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kitty/binAI
Straight from your browser to your server

Test an MCP server without installing anything

Connect to a Model Context Protocol server over Streamable HTTP or SSE. See its tools, resources and prompts, call any tool from a form built from its input schema, and read every JSON-RPC message that goes back and forth.

Transport

Requests go directly from your browser to the address above; kittybin’s servers never see them. The token is held in memory for this tab only and is never saved. The server must allow requests from web pages (CORS); if it doesn’t, you’ll see exactly what to change.

Not connected

JSON-RPC traffic

Messages appear here once you connect.

Streamable HTTP or SSE?

Streamable HTTP is the current MCP transport: every message is a POST to one address, often ending in /mcp, and the server answers with JSON or a short event stream. SSE is the older transport: the client keeps a stream open, usually at /sse, and the server tells it where to post messages. If one doesn’t connect, try the other.

Making your server work from a browser

Browsers only let a page talk to another site if that site agrees. Your server needs to answer OPTIONS requests and send Access-Control-Allow-Origin with this site’s address (or *), Access-Control-Allow-Headers: content-type, authorization, mcp-session-id, mcp-protocol-version, and Access-Control-Expose-Headers: mcp-session-id so the session ID can be read. Local servers on localhost work too, as long as they allow this origin.

What happens when you connect

The tester sends initialize with protocol version 2025-06-18, sends the initialized notification, then asks for tools/list, resources/list and prompts/list for whatever the server says it supports. Calling a tool sends tools/call with the arguments from the form. Every request and reply is shown in the traffic log exactly as sent and received.

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