---
title: Test on an Existing Browser
description: Attach to a browser you already have open — with your tabs, state, and extensions — instead of launching a fresh one.
---

# Test on an Existing Browser

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If you need to control a browser that's already open — with specific tabs, complex state, or extensions you've configured manually — you can attach to it instead of launching a new one.

::: tip Simpler alternative
For most cases, a [persistent Chrome profile](/local/browser-automation/persistent-profile) is simpler and doesn't require any setup. Use the relay approach below only when you need to interact with a browser that's already running.
:::

This uses the **Shiplight Chrome Extension** as a relay between your agent and your browser. See [Attach to Existing Browser](/mcp/attach-to-browser) for setup — you'll need to install the extension and enable the relay server. A direct CDP connection (no extension) is also supported.

```
Attach to my browser and check if the payment form
on the current page has any console errors.
```

Your agent auto-discovers tabs via the extension relay — no URL or configuration needed.