What Is MCP?
MCP stands for Model Context Protocol. It is an open standard that allows large language models (LLMs) to securely access external data and tools. These resources can include files, databases, search tools, code execution environments, and more.
Conceptually, MCP can be compared to a universal app store for AI applications and assistants, where models interact with external capabilities in a standardized way.
What Is MCP Inspector?
MCP Inspector is an interactive developer tool designed to test and debug MCP servers. When you build an MCP server—whether it exposes data or tools—you need a reliable way to verify that requests, responses, and configurations are working correctly. MCP Inspector fulfills this role.
It provides a web-based interface that allows developers to connect to MCP servers, execute tools, inspect responses, view logs, and troubleshoot issues efficiently.
How MCP Inspector Works
MCP Inspector runs locally and does not require a traditional installation. It is launched using an npx command:
npx @modelcontextprotocol/inspector
What Is npx?
npx is a Node.js package runner. It allows you to execute Node.js packages without installing them globally or locally beforehand. When the command is executed:
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The inspector application is provisioned automatically
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A local web interface is started
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The application becomes available at localhost:6274
Local and Remote MCP Servers
Although MCP Inspector runs locally, it can be used to troubleshoot both:
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Local MCP servers
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Remote MCP servers
A local proxy listens on localhost:6277, handling communication between the inspector UI and the target MCP server. Session tokens are exchanged automatically to establish secure communication.
MCP Inspector User Interface Overview
The MCP Inspector interface consists of two main areas:
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Left panel: Configuration and connection settings
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Main panel: Tool execution, history, and server notifications
Key features include:
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Viewing available tools
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Executing tools with custom input
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Viewing execution history
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Monitoring server notifications and logs
Configuration Options
Transport Types
MCP Inspector supports multiple transport mechanisms:
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Streamable HTTP
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SSE (Server-Sent Events)
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STDIO
You select the appropriate transport based on how your MCP server is implemented.
Connection Methods
You can connect to MCP servers using:
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Direct connection
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Proxy connection
Logging and Debug Levels
Available log levels include:
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Debug
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Info
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Notice
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Warning
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Error
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Critical
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Alert
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Emergency
These options help fine-tune how much diagnostic information is displayed during testing.
Authentication Options
MCP Inspector supports multiple authentication approaches:
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Custom JSON headers
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Authorization headers with secrets
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OAuth 2.0 flow (Client ID, Client Secret, Redirect URL, Scope)
Additional Settings
Other configurable parameters include:
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Request timeout
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Request timeout during progress
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Maximum total timeout
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Proxy address
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Proxy session token
Connecting to an MCP Server
Once configured, connecting to an MCP server initializes the session and retrieves server metadata, including:
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Server name
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Supported capabilities
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Available tools
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Initial log level
After connection, debug options and execution history become available in the interface.
Executing Tools with MCP Inspector
After connecting to a server, MCP Inspector automatically displays the Tools tab.
You can:
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List all available tools
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Select a tool
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Provide the required input (often JSON-based)
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Execute the tool
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Review the response and logs
Example: Community Samples MCP Server
A sample MCP server can expose tools such as:
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Search samples by keyword
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Get samples by product
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Get samples by author
When executing a tool:
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Required parameters must be provided in the expected format
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Some tools require structured JSON input
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Others accept simple text input
For example, searching samples by keyword may return:
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Total result count
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Paginated results
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Detailed metadata for each item
You can control pagination by specifying:
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Page index
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Page size
All executed actions are recorded in the History panel, allowing you to trace every request and configuration change.
Documentation and Resources
To better understand MCP Inspector and MCP architecture, official documentation is available at:
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modelcontextprotocol.io/docs/tools/inspector
The documentation covers:
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MCP architecture (servers and clients)
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Connecting to local and remote MCP servers
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Building MCP servers and MCP clients
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Supported transport mechanisms
Additionally, the GitHub repository:
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modelcontextprotocol/inspector
provides source code and implementation details for the inspector tool.
Conclusion
MCP Inspector is a powerful, developer-friendly tool for validating and debugging MCP servers. With support for multiple transports, authentication mechanisms, detailed logging, and both local and remote connections, it simplifies the development and testing workflow for Model Context Protocol–based systems.
By using MCP Inspector, developers can confidently build, test, and maintain MCP servers that integrate AI models with real-world data and tools.