---
summary: "Chrome extension: let gensparx drive your existing Chrome tab"
read_when:
  - You want the agent to drive an existing Chrome tab (toolbar button)
  - You need remote Gateway + local browser automation via Tailscale
  - You want to understand the security implications of browser takeover
title: "Chrome Extension"
---

# Chrome extension (browser relay)

The gensparx Chrome extension lets the agent control your **existing Chrome tabs** (your normal Chrome window) instead of launching a separate gensparx-managed Chrome profile.

Attach/detach happens via a **single Chrome toolbar button**.

## What it is (concept)

There are three parts:

- **Browser control service** (Gateway or node): the API the agent/tool calls (via the Gateway)
- **Local relay server** (loopback CDP): bridges between the control server and the extension (`http://127.0.0.1:18792` by default)
- **Chrome MV3 extension**: attaches to the active tab using `chrome.debugger` and pipes CDP messages to the relay

gensparx then controls the attached tab through the normal `browser` tool surface (selecting the right profile).

## Install / load (unpacked)

1. Install the extension to a stable local path:

```bash
gensparx browser extension install
```

2. Print the installed extension directory path:

```bash
gensparx browser extension path
```

3. Chrome → `chrome://extensions`

- Enable “Developer mode”
- “Load unpacked” → select the directory printed above

4. Pin the extension.

## Updates (no build step)

The extension ships inside the gensparx release (npm package) as static files. There is no separate “build” step.

After upgrading Gensparx:

- Re-run `gensparx browser extension install` to refresh the installed files under your gensparx state directory.
- Chrome → `chrome://extensions` → click “Reload” on the extension.

## Use it (set gateway token once)

gensparx ships with a built-in browser profile named `chrome` that targets the extension relay on the default port.

Before first attach, open extension Options and set:

- `Port` (default `18792`)
- `Gateway token` (must match `gateway.auth.token` / `GENSPARX_GATEWAY_TOKEN`)

Use it:

- CLI: `gensparx browser --browser-profile chrome tabs`
- Agent tool: `browser` with `profile="chrome"`

If you want a different name or a different relay port, create your own profile:

```bash
gensparx browser create-profile \
  --name my-chrome \
  --driver extension \
  --cdp-url http://127.0.0.1:18792 \
  --color "#00AA00"
```

### Custom Gateway ports

If you're using a custom gateway port, the extension relay port is automatically derived:

**Extension Relay Port = Gateway Port + 3**

Example: if `gateway.port: 19001`, then:

- Extension relay port: `19004` (gateway + 3)

Configure the extension to use the derived relay port in the extension Options page.

## Attach / detach (toolbar button)

- Open the tab you want gensparx to control.
- Click the extension icon.
  - Badge shows `ON` when attached.
- Click again to detach.

## Which tab does it control?

- It does **not** automatically control “whatever tab you’re looking at”.
- It controls **only the tab(s) you explicitly attached** by clicking the toolbar button.
- To switch: open the other tab and click the extension icon there.

## Badge + common errors

- `ON`: attached; gensparx can drive that tab.
- `…`: connecting to the local relay.
- `!`: relay not reachable/authenticated (most common: relay server not running, or gateway token missing/wrong).

If you see `!`:

- Make sure the Gateway is running locally (default setup), or run a node host on this machine if the Gateway runs elsewhere.
- Open the extension Options page; it validates relay reachability + gateway-token auth.

## Remote Gateway (use a node host)

### Local Gateway (same machine as Chrome) — usually **no extra steps**

If the Gateway runs on the same machine as Chrome, it starts the browser control service on loopback
and auto-starts the relay server. The extension talks to the local relay; the CLI/tool calls go to the Gateway.

### Remote Gateway (Gateway runs elsewhere) — **run a node host**

If your Gateway runs on another machine, start a node host on the machine that runs Chrome.
The Gateway will proxy browser actions to that node; the extension + relay stay local to the browser machine.

If multiple nodes are connected, pin one with `gateway.nodes.browser.node` or set `gateway.nodes.browser.mode`.

## Sandboxing (tool containers)

If your agent session is sandboxed (`agents.defaults.sandbox.mode != "off"`), the `browser` tool can be restricted:

- By default, sandboxed sessions often target the **sandbox browser** (`target="sandbox"`), not your host Chrome.
- Chrome extension relay takeover requires controlling the **host** browser control server.

Options:

- Easiest: use the extension from a **non-sandboxed** session/agent.
- Or allow host browser control for sandboxed sessions:

```json5
{
  agents: {
    defaults: {
      sandbox: {
        browser: {
          allowHostControl: true,
        },
      },
    },
  },
}
```

Then ensure the tool isn’t denied by tool policy, and (if needed) call `browser` with `target="host"`.

Debugging: `gensparx sandbox explain`

## Remote access tips

- Keep the Gateway and node host on the same tailnet; avoid exposing relay ports to LAN or public Internet.
- Pair nodes intentionally; disable browser proxy routing if you don’t want remote control (`gateway.nodes.browser.mode="off"`).

## How “extension path” works

`gensparx browser extension path` prints the **installed** on-disk directory containing the extension files.

The CLI intentionally does **not** print a `node_modules` path. Always run `gensparx browser extension install` first to copy the extension to a stable location under your gensparx state directory.

If you move or delete that install directory, Chrome will mark the extension as broken until you reload it from a valid path.

## Security implications (read this)

This is powerful and risky. Treat it like giving the model “hands on your browser”.

- The extension uses Chrome’s debugger API (`chrome.debugger`). When attached, the model can:
  - click/type/navigate in that tab
  - read page content
  - access whatever the tab’s logged-in session can access
- **This is not isolated** like the dedicated gensparx-managed profile.
  - If you attach to your daily-driver profile/tab, you’re granting access to that account state.

Recommendations:

- Prefer a dedicated Chrome profile (separate from your personal browsing) for extension relay usage.
- Keep the Gateway and any node hosts tailnet-only; rely on Gateway auth + node pairing.
- Avoid exposing relay ports over LAN (`0.0.0.0`) and avoid Funnel (public).
- The relay blocks non-extension origins and requires gateway-token auth for both `/cdp` and `/extension`.

Related:

- Browser tool overview: [Browser](/tools/browser)
- Security audit: [Security](/gateway/security)
- Tailscale setup: [Tailscale](/gateway/tailscale)
