# What is a headless browser?

A headless browser is a real web browser run without a window, controlled by code, for tests, scraping, screenshots and AI agents.

**On Runtime each headless browser gets a Linux microVM of its own, so
parallel runs never share cookies, a profile or a kernel, and it bills only the
CPU it uses.** Playwright's Chromium installs in two commands on the stock
Ubuntu 24.04 image ([the sandbox environment](/docs/sandbox-environment)).

## Headless and headed

Chrome's documentation puts it plainly: "With Chrome Headless mode, you can
run the browser in an unattended environment, without any visible UI." Since
Chrome 112 headless and headed Chrome share one implementation; the older
separate build lives on as `chrome-headless-shell`. Playwright runs tests
headless by default (`--headed` shows the window) and uses that lighter shell
for headless Chromium unless you opt into the full browser with the
`chromium` channel.

| Mode                              | What it is                             | On Runtime                                                                              |
| --------------------------------- | -------------------------------------- | --------------------------------------------------------------------------------------- |
| Headless shell                    | Lightweight Chromium build, no display | Playwright's default headless Chromium, via `exec`                                      |
| New headless (`chromium` channel) | Full Chrome with no window             | The same install, `channel: "chromium"`                                                 |
| Headed                            | A visible browser on a desktop         | The sandbox [desktop](/docs/javascript#a-desktop) with Firefox, live view and recording |

## Why AI agents use one

An agent that reads documentation, checks a deployed app or fills a form needs
a browser that code can drive and that renders JavaScript. Running it on your
own server hands untrusted pages your network; running it in a sandbox keeps
those pages behind the sandbox's egress rules, with private and internal
addresses always refused.

Agents that plan from pixels use a headed desktop and
[computer use](/glossary/computer-use). Agents that act through the page's
structure, clicking selectors and reading text, are faster and cheaper with a
headless browser.

## Run one

```bash no-run
sudo npx playwright install-deps chromium
npx playwright install chromium
```

```ts check
import { Sandbox } from "withruntime";

const script = `
const { chromium } = require("playwright");
(async () => {
  const browser = await chromium.launch({ headless: true });
  const page = await browser.newPage();
  await page.goto("https://example.com");
  console.log(await page.title());
  await browser.close();
})();
`;

await using sbx = await Sandbox.create({ diskMiB: 8192 });
const slow = { check: true, timeoutMs: 600_000 } as const;
await sbx.exec("npm install --no-fund --no-audit playwright", slow);
await sbx.exec("sudo npx playwright install-deps chromium", slow);
await sbx.exec("npx playwright install chromium", slow);
await sbx.files.write("/workspace/title.cjs", script);
console.log((await sbx.exec(["node", "title.cjs"], { check: true })).stdout);
```

Ask for 8 GiB of disk: Chromium and its libraries take a large share of the
default 4 GiB. Put the install in a [custom image](/docs/images) and later
sandboxes start with the browser ready.

## Related

- [How to run Playwright in a cloud sandbox](/integrations/playwright)
- [How to run a browser automation agent](/use-cases/browser-automation-agent)
- [What is computer use?](/glossary/computer-use)
- [What is egress control?](/glossary/egress-control)

## Sources

- [Chrome for Developers, Chrome Headless mode](https://developer.chrome.com/docs/chromium/headless), checked 25 September 2026
- [Playwright, Browsers](https://playwright.dev/docs/browsers), checked 25 September 2026
- [Playwright, Command line](https://playwright.dev/docs/test-cli), checked 25 September 2026

Facts on this page were checked on 25 September 2026.