MCP & Connectors
What is the MCP server URL format for Claude connectors?
QUICK ANSWER
The Model Context Protocol (MCP) uses Server-Sent Events (SSE) for HTTP transport, where the client establishes a SSE connection to a GET endpoint (e.g. http://localhost:3000/sse) and sends JSON-RPC client-to-server messages via POST requests to a separate endpoint declared by the server.
Format Specification
While local MCP connections run over Standard Input/Output (stdio) using child processes, remote connections utilize Server-Sent Events (SSE). The URL structure requires two components:
- SSE Connection Endpoint: The entry point where the Claude client starts a GET request to open a persistent events connection stream. For example:
http://localhost:3000/sse. - HTTP POST Route: Once connected, the server sends a unique session identifier. The client sends JSON-RPC payload commands to the corresponding post URL, typically structured as:
http://localhost:3000/message?sessionId=<session_id>.
Example Endpoint Configurations
| Transport Mode | Endpoint / Connection Scheme | Authentication Payload Location |
|---|---|---|
| Stdio (Local) | Process Execution (e.g., npx @modelcontextprotocol/server-postgres) |
Environment Variables (e.g., PGPASSWORD) |
| Remote SSE (HTTP) | http://[domain]/sse or https://[domain]/sse |
Authorization Header / Bearer Token |
Verified against: MCP Spec v1.0.4