Secure MCP Tunnel client

tunnel-client is the customer-run agent behind Secure MCP Tunnel. It connects a private or localhost MCP (Model Context Protocol) server to ChatGPT, Codex, the Responses API, and AgentKit through an OpenAI-hosted MCP tunnel endpoint, while keeping the MCP server off the public internet.

Use it when:

• You have an MCP server on a laptop, VM, Kubernetes cluster, or private

network and need an OpenAI-hosted product to reach it.

• Security will not approve a new inbound firewall rule or public endpoint for

the MCP server.

• You want an operator-visible daemon with /healthz, /readyz, /metrics,

and /ui before a connector or API call depends on it.

If you searched for "secure MCP tunnel", "MCP tunnel ChatGPT", "connect local MCP server to ChatGPT", "connect local MCP server to Codex", "localhost to ChatGPT", or "Codex local MCP", start with tunnel-client help quickstart, then read the onboarding guide below.

Start Here

• **Need the shortest working path from localhost or a private MCP server to

ChatGPT or Codex?** Start with docs/onboarding.md.

• Need the customer-shareable network and trust-boundary story? Read

docs/architecture.md.

• Need roles, groups, tunnel IDs, or API keys? Read

docs/permissions.md.

• Need Docker, Kubernetes, or VM deployment guidance? Read

docs/deployment/overview.md.

• Need to debug readiness, connector discovery, or OAuth? Read

docs/troubleshooting.md.

• Building a compatible client in another language? Read

docs/protocol.md and use docs/openapi.json.

• Embedding an MCP server directly in a Go process? Use the Go SDK with

the MCP SDK's in-memory transport; see examples/go-sdk-inmemory.

Embed as a Go SDK

The module can run in the same process as a Go MCP server. The MCP server does not need to bind a port or use stdio: give the server side of an in-memory MCP transport pair to your server and the client side to tunnelclient.New.

~~~bash go get github.com/openai/tunnel-client ~~~

~~~go import ( "context"

"github.com/modelcontextprotocol/go-sdk/mcp" tunnelclient "github.com/openai/tunnel-client" )

ctx := context.Background() server := mcp.NewServer(&mcp.Implementation{Name: "my-server", Version: "1.0.0"}, nil) serverTransport, tunnelTransport := mcp.NewInMemoryTransports() go server.Run(ctx, serverTransport)

client, err := tunnelclient.New(tunnelclient.Config{ TunnelID: "tunnel_0123456789abcdef0123456789abcdef", APIKey: apiKey, }, tunnelTransport) if err != nil { return err } return client.Run(ctx) ~~~

The runnable Go SDK example registers an echo tool and connects it to the OpenAI Tunnel control plane.

Documentation Map

• Public Secure MCP Tunnel guide:

developers.openai.com/api/docs/guides/secure-mcp-tunnels

• Shareable end-user guide: docs/end-user-guide.md
• Start here: docs/onboarding.md
• Permissions, roles, and groups: docs/permissions.md
• Architecture diagrams: docs/architecture.md
• Connector behavior: docs/connectors.md
• Wire protocol for client implementers: docs/protocol.md
• OpenAPI contract: docs/openapi.json
• Enterprise customer handoff:

docs/enterprise-customer-onboarding.md

• Configuration reference: docs/configuration.md
• Deployment guides: docs/deployment/overview.md
• Bundled Cloudflare companion:

docs/deployment/cloudflared.md

• Troubleshooting: docs/troubleshooting.md
• Development & testing: docs/development.md
• In-memory Go SDK example:

examples/go-sdk-inmemory

• Roadmap / design notes: docs/roadmap.md

Homebrew publication tooling

Homebrew installation is not generally available until a compatible stable Formula is present in the tap. For approved private-CI release automation, scripts/publishlatesthomebrew_formula.sh reads the latest published stable release, renders the Formula from its public checksum manifest, and opens a Formula-only pull request in openai/homebrew-tools; it never merges that PR.

The wrapper keeps release reads separate from tap writes:

• TUNNELCLIENTRELEASEREADTOKEN is an optional read-only GitHub token for

the public release lookup.

• OPENAIGITHUBINSTALLATIONTOKENFILE is the preferred private-CI input:

a mounted GitHub App installation-token JSON file scoped to openai/homebrew-tools with only contents:write and pullrequests:write. OPENAIGITHUBINSTALLATIONTOKEN_JSON remains available for local testing.

Run it only from the approved private publisher path:

TUNNELCLIENTRELEASEREADTOKEN=<read-only-github-token> \
OPENAIGITHUBINSTALLATIONTOKENFILE=/etc/secrets/github-installation-token/token-json \
bash ./scripts/publishlatesthomebrew_formula.sh

See docs/development.md for the local test command and the availability boundary.

To generate the shareable guide output locally:

make end-user-guide-screenshots
make end-user-guide-html
make end-user-guide-slides

For Codex / Claude / Copilot

If you want the shortest supported path from a local or localhost MCP server to ChatGPT or Codex, start with tunnel-client help quickstart. For Codex plugin lifecycle work, use the native tunnel-client runtimes ... and tunnel-client admin-profiles ... command trees surfaced by tunnel-client help plugin.

Supervision choice:

• Use tunnel-client run ... when you intentionally want a foreground daemon

attached to the current terminal.

• For a long-lived local runtime managed by Codex, prefer

tunnel-client runtimes connect .... Do not use nohup or disown as the tunnel-client supervision path.

• After runtimes connect, check tunnel-client runtimes status <alias>

before reporting success. Only report success when status shows the managed runtime running with health reported. Use --json when Codex needs the explicit process_running, healthy, and ready fields.

Use these exact setup pages during first use:

• Tunnels management and supported tunnel-client download:

https://platform.openai.com/settings/organization/tunnels

• Organization roles: https://platform.openai.com/settings/organization/people/roles
• Organization groups: https://platform.openai.com/settings/organization/people/groups
• Runtime API keys: https://platform.openai.com/settings/organization/api-keys
• Admin API keys: https://platform.openai.com/settings/organization/admin-keys
• ChatGPT connector settings: https://chatgpt.com/#settings/Connectors

Which value comes from where:

• CONTROLPLANETUNNEL_ID: create or inspect it in Tunnels management, or via

tunnel-client admin tunnels create|list|get ... with OPENAIADMINKEY.

• CONTROLPLANEAPI_KEY: create it in Runtime API keys; this is the key used

by tunnel-client doctor and tunnel-client run.

• OPENAIADMINKEY: only for tunnel-client admin tunnels

list|create|update|delete. Do not use the admin key for the long-lived daemon.

Required tunnel permissions:

• Runtime users and the principal that creates CONTROLPLANEAPI_KEY need

Tunnels Read + Use.

• Tunnel managers need Tunnels Read + Manage, plus Use if they also

run the daemon or attach ChatGPT connectors.

• Admin-key creators need the Platform admin-key permission in addition to any

tunnel permissions they need.

See docs/permissions.md for the group/role workflow and screenshots.

Binary-first flow:

tunnel-client help quickstart
tunnel-client profiles samples list
tunnel-client profiles samples show samplemcpenterprise_proxy
tunnel-client init --sample samplemcpstdiolocal --profile local-stdio --tunnel-id tunnel0123456789abcdef0123456789abcdef --mcp-command "python /path/to/server.py"
tunnel-client doctor --profile local-stdio --explain
tunnel-client run --profile local-stdio
tunnel-client run --profile-file ./profiles/local-stdio.yaml

If you need the tunnel id or runtime/admin keys first, open the matching URL above before running init. If your rollout has self-serve tunnel access, create the tunnel yourself in Tunnels management or with tunnel-client admin tunnels create, then export the returned id as CONTROLPLANETUNNEL_ID and a separate runtime key as CONTROLPLANEAPI_KEY. Create or verify the connector from the ChatGPT settings URL above only while tunnel-client run ... is healthy, and keep the daemon running for connector discovery and every MCP call from ChatGPT.

The Platform Tunnels page download button is sourced from tunnel-service's gated tunnel metadata response. When a new public tunnel-client release becomes the supported download, update tunnel-service's hard-coded public artifact URL alongside the release handoff.

Validate a source checkout with native Go tooling:

go build ./...
go test ./...

Build the CLI binary:

make admin-ui
go build -o bin/tunnel-client ./cmd/client
./bin/tunnel-client help quickstart

Public releases use plain semantic-version tags such as v0.0.10. Source archives from release tags carry the release version in pkg/version/VERSION. A plain go build from a downloaded release .tar.gz therefore reports the tag semantic version through tunnel-client --version, User-Agent, and the explicit control-plane version headers.

Supported release archives also bundle pinned cloudflared 2026.7.2 beside the CLI for Linux amd64/arm64, macOS amd64/arm64, and Windows amd64/arm64. Official release images are published at ghcr.io/openai/tunnel-client for Linux amd64 and arm64; they bundle the matching companion. Pin an exact vX.Y.Z tag or digest for production. Stable releases also update the X.Y and latest aliases; prereleases do not. For a logical tunnel created with managed Cloudflare provisioning, let the authenticated client fetch the runtime token and start the companion without distributing a static token:

tunnel-client run \
  --cloudflared.managed \
  --control-plane.tunnel-id tunnel_0123456789abcdef0123456789abcdef \
  --mcp.server-url https://mcp.example.com/mcp

For a pre-provisioned Cloudflare tunnel, a static token remains available as an explicit override and is never put in argv:

export CLOUDFLARED_TOKEN='...'
tunnel-client run \
  --cloudflared.token env:CLOUDFLARED_TOKEN \
  --control-plane.tunnel-id tunnel_0123456789abcdef0123456789abcdef \
  --mcp.server-url https://mcp.example.com/mcp

See docs/deployment/cloudflared.md for platform coverage, readiness/failure behavior, Go module provenance, and security-update ownership.

If an operator intentionally runs cloudflared without tunnel-client, print a token-free production config and keep the token in a separate secret file:

tunnel-client cloudflared config \
  --token-file /run/secrets/cloudflared/token \
  > /etc/cloudflared/config.yml
TUNNELMANAGEMENTDIAGNOSTICS=false \
  cloudflared tunnel --config /etc/cloudflared/config.yml run

Fastest Codex terminal path:

tunnel-client codex assistant "Summarize what tunnel-client is doing in this checkout."
tunnel-client codex status
tunnel-client codex plugin install
tunnel-client runtimes list
tunnel-client help plugin
tunnel-client codex plugin uninstall

Choose the raw binary when you want the smallest possible setup surface. Choose tunnel-client codex assistant when you want the fastest Codex-native terminal path. Choose the plugin when you want a Codex-local entrypoint over the native runtimes / admin-profiles command trees.

Starter prompts for Codex:

• Figure out what tunnel-client is for from the binary help, then get me to /ui with the shortest local path.
• I only have the source checkout. Figure out how to build tunnel-client, then get me to /ui with the shortest local path.
• Use tunnel-client to create or reuse a profile, run doctor --explain, and then start the foreground daemon attached to this terminal.
• Run tunnel-client codex assistant and summarize what this checkout is for in one sentence.
• Install the Codex plugin from the tunnel-client binary, connect the provided tunnel id, and tell me whether the runtime is launched, healthy, or ready.
• For a long-lived local runtime, use tunnel-client runtimes connect to attach the provided tunnel id, then run tunnel-client runtimes status <alias> before reporting whether the runtime is launched, healthy, or ready.

What it does

• The client long-polls the OpenAI tunnel control plane over HTTPS:

- GET /v1/tunnels/{tunnel_id}/poll - POST /v1/tunnels/{tunnel_id}/response

• Older tunnel-client releases may still use the singular /v1/tunnel/...

aliases. Tunnel-service keeps those aliases during migration; removing them, if ever desired, is a separate later cleanup after telemetry shows no remaining legacy clients.

• Control-plane requests include User-Agent: oai-tunnel-client/<version> for

compatibility, plus explicit X-Tunnel-Client-Name and X-Tunnel-Client-Version headers for service-side logs and metrics. Each process also generates a new opaque clientinstanceid, sends it as X-Tunnel-Client-Instance-Id, and includes it in structured logs and the local admin UI for request correlation.

• Control-plane HTTPS requests can present a separate client certificate/key

pair using --control-plane.client-cert and --control-plane.client-key (or CONTROLPLANECLIENTCERT / CONTROLPLANECLIENTKEY). When those are configured with the default https://api.openai.com host, the client automatically uses https://mtls.api.openai.com for control-plane calls.

• On startup, it fetches tunnel metadata for operator visibility:

- GET /v1/tunnels/{tunnel_id}

• It forwards received JSON-RPC requests to your configured MCP server over

Streamable HTTP, stdio, or in-memory transport, and relays explicit Streamable HTTP session termination requests when the control plane receives DELETE /v1/mcp/{tunnel_id}.

• It routes commands by channel: main targets the configured MCP binding,

additional configured channels can target their own MCP bindings, and harpoon is routable only when Harpoon has registered targets.

• On startup, it fetches OAuth Protected Resource Metadata from the MCP server

for diagnostics.

• For sidecar deployments whose local MCP listener may bind after

tunnel-client starts, the optional MCPSTARTUPWAIT_TIMEOUT gate delays the first control-plane poll and OAuth discovery until the main MCP listener is reachable.

• For OAuth auth-server handling, authorization_servers[0] from PRMD is the

only source of truth and metadata fetch target.

• Metadata is accepted even when issuer differs from

authorization_servers[0] (external IdP issuer URLs are supported), with mismatch diagnostics preserved in logs/state.

• It exposes an admin/health server (/healthz, /readyz, /metrics) and

a lightweight admin UI (/ui) for operational status.

• The admin UI Overview reports the process-scoped clientinstanceid,

channel availability, and reasons when channels are disabled.

• The admin UI Logs tab can switch the live runtime log level between debug,

info, and warn without restarting the process.

• The admin UI log export returns a redacted support bundle with recent logs

plus a point-in-time Prometheus snapshot from /metrics and a redacted runtime YAML snapshot containing argv, relevant environment, actual YAML config, and effective config.

• It embeds the Harpoon MCP server to provide a labeled, allowlisted

outbound HTTP client for internal tooling.

Admin UI build notes

The admin UI assets under pkg/adminui/assets are generated from the TypeScript/Svelte source in adminui/. To rebuild them locally:

./scripts/buildadminui.sh ./adminui ./pkg/adminui/assets
or
make admin-ui

CLI

• tunnel-client shows help and available subcommands.
• tunnel-client help <topic> shows embedded task-oriented help for

quickstart, samples, doctor, oauth, and plugin.

• tunnel-client codex assistant [prompt...] starts a terminal assistant

session through the supervised codex app-server, using prompt args for one-shot mode and TTY stdin for REPL mode. It defaults to medium reasoning effort, and the REPL supports /model to inspect or change model and reasoning without restarting.

• tunnel-client codex status|install|upgrade|uninstall inspects local Codex

CLI/app-server availability and prints the official install/upgrade/remove commands.

• tunnel-client codex plugin install|uninstall|export installs, removes, or

exports the embedded Tunnel MCP plugin bundle.

• tunnel-client dev mcp-stub runs an embedded demo MCP + OAuth metadata server

for one-binary end-to-end validation.

• tunnel-client dev proxy runs a local control plane plus tunnel-client for

integration tests. TCP ingress is the default and prints mcp_url; pass --listen-unix-socket PATH for external MCP ingress over a Unix socket. Its --backend auto|go|rust flag defaults to auto, and --engine-queue-backend inmem|redis defaults to inmem. Ordinary public builds use the Go in-memory backend; rust and Redis require a binary with the optional linked Rust adapter. Redis also needs --engine-redis-url or TUNNELENGINEREDIS_URL.

• tunnel-client init writes a validated first-use profile.
• tunnel-client doctor validates config and explains what is missing before

startup.

• tunnel-client profiles samples list|show exposes built-in sample profiles.
• samplemcpenterprise_proxy is the built-in starter for outbound proxies

and private PKI, with env-backed proxy and CA bundle references.

• tunnel-client admin-profiles list|set|delete manages saved admin-key

profiles for native runtime workflows.

• tunnel-client runtimes create|connect|list|status|stop|rm manages native

alias state and local runtime supervision.

• tunnel-client run starts the foreground/manual client poller attached to

the current terminal.

• tunnel-client cloudflared version prints the bundled companion pin,

upstream release, and security-patch owner without starting a process.

• tunnel-client cloudflared config --token-file <path> prints a token-free

production cloudflared config for operators who run cloudflared directly.

• tunnel-client admin tunnels get <id> is the read-only metadata lookup used

on the runtime-user path; broader admin tunnels CRUD still requires an admin key. When you need admin CRUD scope, inspect the returned organizationids / workspaceids from tunnel-client admin --json tunnels get <id> and reuse those live values instead of guessing ids.

License

This project is licensed under the Apache License 2.0.