MCP

The gateway serves an MCP endpoint at POST /mcp. Each capability the API key may call appears as a tool with the capability’s name, description, and input schema, so an AI agent works with named business operations instead of database or network access.

Connect a client

For clients that accept the mcpServers format:

{
  "mcpServers": {
    "onprest": {
      "url": "https://gateway.example.com/mcp",
      "headers": {
        "Authorization": "Bearer <YOUR_ONPREST_API_KEY>"
      }
    }
  }
}

If your client asks for a transport, choose Streamable HTTP, not SSE. The endpoint uses stateless JSON-RPC over HTTP and answers with JSON, not an event stream. Supported protocol versions are 2025-03-26, 2025-06-18, and 2025-11-25. Clients negotiate the version during initialize and send it in the MCP-Protocol-Version header afterwards; a request without the header is treated as 2025-03-26.

Browser-based clients must run on an origin listed in GATEWAY_CORS_ALLOWED_ORIGINS.

Methods

Calling a tool

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "get_customer",
    "arguments": { "customer_id": 1 }
  }
}

arguments is the capability’s input object. The tool result contains the same envelope as a REST response, as a text item and, on 2025-06-18 and later, also as structuredContent. On those versions, tools/list includes an outputSchema for each tool.

Files are sent inline in arguments and returned as links or embedded resources; see Files. Annotations set on a capability become the tool hints readOnlyHint, destructiveHint, idempotentHint, and openWorldHint. They describe the tool and do not change what it may do.

Errors

MCP clients see failures at three levels:

A tool error carries the same code and outcome as REST; see Errors. The gateway’s JSON body limit (1 MiB by default) applies to every MCP request.