browser-use

---
name: browser-use
description: Control a real browser to navigate pages, click, type, fill forms, inspect rendered UI, take screenshots, or record video. Load only when the user asks to open or automate a browser, interact with or test rendered page UI, scrape a site that needs browser execution, or capture a browser screenshot or video. Do not load for backend logs, traces, API or stream events, source-code inspection, or plain HTTP or web research that does not require a browser.
---

# Browser Use with CDP

Drive the browser through its native Chrome DevTools Protocol over the
remote-debugging WebSocket. This works with zero dependencies: launch the
browser with `--remote-debugging-port`, then talk JSON over `fetch` and the
built-in `WebSocket` global (available in Bun and Node ≥ 22 — no `ws` package).

If the project already has Playwright or Puppeteer installed, using it is
usually simpler — reach for raw CDP when no automation library is available,
when protocol-level control is needed, or when recording a deterministic
visual demo.

Protocol reference: https://chromedevtools.github.io/devtools-protocol/.
The running browser's exact schema is at `http://127.0.0.1:<port>/json/protocol`;
tip-of-tree docs can differ from the installed version.

## Visible by default when a display exists

When the computer has a display, prefer a visible (headful) browser for any
task the user might watch or take over: clicking or typing, forms, sign-in,
checkout/payment, CAPTCHAs or bot protection, and user handoff. Most browser
tasks exist because plain HTTP is not enough; a headless browser is more
likely to trigger bot protection and gives the user no way to observe or step
in. Visible does not mean pixel-driven: keep operating the page over CDP, and
the user sees every action in the window.

Use headless mode only for work the user explicitly wants in the background
and that cannot require interaction or handoff, such as read-only scraping,
CI, or screenshot/PDF generation, or when no display exists. A headless page
does not satisfy a request to open or reopen a site in a browser the user can
see.

When the user asks to review, watch, or take over, leave that browser window
open after the task. Do not kill or close it before replying.

## Workflow

1. Find a Chromium-based browser (below). If none exists, see "No Chrome installed".
2. Launch with a dedicated profile and remote debugging. Never attach to the
   user's normal profile unless explicitly asked.
3. Discover targets via `/json/list`; pick the `"page"` target by URL or title.
4. Connect to its `webSocketDebuggerUrl` and enable only the domains you need
   (usually `Page`, `Runtime`, `DOM`, `Input`; add `Network`, `Log` when debugging).
5. Inspect before acting: find elements by accessible name, label, text, role,
   stable ID, or placeholder — not generated classes or child indexes.
6. Act through `Input.*` for user-like interactions; use `Runtime.evaluate` for
   inspection, coordinate math, and setup with no meaningful user interaction.
7. Wait on observable state, never fixed sleeps alone.
8. Verify the result (DOM state, URL, screenshot, console/network events).
9. Clean up temporary background work: stop screencasts and close the
   WebSocket. Kill a browser you launched only when the user did not ask to
   review, watch, or take over the visible window.

## Finding the browser

Any Chromium-based browser supports CDP (Chrome, Chromium, Edge, Brave). Probe
in order:

```bash
# macOS
for c in "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" \
         "/Applications/Chromium.app/Contents/MacOS/Chromium" \
         "/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge" \
         "/Applications/Brave Browser.app/Contents/MacOS/Brave Browser"; do
  [ -x "$c" ] && { echo "$c"; break; }
done

# Linux
for c in google-chrome google-chrome-stable chromium chromium-browser microsoft-edge brave-browser; do
  command -v "$c" && break
done
```

On Windows, check `%ProgramFiles%\Google\Chrome\Application\chrome.exe`,
`%ProgramFiles(x86)%\...`, `%LocalAppData%\Google\Chrome\Application\chrome.exe`,
and the same patterns for `Microsoft\Edge`.

### No Chrome installed

Any browser found by the probe above works identically — use it. If truly no
Chromium-based browser exists, do not install or download one automatically.
Tell the user that browser use requires Chrome or another Chromium-based
browser and recommend either:

1. Install Chrome on the current computer, then retry the browser task.
2. Teleport the conversation back to its Cloud sandbox, where a
   browser is already installed.

Wait for the user to choose. Do not silently replace the browser task with
plain HTTP or claim browser automation succeeded.

## Launching

Use a disposable profile and a fixed port. Chrome refuses to run as root
without `--no-sandbox`, so add that flag when `id -u` is 0:

```bash
chrome_args=( \
  --remote-debugging-port=9222 \
  --user-data-dir=/tmp/cdp-profile \
  --window-size=1440,900 \
  --force-device-scale-factor=1 \
  --no-first-run \
  --no-default-browser-check \
)
[ "$(id -u)" -eq 0 ] && chrome_args+=(--no-sandbox)
"$CHROME" "${chrome_args[@]}" https://example.com
```

Add `--headless=new` only for explicitly invisible work or when no display
exists (see "Visible by default" above).
With `--remote-debugging-port=0`, read the chosen port from
`<user-data-dir>/DevToolsActivePort`. Launch in the background and poll
`http://127.0.0.1:9222/json/version` until it responds.

HTTP endpoints: `/json/version` (browser metadata + browser-level WebSocket URL),
`/json/list` (targets), `PUT /json/new?<url>` (open tab),
`/json/activate/<id>`, `/json/close/<id>`, `/json/protocol` (schema).

Attach to the **page** target for `Page`/`DOM`/`Runtime`/`Input` work; use the
**browser** target only for browser-wide commands (target control, downloads,
browser contexts).

## Minimal CDP client

CDP messages are JSON with monotonically increasing request ids. Run with `bun`:

```ts
const targets = await (await fetch("http://127.0.0.1:9222/json/list")).json();
const target = targets.find((t: any) => t.type === "page");
if (!target) throw new Error("No page target");

const ws = new WebSocket(target.webSocketDebuggerUrl);
await new Promise((resolve, reject) => {
  ws.onopen = resolve;
  ws.onerror = reject;
});

let nextId = 0;
const pending = new Map();
ws.onmessage = (event) => {
  const msg = JSON.parse(String(event.data));
  if (!msg.id) return handleEvent(msg); // Page.loadEventFired, Log.entryAdded, ...
  const p = pending.get(msg.id);
  if (!p) return;
  pending.delete(msg.id);
  msg.error ? p.reject(new Error(JSON.stringify(msg.error))) : p.resolve(msg.result);
};
ws.onclose = () => {
  for (const p of pending.values()) p.reject(new Error("socket closed"));
  pending.clear();
};

function send(method: string, params: object = {}): Promise<any> {
  return new Promise((resolve, reject) => {
    const id = ++nextId;
    pending.set(id, { resolve, reject });
    ws.send(JSON.stringify({ id, method, params }));
  });
}

await send("Page.enable");
await send("Runtime.enable");
```

Navigations destroy execution contexts and can invalidate in-flight
`Runtime.evaluate` calls; retry after observing the new document.

## Inspecting the page

Start with a concise UI inventory:

```ts
const result = await send("Runtime.evaluate", {
  expression: `JSON.stringify({
    buttons: [...document.querySelectorAll('button')].map((el) => ({
      text: el.innerText.trim(), aria: el.getAttribute('aria-label'), title: el.title
    })).filter((x) => x.text || x.aria || x.title),
    inputs: [...document.querySelectorAll('input, textarea, [contenteditable=true]')].map((el) => ({
      tag: el.tagName, type: el.type, placeholder: el.placeholder,
      aria: el.getAttribute('aria-label'), value: el.value
    }))
  })`,
  returnByValue: true,
});
```

Use `awaitPromise: true` for async expressions and `userGesture: true` when the
page requires user activation. Treat `exceptionDetails` in the result as an
error even though the CDP command itself succeeded.

`document.querySelector` does not cross shadow boundaries — traverse open
shadow roots explicitly; for closed shadow roots or remote-object work use the
`DOM` domain (`DOM.getDocument`, `DOM.querySelector`, `DOM.getBoxModel`).

## Clicking and typing

Compute coordinates in CSS pixels immediately before acting, then send native
input events:

```ts
async function point(expr: string) {
  const r = await send("Runtime.evaluate", {
    expression: `(() => {
      const el = ${expr};
      if (!el) return null;
      el.scrollIntoView({ block: 'center', inline: 'center' });
      const b = el.getBoundingClientRect();
      return { x: b.left + b.width / 2, y: b.top + b.height / 2 };
    })()`,
    returnByValue: true,
  });
  if (!r.result.value) throw new Error(`Element not found: ${expr}`);
  return r.result.value;
}

async function click(expr: string) {
  const { x, y } = await point(expr);
  await send("Input.dispatchMouseEvent", { type: "mouseMoved", x, y });
  await send("Input.dispatchMouseEvent", { type: "mousePressed", x, y, button: "left", buttons: 1, clickCount: 1 });
  await send("Input.dispatchMouseEvent", { type: "mouseReleased", x, y, button: "left", buttons: 0, clickCount: 1 });
}
```

Focus an editable element (click it), then insert text:

```ts
await click(`document.querySelector('input[aria-label="Search"]')`);
await send("Input.insertText", { text: "search terms" });
```

Use `Input.insertText` for text and Unicode; use paired `Input.dispatchKeyEvent`
(`keyDown` + `keyUp` with `key`, `code`, `windowsVirtualKeyCode`) for Enter,
Escape, arrows, Tab, and shortcuts. Modifier bits: Alt=1, Ctrl=2, Meta=4, Shift=8.

Native `<select>` and framework-controlled inputs may need the prototype setter
plus bubbling events:

```ts
const setter = Object.getOwnPropertyDescriptor(HTMLInputElement.prototype, "value").set;
setter.call(input, "new value");
input.dispatchEvent(new Event("input", { bubbles: true }));
input.dispatchEvent(new Event("change", { bubbles: true }));
```

Prefer real `Input.*` events for the behavior being demonstrated or tested;
direct DOM mutation is fine for deterministic setup and inspection.

## Waiting reliably

A returned command does not mean the action completed. Poll the state that
proves completion:

```ts
async function waitFor(expr: string, timeoutMs = 30_000) {
  const start = Date.now();
  while (Date.now() - start < timeoutMs) {
    const r = await send("Runtime.evaluate", { expression: `Boolean(${expr})`, returnByValue: true });
    if (r.result.value) return;
    await new Promise((res) => setTimeout(res, 250));
  }
  throw new Error(`Timed out waiting for ${expr}`);
}

await waitFor(`document.body.innerText.includes('Saved')`);
```

For navigation, wait on `Page.loadEventFired` or a lifecycle `networkIdle`
event — but SPA route changes may emit neither, so prefer the UI condition
that actually matters.

## Screenshots, PDF, and video

```ts
const shot = await send("Page.captureScreenshot", { format: "png" });
await Bun.write("screenshot.png", Buffer.from(shot.data, "base64"));
```

`captureBeyondViewport: true` for full-page; `Page.getLayoutMetrics` + `clip`
for exact regions; `Page.printToPDF` for PDFs. For video recording with
`Page.startScreencast` and demo-polish tips, read
[references/recording.md](references/recording.md).

## Debugging failures

Enable `Network` and `Log`, then watch `Network.requestWillBeSent`,
`Network.responseReceived`, `Network.loadingFailed`, `Runtime.consoleAPICalled`,
`Runtime.exceptionThrown`, and `Log.entryAdded`. Fetch bodies with
`Network.getResponseBody`. Never log authorization headers, cookies, API keys,
passwords, or response bodies containing secrets — scrub before returning
output to context.

Common failure modes:

- **ECONNREFUSED on the port**: browser exited, wrong port, or debugging not
  enabled — check `/json/version` first.
- **No matching target**: inspect `/json/list`; match by URL/title, don't take
  the first page blindly.
- **Execution context destroyed**: the page navigated; wait for the new
  document and re-evaluate.
- **Click misses an existing element**: scroll into view and recalculate the
  box immediately before dispatching.
- **Typed text doesn't stick in a controlled input**: focus + `Input.insertText`,
  or the prototype-setter pattern above.
- **Opening DevTools disconnects automation**: embedded DevTools can detach
  other clients — don't open DevTools during a run.
- **Page commands fail on the browser endpoint**: attach to the page target.

## Safety

Browser automation acts with the user's browser authority.

- Use a disposable profile by default.
- Do not submit purchases, publish content, send messages, delete data, or
  accept consequential dialogs without explicit authorization.
- Do not extract saved passwords, tokens, cookies, or unrelated browsing data.
- Stay within the requested origin and workflow.
- Keep the remote-debugging listener on loopback (`127.0.0.1`) unless the user
  explicitly needs remote access and has authentication in place.

From letta-ai/letta-code at c1033d9, shown as plain text under its license: Apache-2.0 (permissive). The license text is in LICENSE.

• SKILL.md13 KB · 3c98f7be0b95
• references/
• recording.md2.0 KB · 976bac75e66d

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