MCP Playground
The MCP Playground is a visual interface for inspecting, testing, and debugging MCP servers. It allows developers to simulate requests, inspect tool schemas, and validate execution results — all without writing client code.
This guides walks through:
- What the Playground is and why it's useful
- Core features like tool inspection and manual testing
- Common workflows (e.g., testing STDIO vs. SSE)
- How to troubleshoot errors before production deployment
Introduction
The Playground is a developer tool that connects directly to your MCP server and gives you a live interface to:
| Feature | Description |
|---|---|
| Connect to a server | Choose STDIO or SSE, provide the server path or URL |
| List tools | Automatically fetch tool schema from capabilities.json |
| Test tool calls | Manually input parameters and run the tool |
| View responses | See formatted output, errors, or return values |
| Track tool history | Review previous executions in a live session |
It's your "debug console" for validating server behavior before clients call it. You can also access it via modelcontextprotocol.io/inspector (opens in a new tab).
Debugging
The Playground saves hours by letting you: Debug tool behaviors quickly; Share visual results with your team; Confirm server compatibility before public release.
Depending on the connection type, the Playground works slightly differently:
| Connection | Setup Needed | Notes |
|---|---|---|
| STDIO | Local path to .js or .py file | Server is launched in background |
| SSE | URL to a cloud endpoint (e.g., Vercel API route) | Must support streaming and return valid tool list |
Once connected, the Playground:
- Sends a
list_toolsrequest - Shows available tools with their input schema
- Lets you fill in test values and submit a request
Use Case
To verify the MCP server:
- Click Playground from the header menu.
-
In the MCP Inspector section:
- Choose the MCP Server type:
STDIOorSSE - Enter the service URL and click Connect
- If successful, the status will turn green and show Connected
- Choose the MCP Server type:
-
Under the Tools section, click List Tools to view all available tools defined in your API.
- Select and run individual tools by clicking Run Tool
- Input the required parameters.
- View the execution response in the History section.