Website Reputation Checker

The MCP inspector is a developer tool for testing and debugging MCP servers.

The MCP Inspector consists of two main components that work together:

- MCP Inspector Client (MCPI): A React-based web UI that provides an interactive interface for testing and debugging MCP servers
- MCP Proxy (MCPP): A Node.js server that acts as a protocol bridge, connecting the web UI to MCP servers via various transport methods (stdio, SSE, streamable-http)

Note that the proxy is not a network proxy for intercepting traffic. Instead, it functions as both an MCP client (connecting to your MCP server) and an HTTP server (serving the web UI), enabling browser-based interaction with MCP servers that use different transport protocols.

To get up and running right away with the UI, just execute the following:

The server will start up and the UI will be accessible athttp://localhost:6274.

To inspect an MCP server implementation, there's no need to clone this repo. Instead, usenpx. For example, if your server is built atbuild/index.js:

npx @modelcontextprotocol/inspector node build/index.js

You can pass both arguments and environment variables to your MCP server. Arguments are passed directly to your server, while environment variables can be set using the-eflag:

# Pass arguments only npx @modelcontextprotocol/inspector node build/index.js arg1 arg2 # Pass environment variables only npx @modelcontextprotocol/inspector -e key=value -e key2=$VALUE2 node build/index.js # Pass both environment variables and arguments npx @modelcontextprotocol/inspector -e key=value -e key2=$VALUE2 node build/index.js arg1 arg2 # Use -- to separate inspector flags from server arguments npx @modelcontextprotocol/inspector -e key=$VALUE -- node build/index.js -e server-flag

The inspector runs both an MCP Inspector (MCPI) client UI (default port 6274) and an MCP Proxy (MCPP) server (default port 6277). Open the MCPI client UI in your browser to use the inspector. (These ports are derived from the T9 dialpad mapping of MCPI and MCPP respectively, as a mnemonic). You can customize the ports if needed:

CLIENT_PORT=8080 SERVER_PORT=9000 npx @modelcontextprotocol/inspector node build/index.js

For more details on ways to use the inspector, see theInspector section of the MCP docs site. For help with debugging, see theDebugging guide.

{ "command": "node", "args": ["build/index.js", "--debug"], "env": { "API_KEY": "your-api-key", "DEBUG": "true" } }

{ "type": "sse", "url": "http://localhost:3000/events", "note": "For SSE connections, add this URL directly in Client" }

Servers File- Copies a complete MCP configuration file structure to your clipboard, with your current server configuration added asdefault-server. This can be saved directly asmcp.json.

{ "mcpServers": { "default-server": { "command": "node", "args": ["build/index.js", "--debug"], "env": { "API_KEY": "your-api-key", "DEBUG": "true" } } } }

{ "mcpServers": { "default-server": { "type": "sse", "url": "http://localhost:3000/events", "note": "For SSE connections, add this URL directly in Client" } } }

These buttons appear in the Inspector UI after you've configured your server settings, making it easy to save and reuse your configurations.

For SSE transport connections, the Inspector provides similar functionality for both buttons. The "Server Entry" button copies the SSE URL configuration that can be added to your existing configuration file, while the "Servers File" button creates a complete configuration file containing the SSE URL for direct use in clients.

You can paste the Server Entry into your existingmcp.jsonfile under your chosen server name, or use the complete Servers File payload to create a new configuration file.

The inspector supports bearer token authentication for SSE connections. Enter your token in the UI when connecting to an MCP server, and it will be sent in the Authorization header. You can override the header name using the input field in the sidebar.

The MCP Inspector includes a proxy server that can run and communicate with local MCP processes. The proxy server should not be exposed to untrusted networks as it has permissions to spawn local processes and can connect to any specified MCP server.

The MCP Inspector proxy server requires authentication by default. When starting the server, a random session token is generated and printed to the console:

🔑 Session token: 3a1c267fad21f7150b7d624c160b7f09b0b8c4f623c7107bbf13378f051538d4 🔗 Open inspector with token pre-filled: http://localhost:6274/?MCP_PROXY_AUTH_TOKEN=3a1c267fad21f7150b7d624c160b7f09b0b8c4f623c7107bbf13378f051538d4

This token must be included as a Bearer token in the Authorization header for all requests to the server. The inspector will automatically open your browser with the token pre-filled in the URL.

Automatic browser opening- The inspector now automatically opens your browser with the token pre-filled in the URL when authentication is enabled.

Alternative: Manual configuration- If you already have the inspector open:
- Click the "Configuration" button in the sidebar
- Find "Proxy Session Token" and enter the token displayed in the proxy console
- Click "Save" to apply the configuration

The token will be saved in your browser's local storage for future use.

If you need to disable authentication (NOT RECOMMENDED), you can set theDANGEROUSLY_OMIT_AUTHenvironment variable:

By default, both the MCP Inspector proxy server and client bind only tolocalhostto prevent network access. This ensures they are not accessible from other devices on the network. If you need to bind to all interfaces for development purposes, you can override this with theHOSTenvironment variable:

Warning:Only bind to all interfaces in trusted network environments, as this exposes the proxy server's ability to execute local processes and both services to network access.

To prevent DNS rebinding attacks, the MCP Inspector validates theOriginheader on incoming requests. By default, only requests from the client origin are allowed (respectsCLIENT_PORTif set, defaulting to port 6274). You can configure additional allowed origins by setting theALLOWED_ORIGINSenvironment variable (comma-separated list):

ALLOWED_ORIGINS=http://localhost:6274,http://localhost:8000 npm start

The MCP Inspector supports the following configuration settings. To change them, click on theConfigurationbutton in the MCP Inspector UI:

These settings can be adjusted in real-time through the UI and will persist across sessions.

The inspector also supports configuration files to store settings for different MCP servers. This is useful when working with multiple servers or complex configurations:

npx @modelcontextprotocol/inspector --config path/to/config.json --server everything

{ "mcpServers": { "everything": { "command": "npx", "args": ["@modelcontextprotocol/server-everything"], "env": { "hello": "Hello MCP!" } }, "my-server": { "command": "node", "args": ["build/index.js", "arg1", "arg2"], "env": { "key": "value", "key2": "value2" } } } }

Tip:You can easily generate this configuration format using theServer EntryandServers Filebuttons in the Inspector UI, as described in the Servers File Export section above.

You can also set the initialtransporttype,serverUrl,serverCommand, andserverArgsvia query params, for example:

http://localhost:6274/?transport=sse&serverUrl=http://localhost:8787/sse http://localhost:6274/?transport=streamable-http&serverUrl=http://localhost:8787/mcp http://localhost:6274/?transport=stdio&serverCommand=npx&serverArgs=arg1%20arg2

You can also set initial config settings via query params, for example:

http://localhost:6274/?MCP_SERVER_REQUEST_TIMEOUT=10000&MCP_REQUEST_TIMEOUT_RESET_ON_PROGRESS=false&MCP_PROXY_FULL_ADDRESS=http://10.1.1.22:5577

Note that if both the query param and the corresponding localStorage item are set, the query param will take precedence.

If you're working on the inspector itself:

Note for Windows users:On Windows, use the following command instead:

CLI mode enables programmatic interaction with MCP servers from the command line, ideal for scripting, automation, and integration with coding assistants. This creates an efficient feedback loop for MCP server development.

npx @modelcontextprotocol/inspector --cli node build/index.js

The CLI mode supports most operations across tools, resources, and prompts. A few examples:

# Basic usage npx @modelcontextprotocol/inspector --cli node build/index.js # With config file npx @modelcontextprotocol/inspector --cli --config path/to/config.json --server myserver # List available tools npx @modelcontextprotocol/inspector --cli node build/index.js --method tools/list # Call a specific tool npx @modelcontextprotocol/inspector --cli node build/index.js --method tools/call --tool-name mytool --tool-arg key=value --tool-arg another=value2 # List available resources npx @modelcontextprotocol/inspector --cli node build/index.js --method resources/list # List available prompts npx @modelcontextprotocol/inspector --cli node build/index.js --method prompts/list # Connect to a remote MCP server (default is SSE transport) npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com # Connect to a remote MCP server (with Streamable HTTP transport) npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com --transport http # Call a tool on a remote server npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com --method tools/call --tool-name remotetool --tool-arg param=value # List resources from a remote server npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com --method resources/list

This project is licensed under the MIT License—see theLICENSEfile for details.

Bring agent evaluations, observability, and synthetic test set generation directly into your IDE for free with Galileo's new MCP server