From a script

For a script, the REST API is simpler. But you can also talk to the MCP server directly, for example to test your key or reproduce what your agent sees.

The handshake

The server is stateless: no initialize, no session header. Every request is a POST to https://mcp.rustine.io with:

• Authorization: Bearer rst_...;
• Content-Type: application/json;
• Accept: application/json, text/event-stream (otherwise 406).

Without an MCP-Protocol-Version header, the answer comes as SSE: an event: message line, then data: {…} with the JSON-RPC answer.

As plain JSON

With the 2026-07-28 revision of the protocol, the answer is plain JSON. Add the MCP-Protocol-Version, Mcp-Method and Mcp-Name headers, and the _meta keys in params:

curl -s https://mcp.rustine.io \
  -H "Authorization: Bearer $RUSTINE_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "MCP-Protocol-Version: 2026-07-28" \
  -H "Mcp-Method: tools/call" \
  -H "Mcp-Name: list_projects" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"list_projects","arguments":{},"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientInfo":{"name":"my-script","version":"1.0.0"},"io.modelcontextprotocol/clientCapabilities":{}}}}'

Answers to know

• 401 invalid_token with a WWW-Authenticate header: missing, revoked or mistyped key.
• 406: Accept lacks text/event-stream or application/json.
• Quota used up or plan without MCP: never a 403. The answer is a tool result with isError: true and readable text, with the link to change plans.
• Rate: 120 requests per minute per key, like the API.

Each tool’s parameters: The tools.