Secure MCP Tunnel client
The customer-run client for OpenAI's Secure MCP Tunnel, connecting a private or localhost MCP server to ChatGPT, Codex, the Responses API and AgentKit through an OpenAI-hosted tunnel endpoint, without exposing the server to the public internet.
tunnel-client is meant for an MCP server that lives on a laptop, a VM, a Kubernetes cluster or a private network that needs to be reached by an OpenAI-hosted product, when a new inbound firewall rule or a public endpoint is not an option. It runs as an operator-visible daemon with /healthz, /readyz, /metrics and a /ui endpoint before a connector or API call depends on it.
A runtime API key and tunnel ID let it run a built-in server_info, echo and uppercase demo without a separate MCP server, using stateless MCP handling. Client capability negotiation is exposed through a common X-Tunnel-Client-Capabilities header, and a Go SDK with an in-memory transport lets an MCP server be embedded directly in a Go process.
It is written in Go, and its documentation covers its architecture and trust boundary, permission roles and tunnel IDs, Docker, Kubernetes and VM deployment, and building a compatible client in another language against its published protocol and OpenAPI spec.