MCP Transport

kicad-mcp-pro supports local MCP workflows through stdio and Streamable HTTP. The extension uses the transport configured in its MCP profile and validates server-info before calling tools.

Streamable HTTP

Use Streamable HTTP when a client needs a stable local endpoint, session handling, bearer-token authentication, or integration with ChatGPT-style connectors.

pip install kicad-mcp-pro
kicad-mcp-pro --transport streamable-http --host 127.0.0.1 --port 3334

The source lives in KiCad MCP Pro.

The default MCP path is /mcp. Set KICAD_MCP_MOUNT_PATH when a client or reverse proxy requires a different endpoint such as /custom-mcp.

Clients must send each JSON-RPC request, response, or notification as a new HTTP POST request to the configured endpoint. Every Streamable HTTP request must include Accept: application/json, text/event-stream and JSON requests must include Content-Type: application/json.

After initialize, clients must include MCP-Protocol-Version: 2025-11-25 on follow-up requests. Stateful deployments also return MCP-Session-Id from initialize; clients must echo that value on notifications/initialized, tools/list, tools/call, and later requests. Missing stateful session IDs return HTTP 400 with a structured JSON-RPC error, and unknown session IDs return HTTP 404 with a structured JSON-RPC error.

The default local mode is stateless Streamable HTTP. This allows ChatGPT-style connectors to initialize, send notifications/initialized, list tools, and call tools without a session-header injection proxy. Set KICAD_MCP_STATEFUL_HTTP=1 only when the deployment needs server-side HTTP session tracking.

Deprecated HTTP+SSE routes are disabled by default. Set KICAD_MCP_LEGACY_SSE=1 only for old clients that cannot speak Streamable HTTP; the compatibility routes are exposed alongside /mcp as /sse and /messages.

Transport conformance coverage lives in the KiCad MCP Pro repository.

stdio

Use stdio when the MCP client launches the server process directly and keeps it bound to the local client session.

pip install kicad-mcp-pro
kicad-mcp-pro --transport stdio

Compatibility

Protocol and capability expectations are generated in MCP API reference. Runtime support boundaries are tracked in the support matrix.