# 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.
This CLI and its [Go SDK](#embed-as-a-go-sdk) run beside your private MCP server.
Applications call the OpenAI-hosted `/v1/mcp/{tunnel_id}` endpoint through their
MCP transport; the runtime receives those requests and delivers responses.
The poll/response endpoints are the runtime's queue protocol for client
implementers. See the [architecture](docs/architecture.md) for the request flow
and the [protocol](docs/protocol.md) when building a compatible runtime.
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
- **Selecting a regional control-plane endpoint?** Use
`--control-plane.residency`, `CONTROL_PLANE_RESIDENCY`, or YAML
`control_plane.residency`. See the [endpoint catalog and mTLS settings](docs/configuration.md#residency-endpoint-selection).
Endpoint selection is independent of regional Tunnel service availability.
- **Need the shortest working path from localhost or a private MCP server to
ChatGPT or Codex?** Start with [`docs/onboarding.md`](docs/onboarding.md).
- **Need the customer-shareable network and trust-boundary story?** Read
[`docs/architecture.md`](docs/architecture.md).
- **Need roles, groups, tunnel IDs, or API keys?** Read
[`docs/permissions.md`](docs/permissions.md).
- **Need Docker, Kubernetes, or VM deployment guidance?** Read
[`docs/deployment/overview.md`](docs/deployment/overview.md).
- **Need to debug readiness, connector discovery, or OAuth?** Read
[`docs/troubleshooting.md`](docs/troubleshooting.md).
- **Building a compatible client in another language?** Read
[`docs/protocol.md`](docs/protocol.md) and use
[`docs/openapi.json`](docs/openapi.json). Optional client features use the
common [`X-Tunnel-Client-Capabilities` header](docs/protocol.md#tunnel-client-capabilities).
- **Upgrading for server-directed polling placement?** Read the
[routing correction and activation notes](docs/routing-correction.md).
Supporting clients work with existing services immediately; corrections are
enabled separately after client release. No configuration change is needed.
- **Using MCP timing or distributed tracing?** Read the
[timing release and rollback guidance](docs/configuration.md#response-timing-compatibility).
Trace forwarding is disabled by default; opt in with
`--mcp.forward-trace-context` to carry W3C trace context in MCP `params._meta`
over stdio and Streamable HTTP.
Opt-in [local span export](docs/configuration.md#local-tracing) uses
`--tracing.enabled --tracing.file=/private/new-trace.jsonl`. Complete traces
require compatible service queue handoff and caller parent propagation first.
- **Forwarding the original HTTP request ID?** MCP HTTP forwarding is enabled
by default. Use `--forward-request-id=mcp,harpoon` to include Harpoon REST
requests, `--forward-request-id=mcp,oauth` to include eligible queued OAuth
discovery requests, or `--forward-request-id=none` to disable
automatic forwarding.
The same setting is available as `FORWARD_REQUEST_ID` or top-level YAML
`forward_request_id`; see [request ID forwarding](docs/configuration.md#request-id-forwarding).
- **Using a namespaced tunnel ID?** Preserve the full ID returned by the service.
The client accepts legacy IDs and aliases with a four-character namespace;
see [tunnel identifiers](docs/protocol.md#scope).
- **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`](examples/go-sdk-inmemory).
## Try the embedded demo
With a runtime API key and tunnel ID, run the built-in `server_info`, `echo`,
and `uppercase` tools without a separate MCP server:
```bash
export CONTROL_PLANE_API_KEY="sk-..."
export CONTROL_PLANE_TUNNEL_ID="tunnel_0123456789abcdef0123456789abcdef"
tunnel-client run --embedded-stateless-mcp-stub --health.listen-addr 127.0.0.1:0
```
`--embedded-stateless-mcp-stub` uses stateless MCP handling even when a client
sends `initialize` and `notifications/initialized`. It issues no MCP session
ID, and these demo tools do not require MCP session affinity between processes.
OAuth and application state have separate requirements.
`--embedded-mcp-stub` keeps its existing compatibility behavior: legacy
initialization and session requests use stateful handling; self-contained
modern discovery and tool requests use stateless handling. Choose one embedded
mode per run. Both share the embedded listen-address, Unix-socket, server-name, and
server-version options; see [embedded demo configuration](docs/configuration.md#embedded-demo-mcp-modes)
for defaults and target conflicts.
## 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](examples/go-sdk-inmemory) 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`](https://developers.openai.com/api/docs/guides/secure-mcp-tunnels)
- **Shareable end-user guide**: [`docs/end-user-guide.md`](docs/end-user-guide.md)
- **Start here**: [`docs/onboarding.md`](docs/onboarding.md)
- **Permissions, roles, and groups**: [`docs/permissions.md`](docs/permissions.md)
- **Architecture diagrams**: [`docs/architecture.md`](docs/architecture.md)
- **Connector behavior**: [`docs/connectors.md`](docs/connectors.md)
- **Wire protocol for client implementers**: [`docs/protocol.md`](docs/protocol.md)
- **OpenAPI contract**: [`docs/openapi.json`](docs/openapi.json)
- **Enterprise customer handoff**:
[`docs/enterprise-customer-onboarding.md`](docs/enterprise-customer-onboarding.md)
- **Configuration reference**: [`docs/configuration.md`](docs/configuration.md)
- **Deployment guides**: [`docs/deployment/overview.md`](docs/deployment/overview.md)
- **Bundled Cloudflare companion**:
[`docs/deployment/cloudflared.md`](docs/deployment/cloudflared.md)
- **Troubleshooting**: [`docs/troubleshooting.md`](docs/troubleshooting.md), including
[DNS diagnostic logs for Android / Termux](docs/troubleshooting.md#dns-failures-and-android--termux).
- **Development & testing**: [`docs/development.md`](docs/development.md)
- **In-memory Go SDK example**:
[`examples/go-sdk-inmemory`](examples/go-sdk-inmemory)
- **Roadmap / design notes**: [`docs/roadmap.md`](docs/roadmap.md)
## Install with Homebrew
On macOS, Homebrew is the supported installation path. Directly downloaded
release ZIPs are not currently notarized and can be blocked by Gatekeeper. If
a manually downloaded archive is blocked, do not use `xattr`, `spctl`, or
**Open Anyway** to bypass the check; install from the official OpenAI tap
instead:
```bash
brew install openai/tools/tunnel-client
```
Verify the installed version, then start with the guided setup:
```bash
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. It also installs Bash, Zsh, and Fish completions for that version.
If your shell does not load them automatically, follow
[Homebrew's shell completion setup](https://docs.brew.sh/Shell-Completion).
For Docker, Kubernetes, or VM deployments, see
[`docs/deployment/overview.md`](docs/deployment/overview.md).
To generate the shareable guide output locally:
```bash
make end-user-guide-screenshots
make end-user-guide-html
make end-user-guide-slides
```
### Start at macOS login
The Homebrew Formula supports `brew services`. It supervises
`tunnel-client run` using the profile at
`$(brew --prefix)/etc/tunnel-client.yaml`, starts at login, and restarts the
runtime after it exits. Installation and upgrades do not create or replace
that profile.
First, select the profile you already configured. If it belongs to a managed
alias, find its `profile_path` with `tunnel-client runtimes status <alias> --json`,
then run `tunnel-client runtimes stop <alias>` before starting the service.
Copy the profile to the service location, preserving your custom settings:
```bash
service_profile="$(brew --prefix)/etc/tunnel-client.yaml"
if [ -e "$service_profile" ]; then
cp -p "$service_profile" "$service_profile.backup.$(date +%Y%m%d%H%M%S)"
fi
install -m 600 /absolute/path/to/existing-profile.yaml "$service_profile"
```
Use absolute paths in this profile, including paths to MCP executables,
working directories, and secret files. The service includes Homebrew's `bin`
and `sbin` on `PATH`, but does not load your interactive shell configuration.
Replace shell-only `env:` references with persistent references such as this
existing profile field:
```yaml
control_plane:
api_key: file:/Users/YOU/.config/tunnel-client/runtime.key
```
Store the runtime API key in that file with permissions `0600`; keep its
directory private too. The service definition contains the profile path,
not the key. Validate the profile, then start the service as your logged-in
user, without `sudo`:
```bash
tunnel-client doctor --profile-file "$(brew --prefix)/etc/tunnel-client.yaml"
brew services start openai/tools/tunnel-client
brew services info openai/tools/tunnel-client
tunnel-client health --url http://127.0.0.1:8080 --json
```
The health command above uses the default listener. If your profile configures
a different health address or a `health.url_file`, use that address or
`health --url-file /absolute/path/to/health-url` instead. An active service
alone does not mean the tunnel is ready. Inspect
`$(brew --prefix)/var/log/tunnel-client.log` and any `log.file` destination in
your profile if startup fails.
Use Homebrew to manage this runtime:
```bash
# Reload the profile/key or pick up the installed version after a brew upgrade.
brew services restart openai/tools/tunnel-client
# Stop the runtime and disable automatic login startup.
brew services stop openai/tools/tunnel-client
```
The service uses Homebrew's stable `opt` path across upgrades. The CLI's
`runtimes status` and `runtimes stop` commands manage its own detached
processes; they do not discover or control the Homebrew service. Do not run
`runtimes connect` for the same tunnel while the service is active: that
command writes a generated profile and starts a separate runtime. Stop the
service before switching back to CLI management. Keep only one runtime active
for the tunnel during the switch, especially for stdio or stateful MCP servers.
The per-user macOS service runs during your login session, not before login
or after logout. Sleep suspends the Mac's work; wake allows the runtime's
network retries to resume. Homebrew's launchd service restarts an exited
process, but does not restart one merely because readiness fails. Start a
local HTTP MCP server through its own supervisor. For a server that starts
later, set `mcp.startup_wait_timeout` (for example, `2m`) in the profile to
allow startup connection retries. If that window expires, restart the service
after the MCP server is available; the process can remain alive with its
startup probe failed. After a server restart, check readiness and logs;
existing MCP sessions may need to be initialized again. For a stdio target,
the runtime owns the MCP child. Do not assume interrupted tool calls are
replayed. See [Supervising startup](docs/health.md#supervising-startup) for
interpreting process liveness, OAuth discovery, readiness, and polling state.
## 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 ...` for a foreground daemon attached to the current
terminal or supervised by the OS; see [macOS login startup](#start-at-macos-login).
- 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`.
- For [AWS workload identity](docs/configuration.md#aws-workload-identity), set
`CONTROL_PLANE_AWS_IDENTITY_PROVIDER_ID` and `CONTROL_PLANE_AWS_SERVICE_ACCOUNT_ID`.
- `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`](docs/permissions.md) for the group/role workflow
and screenshots.
Binary-first flow:
```bash
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
```
**Stdio deployment limit:** run only one active `tunnel-client` instance per
tunnel ID when using `--mcp.command` / `MCP_COMMAND`. Multiple active instances
sharing that tunnel ID are **not supported**, including overlap during a
restart. Each instance launches a separate MCP child, and initialization and
later requests can reach different children. Stop the old instance before
starting its replacement, or use distinct tunnel IDs for independent instances.
See [stdio deployment limits](docs/configuration.md#stdio-deployment-limits).
By default, `tunnel-client` restarts a supervised stdio child after an
unexpected exit, stdout EOF, or stdin write failure. Calls in progress may
fail, and legacy callers must initialize the replacement child before retrying.
If your deployment uses an external process supervisor to restart the whole
client, set `--mcp.stdio-failure-policy=exit`,
`MCP_STDIO_FAILURE_POLICY=exit`, or YAML `mcp.stdio_failure_policy: exit`.
That setting restores nonzero client exit on these failures; intentional
shutdown still exits successfully. Remove the new flag or YAML key before
downgrading to a version that does not recognize it.
Stdio initialization is checked automatically. Legacy calls require a successful
`initialize` exchange followed by `notifications/initialized`; premature calls
return `mcp_initialization_required` immediately. Self-contained MCP requests
using protocol version `2026-07-28` or later pass through without a handshake.
The caller owns initialization, including after child replacement. See
[configuration](docs/configuration.md#mcp-server) for lifecycle behavior.
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:
```bash
go build ./...
go test ./...
```
Independent tests, subtests, and fuzz seed cases use `t.Parallel()`. Give each
case its own mutable fixtures, and use `t.Cleanup` for resources shared by
parallel children. Keep dependent state transitions in one test. Keep tests
that mutate process-wide globals, environment variables, signals, or stdio
serial.
Check concurrent execution with the race detector and shuffled test order:
```bash
go test -race -shuffle=on -count=3 ./...
```
The E2E and mock-server packages default to two concurrent tests to bound
resource use. An explicit `-parallel=N` overrides that default.
## SBOMs
The public repository includes deterministic six-platform dependency baselines
for the
[full client](https://github.com/openai/tunnel-client/blob/master/compliance/tunnel-client.spdx.json),
[runtime](https://github.com/openai/tunnel-client/blob/master/compliance/tunnel-client-runtime.spdx.json),
and
[runtime with Cloudflared](https://github.com/openai/tunnel-client/blob/master/compliance/tunnel-client-runtime-cloudflared.spdx.json).
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:
```bash
./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, cover both files in
`SHA256SUMS.txt`, and publish the workflow's signed Sigstore provenance bundle.
They also publish:
- `tunnel-client-vX.Y.Z-vulnerability-report.json`, generated by a
checksum-pinned Grype binary from exactly 18 release-specific SPDX sidecars:
three flavors across six platforms, each bound to its matching ZIP and
license-report SHA256, with the exact vulnerability-database SHA256 recorded;
- `tunnel-client-vX.Y.Z.openvex.json` only when the scan has findings, with
every automated statement set to `under_investigation` rather than claiming
that a finding is fixed, exploitable, or not affected; and
- `tunnel-client-vX.Y.Z-enterprise-evidence.json`, which inventories the
release evidence bytes, scanner/database identity, scan scope, and
provenance boundary.
The vulnerability report explicitly records OCI images as `not_scanned`:
the release contract has multi-architecture OCI index digests, not exact
per-platform OCI manifest scan inputs. Every pre-bundle release artifact is
covered by `SHA256SUMS.txt`, `PUBLIC_URLS.txt`, and the signed provenance
bundle. The bundle is intentionally excluded from its own checksum and
signature subject set.
Older releases without `.spdx.json` sidecars cannot be archive/SBOM-validated
this way; releases without a `*-provenance.sigstore.json` bundle cannot be
provenance-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:
```bash
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/${release}"
bundle="tunnel-client-${release}-provenance.sigstore.json"
source_digest="$(git rev-parse HEAD)"
curl -fLO "${base}/${stem}.zip"
curl -fLO "${base}/${stem}.spdx.json"
curl -fLO "${base}/${stem}-licenses.txt"
curl -fLO "${base}/SHA256SUMS.txt"
curl -fLO "${base}/${bundle}"
gh attestation verify "${stem}.zip" \
--bundle "${bundle}" \
--repo openai/tunnel-client \
--signer-workflow openai/tunnel-client/.github/workflows/release.yml \
--source-ref "refs/tags/${release}" \
--source-digest "${source_digest}" \
--signer-digest "${source_digest}" \
--predicate-type https://slsa.dev/provenance/v1 \
--deny-self-hosted-runners
gh attestation verify "${stem}.spdx.json" \
--bundle "${bundle}" \
--repo openai/tunnel-client \
--signer-workflow openai/tunnel-client/.github/workflows/release.yml \
--source-ref "refs/tags/${release}" \
--source-digest "${source_digest}" \
--signer-digest "${source_digest}" \
--predicate-type https://slsa.dev/provenance/v1 \
--deny-self-hosted-runners
gh attestation verify "${stem}-licenses.txt" \
--bundle "${bundle}" \
--repo openai/tunnel-client \
--signer-workflow openai/tunnel-client/.github/workflows/release.yml \
--source-ref "refs/tags/${release}" \
--source-digest "${source_digest}" \
--signer-digest "${source_digest}" \
--predicate-type https://slsa.dev/provenance/v1 \
--deny-self-hosted-runners
gh attestation verify SHA256SUMS.txt \
--bundle "${bundle}" \
--repo openai/tunnel-client \
--signer-workflow openai/tunnel-client/.github/workflows/release.yml \
--source-ref "refs/tags/${release}" \
--source-digest "${source_digest}" \
--signer-digest "${source_digest}" \
--predicate-type https://slsa.dev/provenance/v1 \
--deny-self-hosted-runners
./scripts/verify_release_archive.sh \
--flavor "${flavor}" \
--archive "${stem}.zip" \
--sbom "${stem}.spdx.json" \
--checksums SHA256SUMS.txt
```
To verify the complete release evidence set, download every asset into a clean
directory and run both fail-closed contract verifiers:
```bash
mkdir release-evidence
gh release download "${release}" \
--repo openai/tunnel-client \
--dir release-evidence
./scripts/verify_release_provenance.sh \
--bundle "release-evidence/${bundle}" \
--artifact-dir release-evidence \
--release "${release}" \
--source-digest "${source_digest}"
./scripts/verify_release_evidence.sh \
--artifact-dir release-evidence \
--release "${release}" \
--source-digest "${source_digest}"
```
Use `prefix=tunnel-client` with `flavor=client`, or
`prefix=tunnel-client-runtime-cloudflared` with
`flavor=runtime-cloudflared`. The bundle is the release workflow's signed
Sigstore evidence and supports verification without GitHub attestation lookup.
It is emitted after `SHA256SUMS.txt` is attested, so it is intentionally not
listed in that checksum file; `gh attestation verify` checks the bundle's
signature, transparency-log material, signer workflow, source ref, source
digest, and subject digest. 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.
For a fully disconnected verification environment, capture a trusted root from
an independently trusted online environment before disconnecting:
```sh
gh attestation trusted-root > trusted_root.jsonl
```
Transfer that file with the release evidence and add
`--custom-trusted-root trusted_root.jsonl` to each `gh attestation verify`
command above. The release bundle removes the GitHub attestation API
dependency; the trusted-root file removes the remaining online trust-root
lookup.
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`:
```bash
make admin-ui
make tunnel-client
./bin/tunnel-client help quickstart
```
If you invoke Go directly, stamp the same metadata explicitly:
```bash
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):
```bash
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:
```bash
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:
```bash
./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` `2026.10.2` 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:
```bash
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:
```bash
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`](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:
```bash
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:
```bash
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.`
### Complete ChatGPT setup with Codex
Copy this prompt into Codex on a computer with browser access and a terminal on
or connected to a host that can reach your private MCP server:
```text
Help me set up and verify a private Secure MCP Tunnel from my internal MCP server to ChatGPT end to end. Use browser/computer access and a terminal, following https://developers.openai.com/api/docs/guides/secure-mcp-tunnels and https://github.com/openai/tunnel-client/blob/master/docs/onboarding.md; check current UI and CLI help as you go.
First identify the intended Platform organization and ChatGPT workspace, MCP server HTTP URL or stdio command, and client host. Inspect existing tunnel, key, and ChatGPT custom MCP plugin; reuse suitable resources. Confirm tunnel organization/workspace association and permissions: tunnel creators need Tunnels Read + Manage; the restricted runtime key and plugin operator need Tunnels Read + Use. Keep literal secrets out of chat, command arguments, logs, screenshots, and config files; have me enter them locally through a secure input or environment reference.
Install the supported tunnel-client; run `tunnel-client help quickstart`, configure the server, run `tunnel-client doctor --profile <name> --explain`, start the client, and verify readiness and active polling. Keep it running for discovery and calls. In ChatGPT Plugins, add or finish a private custom MCP server with Connection: Tunnel, select the same tunnel, configure required authentication, install it, and make a safe representative tool call.
Report observed evidence for each checkpoint and the exact error and next action for any blocker. Call setup complete only after the ChatGPT tool call succeeds.
```
The ChatGPT custom MCP plugin in this prompt is separate from the local Codex
plugin installed by `tunnel-client codex plugin install`.
## 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}`
- The `tunnel-client process started` log confirms process startup. Check
`/readyz` for readiness and `/health/control-plane` for observed polling.
Optional all-404 OAuth metadata discovery logs at INFO and reports
`not_advertised` in `/health/oauth`, including HTML or JSON 404 bodies.
See [startup supervision](docs/health.md#supervising-startup).
- 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
and registers discovered Harpoon targets. Timeouts, HTTP `429`/`5xx`, and
malformed successful metadata responses retry with bounded exponential
backoff until discovery succeeds or the process stops. Permanent errors
remain visible through readiness; discovery validation and trusted-origin
restrictions still apply.
- Before polling for Harpoon work, the runtime waits for startup discovery and
target registration to complete. Failed startup catalogs do not consume
commands, and readiness remains non-ready until registration succeeds.
Plain MCP servers without OAuth and explicitly scoped pollers
that exclude Harpoon remain supported. Transient HTTP `429`/`5xx` MCP startup
initialization errors also retry without replaying tunneled commands.
- After configured and startup OAuth-discovered Harpoon targets settle, it
emits one privacy-safe `harpoon startup catalog digest` INFO log. Compare
replicas only when they use the same tunnel ID and control-plane runtime API
key; the startup-only digest is a comparison aid, not convergence
enforcement.
- 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.
- OAuth discovery trusts the configured MCP origin by default. Before upgrading
deployments with separate metadata or authorization hosts, explicitly list
those origins with `--mcp.oauth-trusted-origin`, `MCP_OAUTH_TRUSTED_ORIGINS`, or
`mcp.oauth_trusted_origins`. See the [configuration reference](docs/configuration.md#mcp-server)
for trust boundaries and staged upgrade guidance. Full-client profile editing
also requires a [supported editor command](docs/profile-editor.md).
- Forwarding OAuth requests to a separate HTTPS origin requires an independent
opt-in: `--harpoon.oauth-forward-origin`, `HARPOON_OAUTH_FORWARD_ORIGINS`, or
`harpoon.oauth_forward_origins`. Discovery trust alone remains insufficient.
Approved discovered endpoints retain their OAuth roles and groups; other
origins remain subject to the existing registration policy. See
[OAuth forwarding origins](docs/configuration.md#oauth-forwarding-origins)
for exact-origin matching and deployment guidance.
- 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 supports a generic reverse-proxy path prefix. Prefix-stripping
proxies need no base-path setting; prefix-preserving proxies use
`--admin-ui.base-path`. An explicit `--admin-ui.public-origin` can allow the
browser's origin for guarded actions through a reverse proxy. See
[reverse proxy paths](docs/configuration.md#reverse-proxy-paths) for mount
URLs, security boundaries, and configuration examples.
- Local `GET /health?details=true`, `GET /health/mcp`, and `GET /health/oauth`
expose bounded observations of legacy initialize and modern `server/discover`
MCP discovery, OAuth startup probes, polling, response delivery, queues, and
active work. Plain `/health` stays compact unless `--health.show-details=true`
is set (default false). See the [health reference](docs/health.md) for examples,
Unix sockets, and the difference between readiness and observed discovery.
- 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.
### Harpoon target templates
Opt-in Harpoon templates let callers provide bounded identifiers for an
operator-configured GET, POST, or PUT operation, such as `/cases/{case_id}` or
`/profiles?session-id={session_id}`. The client fixes the destination, method,
query names, and authentication headers, validates each identifier, and never
follows redirects. POST/PUT require an explicit body policy for content types,
byte limits, required or optional bodies, and validation. GET remains bodyless;
DELETE is unsupported. Existing exact-URL targets continue to work.
Templates use HTTPS by default. An operator can set `allow_loopback_http: true`
on one template to call a literal loopback IP with a fixed port over HTTP.
Those calls bypass configured HTTP proxies so local API credentials stay on
the local connection. The setting does not enable other plaintext targets.
Templates use YAML `config_version: 2` and `template.version: 1`, and execute
through the shared `call_target` MCP tool without a caller-supplied method.
Exact targets keep their required method argument. `list_targets` publishes
each template's complete invocation schema, public parameter descriptions, and
validated examples when available. Writes require the advertised `operation`
constant and never automatically replay after an ambiguous failure. Upgrade all
eligible clients before enabling writes or adding parameter metadata. See the
[target template guide](docs/harpoon-target-templates.md) for complete
configuration, discovery and invocation examples, authorization requirements,
limits, and upgrade behavior.
## 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:
```bash
./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` is the supported queue setting. Ordinary public
builds use the Go in-memory backend; `rust` requires a binary with the
optional linked Rust adapter. Rust Redis support has been removed. The
deprecated `--engine-redis-url` flag, nonempty `TUNNEL_ENGINE_REDIS_URL`, or an
explicit Redis backend selection returns a removal error before startup.
Remove retired settings and use `inmem` only for local, ephemeral work, or
keep the prior version for Redis-backed setups.
- `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.
- The first control-plane poll attempt requests the shorter of
`--control-plane.initial-poll-timeout` (default `30s`) and the configured
wait, while retaining its normal client deadline. Both wait settings default
to `30s`. A lower initial-poll timeout can shorten the first requested wait.
Subsequent polls use `--control-plane.poll-timeout` /
`CONTROL_PLANE_POLL_TIMEOUT`, including after an initial failure.
If an HTTP-proxied poll loses its connection
before response headers with an EOF-style error while neither deadline has
fired, tunnel-client automatically learns a shorter
process-local timeout for future polls. The learned timeout only decreases,
never below 5 seconds, while the configured poll timeout remains its ceiling.
Subsequent direct and Unix-socket polls keep the configured timeout.
- `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](LICENSE).