging new MCP servers
• Finding out why a tool call fails or returns unexpected data
• Validating that tool schemas look right for AI clients
• Testing remote MCP servers before putting them into production
• Learning how MCP works by exploring a real server
• Comparing how different tools respond to the same arguments

Pricing and licensing

MCP Inspector is free and open source under the MIT license, like the rest of the official MCP tooling. There are no paid tiers, no accounts and no usage limits; you run it locally and it stays on your machine.

Because the project is maintained by the MCP team, it tends to stay in sync with the protocol specification, which is a nice guarantee when the standard is still evolving quickly.

Pros and cons

The biggest advantages are that it is official, free and zero-configuration for local servers. Being part of the MCP project means it tracks the spec closely, and the schema view is genuinely useful for spotting mismatches between what a server advertises and what it actually accepts.

On the downside, it is a developer utility rather than a full test runner, so it will not write your integration tests for you. Some parts of the interface still feel rough around the edges, and it requires Node.js even if your server itself is written in another language.

Alternatives

• Raw MCP client scripts written with the official SDKs
• MCP-enabled AI tools such as Claude Code with built-in server management
• Postman or similar API clients for testing HTTP-based MCP servers
• Community MCP test runners and schema validators