Built-in browser
A browser in the side panel that the agent can drive, to open and try the app you are working on.
Kettu has a browser in the side panel. The agent can open the app it is working on, look at it and click through it while you watch, and you can use it yourself.
Opening it
Click Browser in the top bar. Each session has its own page. Type in the address field: a bare address gets https://, a local one such as localhost:3000 gets http://. The header has Back, Forward, Reload, Open in browser, which opens the page in your default browser, and Maximize.
When the agent opens a page and the side panel shows nothing else, the browser opens by itself. If another pane is showing, the Browser button gets a dot instead.
What the agent can do
The browser’s tools come with Kettu’s built-in MCP server. With them the agent can:
- open an address, go back and reload
- read an outline of the page and take screenshots
- click, type, press keys, scroll and choose options
- wait for text to appear
- read console messages and network requests, and run JavaScript in the page
While it works, a bar says Claude Code is using the browser, with the session’s agent named, and Stop. Stop, or typing or clicking in the page yourself, gives you control. The bar then says You have control, and the agent’s browser steps fail until you click Hand back.
Which agents can use it
Claude Code and Codex get the browser tools. Other agents get them when they accept MCP servers over HTTP; for those that do not, Settings › MCP servers says so. To leave Kettu’s tools out of one agent’s sessions, turn off its switch there, such as Kettu’s tools in Codex. This removes all of Kettu’s tools for that agent, not only the browser, from the agent’s next start.
Sites the agent opens
The agent opens a local dev server without asking: localhost, 127.0.0.1, [::1], and names ending in .localhost or .test. Any other site asks you first, in the conversation and in the browser pane:
| Answer | Effect |
|---|---|
| Allow for this session | This session’s page may open the site |
| Always for this project | Every session in the project may open it, from now on |
| Deny | The agent’s step fails |
A request left unanswered for 2 minutes ends as Not answered in time. While it waits, it notifies you as a permission request when Kettu is not in front; see Notifications. Settings › Browser › Always allowed sites lists the sites each project allows, with Remove.
Sign-ins and site data
Every session shares one browser profile, kept between launches, so you sign in to a site once. Settings › Browser › Clear browsing data removes cookies, site storage and cache, which signs you out of every site.
What the browser does not do
It opens only http and https pages, not local files. Downloads are blocked, with a button to open the page in your default browser instead, and pages are refused permissions such as the camera or microphone.