Using a remote MCP server

An MCP server is a JSON-RPC 2.0 API behind a single HTTP endpoint. Talk to it with plain fetch from execute or a step, with the MCP connector attached — the platform injects authentication on matching requests, so never set Authorization headers yourself, and never print or store tokens. A 401 or 403 means the connector needs to be reconnected by the user; tell them so rather than attempting an auth flow yourself.

Request basics

Every request is a POST to the server URL with Content-Type: application/json and Accept: application/json, text/event-stream. The response is either plain JSON or an SSE stream; for SSE, parse each data: line as JSON and take the message whose id matches your request. This helper handles both:

let sessionId: string | undefined;