MCP Inspector

The MCP Inspector is an interactive developer tool for testing and debugging MCP servers.

Adapted from MCP Inspector.

Source: modelcontextprotocol/docs (mcp-inspector.png).

Executive summary

Run Inspector via npx against your server command. Use it to verify transport, list resources/prompts/tools, invoke tools with custom inputs, and watch notifications — before wiring a full host.

Getting started

npx @modelcontextprotocol/inspector <command>
npx @modelcontextprotocol/inspector <command> <arg1> <arg2>

npm / PyPI packages

npx -y @modelcontextprotocol/inspector npx @modelcontextprotocol/server-filesystem /Users/username/Desktop

npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git

Local servers

npx @modelcontextprotocol/inspector node path/to/server/index.js args...

npx @modelcontextprotocol/inspector \
  uv \
  --directory path/to/server \
  run \
  package-name \
  args...

Always read the server README for the authoritative launch command.

Feature overview

Area	What you can do
Server connection	Choose transport; customise args and env for local servers
Resources	List, inspect MIME/metadata, read content, test subscriptions
Prompts	List templates, fill arguments, preview messages
Tools	Inspect schemas, call with custom inputs, view results
Notifications	View server logs and protocol notifications

Development workflow

1. Launch Inspector with your server.
2. Verify connectivity and capability negotiation.
3. Change server code → rebuild → reconnect → retest.
4. Probe edge cases: invalid inputs, missing prompt args, concurrent calls, error payloads.

Negative cases

• Wrong working directory → resources/files not found; set --directory / cwd deliberately.
• Missing env vars → tool fails only in Inspector if host injects different env; align both.
• Testing only happy paths → ship brittle servers; add invalid schema tests.

Key takeaways

• Inspector is the MCP equivalent of an API client (Postman-like) for servers.
• Prove tools in Inspector before host integration.
• Include negative tests in every iteration.

What to do next

Return to Debugging or continue with Build an MCP server.