---
title: browser - Browser
description: Control a browser to access and interact with web pages
---

Control a Chromium browser for web navigation, element interaction and content extraction. Supports JavaScript-rendered pages and uses a compact DOM snapshot so the Agent can efficiently understand page structure.

## Installation

<Tabs>
  <Tab title="CLI install (recommended)">
    ```bash
    cow install-browser
    ```

    This command will:
    - Install the `playwright` Python package (with auto-fallback for older systems)
    - Install system dependencies on Linux
    - Download the Chromium browser (Linux servers automatically use the headless build)
    - Detect China-mainland networks and use mirror acceleration
  </Tab>
  <Tab title="Manual install">
    ```bash
    pip install playwright
    playwright install chromium
    ```

    On Linux servers, install system dependencies as well:
    ```bash
    sudo playwright install-deps chromium
    ```

    On older systems (e.g. Ubuntu 18.04, glibc < 2.28), install a compatible version:
    ```bash
    pip install playwright==1.28.0
    python -m playwright install chromium
    ```

    To accelerate the Chromium download from China:
    ```bash
    export PLAYWRIGHT_DOWNLOAD_HOST=https://registry.npmmirror.com/-/binary/playwright
    python -m playwright install chromium
    ```
  </Tab>
</Tabs>

<Note>
  1. Supported on Ubuntu 20.04+, Debian 10+, macOS and Windows. Older systems such as Ubuntu 18.04 will fall back to a compatible version automatically.
  2. The browser tool has heavy dependencies (~300MB) and is optional. For lightweight web content retrieval, use the `web_fetch` tool.
</Note>

## Workflow

A typical browser workflow for the Agent:

1. **`navigate`** — Open the target URL
2. **`snapshot`** — Get a compact DOM with auto-numbered interactive elements (`ref`)
3. **`click` / `fill` / `select`** — Operate elements by `ref`
4. **`snapshot`** — Snapshot again to verify the result

## Supported Actions

| Action | Description | Key parameters |
| --- | --- | --- |
| `navigate` | Open URL | `url` |
| `snapshot` | Get structured page text (primary way) | `selector` (optional) |
| `click` | Click an element | `ref` or `selector` |
| `fill` | Fill text into an input | `ref` or `selector`, `text` |
| `select` | Select a dropdown option | `ref` or `selector`, `value` |
| `scroll` | Scroll the page | `direction` (up/down/left/right) |
| `screenshot` | Save a screenshot to the workspace | `full_page` |
| `wait` | Wait for an element or timeout | `selector`, `timeout` |
| `press` | Press a key (Enter, Tab, etc.) | `key` |
| `back` / `forward` | Browser back / forward | - |
| `get_text` | Get an element's text content | `selector` |
| `evaluate` | Run JavaScript | `script` |

## Use Cases

- Access a URL to retrieve dynamic page content
- Fill in forms and log in
- Operate web elements (click buttons, select options, etc.)
- Verify the result of a deployed web page
- Scrape content that requires JS rendering

## Run Mode

The browser picks a mode based on the runtime environment:

| Environment | Mode |
| --- | --- |
| macOS / Windows | Headed (browser window visible) |
| Linux desktop (with DISPLAY) | Headed |
| Linux server (no DISPLAY) | Headless |

You can override it in `config.json`:

```json
{
  "tools": {
    "browser": {
      "headless": true
    }
  }
}
```

## Persistent Login

**Log in to a target site once and the Agent can keep using it.** Two ways are supported:

### Option 1: Persistent mode (default)

Works out of the box. Login state is saved under `~/.cow/browser_profile`. No configuration needed.

To disable persistence and start with a clean environment every time:

```json
{
  "tools": {
    "browser": {
      "persistent": false
    }
  }
}
```

### Option 2: CDP mode (attach to real Chrome)

Have the Agent connect to a separately launched real Chrome (instead of the Chromium bundled with Playwright) for full browser fingerprints. Useful for sites with strict bot detection.

Launch Chrome with a debugging port and a dedicated user data directory:

<Tabs>
  <Tab title="macOS">
    ```bash
    "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" \
      --remote-debugging-port=9222 \
      --user-data-dir="$HOME/.cow/chrome-cdp"
    ```
  </Tab>
  <Tab title="Linux">
    ```bash
    google-chrome \
      --remote-debugging-port=9222 \
      --user-data-dir="$HOME/.cow/chrome-cdp"
    ```
  </Tab>
  <Tab title="Windows">
    ```powershell
    & "C:\Program Files\Google\Chrome\Application\chrome.exe" `
      --remote-debugging-port=9222 `
      --user-data-dir="$env:USERPROFILE\.cow\chrome-cdp"
    ```
  </Tab>
</Tabs>

Then point the Agent at the endpoint in `config.json`:

```json
{
  "tools": {
    "browser": {
      "cdp_endpoint": "http://localhost:9222"
    }
  }
}
```

<Note>
  Chrome 137+ requires `--remote-debugging-port` to be paired with a dedicated `--user-data-dir`. As a result, the CDP-launched Chrome **cannot directly reuse the login state of your daily Chrome**; you'll need to log in once inside this dedicated profile.
</Note>