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.

go get github.com/openai/tunnel-client

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

Install with Homebrew

Install tunnel-client from the official OpenAI tap:

brew install openai/tools/tunnel-client

Verify the installed version, then start with the guided setup:

tunnel-client --version
tunnel-client help quickstart

The Formula installs the matching tunnel-client, bundled cloudflared, and companion manifest together, while exposing only the tunnel-client command. For Docker, Kubernetes, or VM deployments, see docs/deployment/overview.md.

To generate the shareable guide output locally:

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

For Codex / 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:

CONTROL_PLANE_TUNNEL_ID: create or inspect it in Tunnels management, or via tunnel-client admin tunnels create|list|get ... with OPENAI_ADMIN_KEY.
CONTROL_PLANE_API_KEY: create it in Runtime API keys; this is the key used by tunnel-client doctor and tunnel-client run.
OPENAI_ADMIN_KEY: 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 CONTROL_PLANE_API_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 sample_mcp_enterprise_proxy
tunnel-client init --sample sample_mcp_stdio_local --profile local-stdio --tunnel-id tunnel_0123456789abcdef0123456789abcdef --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 CONTROL_PLANE_TUNNEL_ID and a separate runtime key as CONTROL_PLANE_API_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 ./...

SBOMs

The public repository includes deterministic six-platform dependency baselines for the full client, runtime, and runtime with Cloudflared. They inventory synthetic payloads built from declared offline source and vendor snapshots, including pinned Cloudflared module versions, purls, and CPEs. Do not hand-edit them; maintainers refresh them through the hermetic SBOM generation check when dependency inputs or a Cloudflared pin changes. The baselines are useful for dependency review and drift detection, but they do not claim that a public release ZIP contains the same bytes.

From a checkout of this public repository, verify that the mirrored baseline files match their mirrored manifest before importing them into a dependency scanner:

./scripts/verify_sbom_baselines.sh

That command proves the checkout's three baseline documents match compliance/sbom-baseline-manifest.json and parse as SPDX 2.3. It does not prove that any release archive contains those bytes.

Validate a downloaded release

Releases produced by the current release workflow publish a matching SPDX 2.3 sidecar for each ZIP, embed the same sidecar in the ZIP, and cover both files in SHA256SUMS.txt. Older releases without .spdx.json sidecars cannot be artifact-validated this way. Use the release sidecar, not a checked-in baseline, to validate downloaded bytes.

From a checkout of this public repository at the matching release tag, replace the example tag and choose one of client, runtime, or runtime-cloudflared. The commands require Bash, Python 3, curl, and the GitHub CLI:

release=vX.Y.Z
platform=linux-amd64
flavor=runtime
prefix=tunnel-client-runtime
stem="${prefix}-${release}-${platform}"
base="https://github.com/openai/tunnel-client/releases/download/${release}"

curl -fLO "${base}/${stem}.zip"
curl -fLO "${base}/${stem}.spdx.json"
curl -fLO "${base}/SHA256SUMS.txt"

gh attestation verify "${stem}.zip" \
  --repo openai/tunnel-client \
  --signer-workflow openai/tunnel-client/.github/workflows/release.yml \
  --source-ref "refs/tags/${release}"
gh attestation verify "${stem}.spdx.json" \
  --repo openai/tunnel-client \
  --signer-workflow openai/tunnel-client/.github/workflows/release.yml \
  --source-ref "refs/tags/${release}"
gh attestation verify SHA256SUMS.txt \
  --repo openai/tunnel-client \
  --signer-workflow openai/tunnel-client/.github/workflows/release.yml \
  --source-ref "refs/tags/${release}"

./scripts/verify_release_archive.sh \
  --flavor "${flavor}" \
  --archive "${stem}.zip" \
  --sbom "${stem}.spdx.json" \
  --checksums SHA256SUMS.txt

Use prefix=tunnel-client with flavor=client, or prefix=tunnel-client-runtime-cloudflared with flavor=runtime-cloudflared. The attestation checks establish that the ZIP, sidecar, and checksum file came from this repository's release workflow. The archive verifier then fails closed when the published checksums do not match, the ZIP is too large or has unsafe, duplicate, or non-regular members, its embedded sidecar differs from the downloaded sidecar, or the SPDX SHA256 inventory does not match the extracted payload. After it passes, import the matching .spdx.json file into the dependency scanner of your choice. Runtime releases also publish a matching *-scan-manifest.json that binds scanner scope, source archives, license evidence, and the release sidecars.

Build the CLI binary from a source checkout. The Make target stamps the checkout Git SHA into the version sent in User-Agent and X-Tunnel-Client-Version:

make admin-ui
make tunnel-client
./bin/tunnel-client help quickstart

If you invoke Go directly, stamp the same metadata explicitly:

module_path="$(go list -m -f '{{.Path}}')"
git_sha="$(git rev-parse HEAD)"
mkdir -p bin

go build \
  -ldflags "-X ${module_path}/pkg/version.GitSHA=${git_sha}" \
  -o bin/tunnel-client \
  ./cmd/client

Narrow runtime artifacts

tunnel-client-runtime and tunnel-client-runtime-cloudflared are the runtime-only customer surfaces. They intentionally expose only run plus flag-based --help and --version; use the full tunnel-client binary for onboarding, admin, Codex, and profile-management commands. The Cloudflare flavor adds only the approved cloudflared.* settings and supervises a pinned cloudflared companion.

Build either binary from a source checkout with its Make target (the shorter aliases are equivalent):

make tunnel-client-runtime              # alias: make runtime
make tunnel-client-runtime-cloudflared  # alias: make runtime-cloudflared

The targets write platform-specific binaries under bin/<goos>_<goarch>/ and stable paths at bin/tunnel-client-runtime and bin/tunnel-client-runtime-cloudflared (.exe on Windows). Inspect the exact runtime flags with ./bin/tunnel-client-runtime run --help or ./bin/tunnel-client-runtime-cloudflared run --help.

Run the narrow runtime against an HTTP MCP server:

export CONTROL_PLANE_API_KEY='...'
export CONTROL_PLANE_TUNNEL_ID='tunnel_0123456789abcdef0123456789abcdef'
export MCP_SERVER_URL='https://mcp.example.com/mcp'
./bin/tunnel-client-runtime run

For managed Cloudflare provisioning, use the Cloudflare flavor. Release archives place the pinned cloudflared executable beside the runtime; for a source-only build, point to an existing companion explicitly:

./bin/tunnel-client-runtime-cloudflared run \
  --cloudflared.managed \
  --cloudflared.path /path/to/cloudflared

To build the corresponding Linux images, use make build-image-runtime and make build-image-runtime-cloudflared; the Cloudflare image includes its pinned companion and both images use run as their entrypoint.

Contributors can run the compatibility suite with make test-runtime. Its host-binary checks compare the full client and runtime flavors with the same profile bytes, environment, flags, local control-plane/MCP/OAuth/proxy/TLS fixtures, and shutdown signal. The same target also packages native release-shaped ZIPs and checks that they verify, extract, identify the expected flavor, and expose run --help; that ZIP smoke is not a second fake-service parity run.

After building the runtime images, make runtime-container-compatibility runs a deployment smoke for their default and overridden entrypoints with read-only profile/Secret mounts and hardened container settings. It uses intentionally unreachable local endpoints to check startup surfaces and SIGTERM, not to compare image behavior with the full client or assert /readyz readiness. An optional local Kubernetes deployment smoke is available with TUNNEL_CLIENT_RUNTIME_K8S_COMPAT=1 make runtime-k8s-compatibility; it requires Docker plus kind or k3d, checks the runtime Pods' mounted profile/Secret and /healthz surface, and does not contact external services.

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. Source-checkout builds made with the Make target or explicit linker flag above append the Git SHA to that semantic version.

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
TUNNEL_MANAGEMENT_DIAGNOSTICS=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 client_instance_id, 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 CONTROL_PLANE_CLIENT_CERT / CONTROL_PLANE_CLIENT_KEY). 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 MCP_STARTUP_WAIT_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 client_instance_id, 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/build_admin_ui.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 TUNNEL_ENGINE_REDIS_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.
sample_mcp_enterprise_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 organization_ids / workspace_ids 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.

Name		Name	Last commit message	Last commit date
.codex/environments		.codex/environments
.github/workflows		.github/workflows
adminui		adminui
cmd		cmd
compliance		compliance
docs		docs
e2e		e2e
examples		examples
pkg		pkg
plugins		plugins
scripts		scripts
testsupport		testsupport
wrappers/mcp-tunnel-client-proxy		wrappers/mcp-tunnel-client-proxy
.dockerignore		.dockerignore
.gitattributes		.gitattributes
.gitignore		.gitignore
Dockerfile		Dockerfile
Dockerfile.runtime		Dockerfile.runtime
LICENSE		LICENSE
MODULE.bazel.in		MODULE.bazel.in
Makefile		Makefile
NOTICE		NOTICE
README.md		README.md
client.go		client.go
client_test.go		client_test.go
go.mod		go.mod
go.sum		go.sum
package.json		package.json

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