Free MCP Server Tester
MCP Server Tester connects your browser to a remote Model Context Protocol server over Streamable HTTP, runs initialize, lists tools, resources and prompts, and calls tools through a form built from each input schema. Every JSON-RPC message gets conformance checks: ids, error codes, isError results, result shapes, session headers, SSE replies, and structuredContent and arguments against the tool's schemas. Logs pasted from stdio servers are checked offline too.
- Transport:
- Streamable HTTP, JSON or SSE replies
- Checks:
- JSON-RPC 2.0 and MCP up to 2025-11-25
- Network:
- Only the server you enter, no proxy
- Price:
- Free
- Runs:
- Locally, in your browser
- Uploads:
- None: files never leave your device
- Account:
- Not needed
Quick answers
Why does my server fail with a CORS error?
Requests go straight from your browser to the server, with no proxy in between, so the server must allow this page's origin: answer the OPTIONS preflight, send Access-Control-Allow-Origin and allow the headers the tester sends (Content-Type, Mcp-Session-Id, MCP-Protocol-Version, Authorization). When a request fails, the tester tells you whether the host answered at all.
Is my token sent anywhere else?
No. It goes only to the server address you typed, in the Authorization header, never in the URL. It is not saved unless you tick Remember, and it is masked in the log and in the downloaded log.
Processed on your device: your files are never uploaded. How it works
Network activity in this tab
What this page has requested since you opened the site in this tab. An upload is any request that sends data (POST, PUT, PATCH or a request with a body); visit measurement for Google Analytics or advertising is counted separately.
No uploads: nothing has been sent from this page.
No network requests yet.
To see every request, open your browser's developer tools (Network tab).
How to use the MCP Server Tester
- Enter the address of the server's MCP endpoint and, if it needs them, a bearer token or custom headers.
- Press Connect: the tester runs initialize, sends notifications/initialized and lists the tools, resources and prompts the server declares.
- Pick a tool, fill in the form built from its input schema (or switch to JSON) and press Call tool to see content, structuredContent and isError.
- Open the Log tab for every request and response with its conformance checks, or switch to Check a log to analyse a pasted JSON-RPC log offline.
Credits & open source
Our own code plus open-source libraries. Thank you to the people who make these projects.
- @cfworker/json-schemaJSON Schema validator for drafts 4, 7, 2019-09 and 2020-12, without code generation (no eval). © Jeremy Danyow · MIT
Web platform APIs used: Fetch API, Streams API, URL API, File API, Clipboard API, localStorage, Web Workers.
Full license texts: third-party notices · all credits
Frequently asked questions
Can I test a local stdio server?
Not directly: a web page cannot start programs. Record the JSON-RPC messages your server exchanges, one per line, and paste them in Check a log: the same conformance checks run on them.
What do the conformance checks cover?
jsonrpc "2.0", request ids (never null, matched by the response), error codes, the shape of initialize, list, tools/call, resources/read and prompts/get results, isError results versus protocol errors, structuredContent against the tool's outputSchema and arguments against its inputSchema (with the path and keyword of each error; a value that breaks its format is only reported as information, $dynamicRef is not checked, and a schema check that takes more than 3 seconds is stopped), session headers, JSON or event-stream replies, and 202 Accepted for notifications.
Does it support OAuth?
Not in this version. If your server uses OAuth 2.1, get an access token with another client and paste it as the bearer token.