Attach Chrome

Use this guide when:

  • Chrome already exists outside PinchTab
  • you want the PinchTab server to register that browser as an instance
  • you already have a browser-level DevTools WebSocket URL

Do not use this guide if your goal is simply:

  • start a browser for your agent
  • run the normal local PinchTab workflow

For that, use managed instances with pinchtab and POST /instances/start.

Launch vs attach

The mental model is:

launch = PinchTab starts and owns the browser
attach = PinchTab registers an already running browser

With attach:

  • Chrome is started somewhere else
  • PinchTab receives a cdpUrl
  • the server registers that browser as an attached instance

What is implemented today

The current codebase implements:

  • POST /instances/attach — starts a child pinchtab bridge --cdp-attach ... process that wraps the external browser. The bridge speaks the normal PinchTab HTTP API; the orchestrator registers the bridge’s HTTP URL (not the raw ws:// CDP URL) as the routable instance URL.
  • POST /instances/attach-bridge — registers an already-running PinchTab bridge as an instance (unchanged).
  • attach policy in config under security.attach
  • attached-instance metadata in GET /instances

The attach request body is:

{
  "name": "shared-chrome",
  "cdpUrl": "ws://127.0.0.1:9222/devtools/browser/...",
  "provider": "chrome",
  "browser": "chrome-local"
}

browser is optional and accepts a provider name (chrome, cloak) or a configured target name from browser.targets. When browser.targets is configured, an omitted value attaches to the configured default target and the target’s browser is used. If you also pass provider, it must agree with the browser value. Without browser targets, provider defaults to chrome; use cloak for a CloakBrowser endpoint (equivalent to --browser cloak on the CLI).

Accepted cdpUrl shapes:

  • browser-level WebSocket URL: ws://host:port/devtools/browser/<id>
  • HTTP DevTools origin: http://host:port (resolved through /json/version)
  • HTTP /json/version URL

Page-level URLs (/devtools/page/...) are rejected.

There is currently no CLI attach command.

Step 1: enable attach policy

Attach is disabled unless you allow it in config.

Example:

{
  "security": {
    "attach": {
      "enabled": true,
      "allowHosts": ["127.0.0.1", "localhost", "::1"],
      "allowSchemes": ["ws", "wss"],
      "forwardProxyAuth": false
    }
  }
}

What this does:

  • enables the attach endpoint
  • restricts which hosts are accepted
  • restricts which URL schemes are accepted

What this does not do:

  • it does not start Chrome
  • it does not define a global remote browser
  • it does not replace managed instances

Step 2: start Chrome with remote debugging

Example:

terminal 
google-chrome --remote-debugging-port=9222# Or on some systems:# chromium --remote-debugging-port=9222
google-chrome --remote-debugging-port=9222# Or on some systems:# chromium --remote-debugging-port=9222

This makes Chrome expose a browser-level DevTools endpoint.

Step 3: get the browser WebSocket URL

Query Chrome:

terminal 
curl -s http://127.0.0.1:9222/json/version | jq .
curl -s http://127.0.0.1:9222/json/version | jq .
Response 
{
  "webSocketDebuggerUrl": "ws://127.0.0.1:9222/devtools/browser/abc123"
}

The value of webSocketDebuggerUrl is the cdpUrl you pass to PinchTab.

Step 4: attach it to PinchTab

terminal 
curl -X POST http://localhost:9867/instances/attach \  -H "Content-Type: application/json" \  -d '{    "name": "shared-chrome",    "cdpUrl": "ws://127.0.0.1:9222/devtools/browser/abc123",    "browser": "chrome-local"  }'
curl -X POST http://localhost:9867/instances/attach \  -H "Content-Type: application/json" \  -d '{    "name": "shared-chrome",    "cdpUrl": "ws://127.0.0.1:9222/devtools/browser/abc123",    "browser": "chrome-local"  }'
Response 
{
  "id": "inst_0a89a5bb",
  "profileId": "prof_278be873",
  "profileName": "shared-chrome",
  "port": "",
  "mode": "headed",
  "headless": false,
  "status": "running",
  "attached": true,
  "cdpUrl": "ws://127.0.0.1:9222/devtools/browser/abc123",
  "browser": "chrome"
}

Notes:

  • name is optional; if omitted, the server generates one like attached-...
  • the server validates the URL against security.attach.allowHosts and security.attach.allowSchemes

Step 5: confirm it is registered

terminal 
pinchtab instances
curl -s http://localhost:9867/instances | jq .

An attached instance appears in the normal instance list with:

  • attached: true
  • cdpUrl: ...
  • status: "running"

Ownership and lifecycle

Attached instances are externally owned, but PinchTab still owns a bridge wrapper around them.

That means:

  • PinchTab did not launch the browser
  • PinchTab spawned a child pinchtab bridge --cdp-attach ... process that wraps the external CDP endpoint and serves normal PinchTab routes
  • the external Chrome/CloakBrowser process remains outside PinchTab lifecycle ownership

In practical terms:

  • POST /instances/{id}/stop shuts down the child PinchTab bridge — the external Chrome process is left running
  • routes like /tabs, /snapshot, /action, /screenshot go to the child bridge, which talks CDP to the external browser through a chromedp.NewRemoteAllocator

When attach makes sense

Use attach when:

  • Chrome is managed by another system
  • Chrome is already running in a separate service or container
  • you want the server to know about an externally managed browser
  • you want to keep browser ownership outside PinchTab

Security

Attach widens the trust boundary, so keep it locked down.

Recommended rules:

  • leave attach disabled unless you need it
  • keep allowHosts narrow
  • keep allowSchemes narrow
  • leave forwardProxyAuth disabled unless the attached browser process and CDP transport are trusted
  • set PINCHTAB_TOKEN when the server is reachable outside localhost
  • only attach to CDP endpoints you trust

If you set allowHosts to ["*"], PinchTab accepts any reachable attach host with an allowed scheme. That is a documented, non-default, security-reducing override: it removes host allowlisting entirely and should only be used on isolated, operator-controlled networks.

Also remember:

  • Chrome DevTools gives powerful browser control
  • a reachable CDP endpoint should be treated as sensitive infrastructure

If Chrome is remote, prefer a tunnel rather than exposing the debugging port broadly.

Operational model

The intended model is:

agent -> PinchTab server -> attached external Chrome

This is an expert path, not the default user path.

The default path remains:

terminal 
pinchtab
pinchtab

then managed instance start via:

terminal 
pinchtab instance start
curl -X POST http://localhost:9867/instances/start \  -H "Content-Type: application/json" \  -d '{"mode":"headless"}'
  • cloakbrowser.md — full CloakBrowser configuration and the --browser cloak attach variant
  • docker.md — running PinchTab (and the local CloakBrowser smoke image) in containers
  • headed-mode.md — manual headed setup outside the bundled image
  • security.md — attach policy details, IDPI, token handling