---
name: browser-harness
description: Direct browser control via CDP. Use when the user wants to automate, scrape, test, or interact with web pages. Connects to the user's already-running Chrome.
---

# browser-harness

For first-time install or reconnect/bootstrap, read `install.md` first. For normal use, stay in this file. **Read `helpers.py` first.** The code is the doc.

Available interaction skills:
- `cookies.md`
- `cross-origin-iframes.md`
- `dialogs.md`
- `downloads.md`
- `drag-and-drop.md`
- `dropdowns.md`
- `iframes.md`
- `network-requests.md`
- `print-as-pdf.md`
- `screenshots.md`
- `scrolling.md`
- `shadow-dom.md`
- `tabs.md`
- `uploads.md`
- `viewport.md`

Available domain skills:
- `tiktok/upload.md`

## Tool call shape

```bash
browser-harness <<'PY'
# any python. helpers pre-imported. daemon auto-starts.
PY
```

`run.py` calls `ensure_daemon()` before `exec` — you never start/stop manually unless you want to.

### Remote browsers

Remote is optional. Use it for parallel agents, sub-agents, or deployment.

If `BROWSER_USE_API_KEY` is already present in `.env` or the environment, start a remote daemon with:

Run this from the repo root:

```bash
uv run python - <<'PY'
from admin import start_remote_daemon
print(start_remote_daemon("work"))
PY
BU_NAME=work uv run browser-harness <<'PY'
print(page_info())
PY
```

Leaving a remote daemon running bills until the session timeout.

Parallel agents should use distinct `BU_NAME`s and can share the same `helpers.py`; shared improvements are expected, and changes should stay general enough that other agents benefit rather than break.

## Search first

After cloning the repo, search `interaction-skills/` for reusable UI mechanics and `domain-skills/` for site-specific workflows before inventing a new approach.

Useful commands:

```bash
rg --files interaction-skills domain-skills
rg -n "dropdown|iframe|upload|tiktok" interaction-skills domain-skills
```

## Post-task ritual (self-improving harness)

After every browser task, extract ONE generalizable friction point from the interaction (a failed selector strategy, a slow pattern, a missing helper, a confusing result) and make the **simplest possible** improvement:
- a 2-line helper in `helpers.py`, OR
- a one-line gotcha in this file, OR
- a correction to a wrong recipe here.

Commit with the task. The skill gets sharper every use. Skip only if nothing was surprising.

If you solve a specific website and learn a lot, create a PR to this repo with reusable learnings in `domain-skills/` or `interaction-skills/` — no secrets, no user data, no overfit recipes, just how the site works, what to wait for, and what patterns matter.

## What actually works

- **Scraping**: `js("...custom query...")`. Bespoke selectors beat generic DOM helpers.
- **Clicking**: `screenshot()` → look → `click(x, y)`. Passes through iframes/shadow/cross-origin at the compositor level.
- **Bulk HTTP**: `http_get(url)` + `ThreadPoolExecutor`. No browser for static pages (249 Netflix pages in 2.8s).
- **After goto**: `wait_for_load()`.
- **Wrong/stale tab**: `ensure_real_tab()`. Daemon also auto-recovers from stale sessions on next call.
- **Verification**: `ensure_real_tab(); print(page_info())` is the simplest "is this alive?" check.
- **Iframe sites** (Azure blades, Salesforce): `click(x, y)` passes through; for DOM use `js(expr, target_id=iframe_target("sandbox"))`. Iframe rects are iframe-local — add the host iframe's offset for page coords.
- **Auth wall**: redirected to login → stop and ask the user. Don't type credentials from screenshots.
- **Raw CDP** for anything helpers don't cover: `cdp("Domain.method", **params)`.

## Design constraints

- **Coordinate clicks default.** `Input.dispatchMouseEvent` goes through iframes/shadow/cross-origin at the compositor level.
- **Connect to the user's running Chrome.** Don't launch your own browser.
- **`cdp-use` is only for `CDPClient.send_raw`.** Prefer raw CDP strings over typed wrappers.
- **`run.py` stays tiny.** No argparse, subcommands, or extra control layer.
- **Helpers stay short.** Browser primitives in `helpers.py`; daemon/bootstrap and remote session admin live in `admin.py`.
- **Don't add a manager layer.** No retries framework, session manager, daemon supervisor, config system, or logging framework.

## Architecture

```text
Chrome / Browser Use cloud -> CDP WS -> daemon.py -> /tmp/bu-<NAME>.sock -> run.py
```

- Protocol is one JSON line each way.
- Requests are `{method, params, session_id}` for CDP or `{meta: ...}` for daemon control.
- Responses are `{result}` / `{error}` / `{events}` / `{session_id}`.
- `BU_NAME` namespaces socket, pid, and log files.
- `BU_CDP_WS` overrides local Chrome discovery for remote browsers.
- `BU_BROWSER_ID` + `BROWSER_USE_API_KEY` lets the daemon stop a Browser Use cloud browser on shutdown.

## Gotchas (field-tested)

- **Chrome 144+ `chrome://inspect/#remote-debugging` does NOT serve `/json/version`.** Read `DevToolsActivePort` instead.
- **Try attaching before asking for setup.** If `uv run browser-harness` already works, skip the remote-debugging instructions entirely.
- **The first connect may block on Chrome's Allow dialog.** If setup hangs, explicitly tell the user to click `Allow` in Chrome if it appears, then keep polling for up to 30 seconds instead of treating follow-on errors as a new failure.
- **`DevToolsActivePort` can exist before the port is actually listening.** Treat connection refused as "still enabling" and keep polling for up to 30 seconds.
- **Chrome may open the profile picker before any real tab exists.** If Chrome opens both a profile picker and the remote-debugging page, tell the user to choose their normal profile first, then tick the checkbox and click `Allow` if shown.
- **On macOS, if Chrome is already running, prefer AppleScript `open location` over `open -a ... URL`.** It reuses the current profile and avoids creating an extra startup path through the profile picker.
- **Omnibox popups are fake `page` targets.** Filter `chrome://omnibox-popup...` and other internals when you need a real tab.
- **CDP target order != Chrome's visible tab-strip order.** Use UI automation when the user means "the first/second tab I can see"; `Target.activateTarget` only shows a known target.
- **Default daemon sessions can go stale.** `ensure_real_tab()` re-attaches to a real page.
- **`no close frame received or sent` usually means a stale daemon / websocket.** Restart the daemon once with:
  `uv run python - <<'PY'`
  `from admin import restart_daemon`
  `restart_daemon()`
  `PY`
  before assuming setup is wrong.
- **Browser Use API is camelCase on the wire.** `cdpUrl`, `proxyCountryCode`, etc.
- **Remote `cdpUrl` is HTTPS, not ws.** Resolve the websocket URL via `/json/version`.
- **Stop cloud browsers with `PATCH /browsers/{id}` + `{\"action\":\"stop\"}`.**
- **React / controlled inputs ignore `el.value=...`.** Use the native setter to make React see the change:
  `Object.getOwnPropertyDescriptor(HTMLInputElement.prototype,'value').set.call(el,v); el.dispatchEvent(new Event('input',{bubbles:true}))`.
- **Radio/checkbox via React**: prefer `el.click()` over `el.checked=true` — React listens to the click event to drive state.
- **UI-library buttons (MUI Select, dropdown overlays)**: JS `.click()` on `[role=button]` often does NOT fire the library's handler. Screenshot → `click(x,y)` via CDP instead.
- **Keyboard listeners checking `e.key==='Enter'` on `keypress` or app-style form handlers**: use `dispatch_key(selector, 'Enter')`. Keep `press_key()` for raw browser-level key input like Tab, Escape, arrows, or when you want the real CDP path.
- **`alert()`/`confirm()` block the page thread.** Prefer `Page.handleJavaScriptDialog` plus `drain_events()`; see `interaction-skills/dialogs.md`.
- **Same-origin nested iframes** don't show up as CDP targets — walk `document.querySelector('iframe').contentDocument` (or `contentWindow`) recursively. Cross-origin iframes DO appear as targets; use `iframe_target("...")`.
- **Shadow DOM**: `document.querySelector` doesn't pierce shadow roots. Walk via `element.shadowRoot.querySelectorAll` (and recurse).
- **Submitting forms**: the "Submit" button isn't always the first `button[type=submit]` — on React Native Web etc. contact-method buttons share that type. Prefer the button whose text matches `/submit/i`, fall back to `form.requestSubmit()`.
- **Form success signals vary**: visible `#success-message`, captured `alert()` text, console log, or body text change. Check all sources — don't assume one convention.

## Interaction notes

- `interaction-skills/` holds reusable UI mechanics such as dialogs, tabs, dropdowns, iframes, and uploads.
- `domain-skills/` holds site-specific workflows and should be updated when you discover reusable patterns for a website.