Browser Harness

browser-harness

Direct browser control via CDP. For task-specific edits, use agent-workspace/agent_helpers.py. For setup, install, or connection problems, read https://github.com/browser-use/browser-harness/blob/main/install.md.

When Not to Use

A basic fetch of public information needs no browser. If a plain HTTP request can read it — a public page, an API, docs — use curl or your fetch tool, and leave the browser alone. Use browser-harness when the task needs interaction (click, type, navigate), the user's logged-in session, JS rendering, or a bot-protected page. If a direct fetch fails or returns a shell page, then escalate to the browser.

Domain skills are off by default. Set BH_DOMAIN_SKILLS=1 to enable them; see the bottom section.

If BH_DOMAIN_SKILLS=1 and the task is site-specific, read every file in the matching $BH_AGENT_WORKSPACE/domain-skills/<site>/ directory before inventing an approach.

Usage

browser-harness <<'PY'
print(page_info())
PY

• Invoke as browser-harness. Use heredocs for multi-line commands.
• Helpers are pre-imported. run.py calls ensure_daemon() before exec.
• First navigation for a task is new_tab(url), not goto_url(url). The daemon preserves the attached tab across separate CLI invocations, so do not call new_tab() again in every script.
• Keep one working tab per task/site. Before opening another, inspect current_tab() and list_tabs() and use switch_tab() to reuse a matching tab. Do not leave duplicate tabs on the same URL or close tabs you did not create.
• At task completion, close tabs created for the task that are no longer needed. Keep a tab open if the user needs to see it, it is needed for a known follow-up, or closing it could discard unsaved work or other important state.
• new_tab() and switch_tab() attach and move the horse marker without changing Chrome's visible tab. Screenshots and normal CDP input work in the background. Never call activate_tab(target) automatically: it brings Chrome to the foreground. Call it only when the user explicitly asks to see or visibly switch to that tab. Do not pair switch_tab() with activate_tab().
• A local daemon is a connection to the whole Chrome instance, not to one site, task, card, or agent. Omit BU_NAME and reuse the default daemon for normal sequential local work across websites, tabs, screenshots, and Codex turns. Do not invent per-job names such as gmail1375 or slack1371: every new local daemon opens another browser-level CDP connection and Chrome may show another Allow prompt.
• Set BH_TAB_MARKER=0 before starting the daemon to leave page titles unchanged. The horse marker remains enabled by default.
• A timeout or page that pauses while hidden is not permission to foreground Chrome. Keep using background CDP operations. For a focus-gated page, temporarily call cdp("Emulation.setFocusEmulationEnabled", enabled=True), perform and verify the operation, then disable it in a finally block. If background control still cannot work, report that limitation instead of activating the tab. Do not invent a Runtime.evaluate scroll replacement or a cross-frame JS walker.
• The normal local flow attaches to the running Chrome/Chromium CDP endpoint. No browser ids or local profile selection.

Local Chrome

The default daemon can keep many tabs and visit many sites; browser-harness has no per-site, screenshot, or result-count limit that requires a new daemon. Chrome memory and page complexity are the practical limits. Reuse matching tabs with list_tabs() and switch_tab().

One daemon has one mutable attached/current tab. Many agents can share it when their browser operations are serialized: treat local Chrome as one shared browser lane while non-browser work continues in parallel. Sequential tab switching, input, and screenshot capture are safe. Do not create another local daemon merely because several agents exist.

Two agents that switch tabs and act simultaneously can race, causing one to act on or capture the other's tab. For truly simultaneous interactive work, use separate remote browsers when Browser Use Cloud authentication is already available. Otherwise serialize browser operations through the default local daemon. A named local daemon is a last resort when simultaneous isolation is required, remote auth is unavailable or unsuitable, and the extra Chrome approval prompt is acceptable. It creates another controller and dedicated tab in the same local Chrome profile, not another Chrome profile or process.

If the default daemon becomes stale, use its built-in reattachment/recovery first. A command timeout, truncated output, site change, closed tab, or new task is not a reason to create another daemon. Run browser-harness --doctor and restart or replace the default daemon only when it is actually dead or cannot recover.

If the daemon cannot connect, run diagnostics:

browser-harness --doctor

If Chrome is not running at all, the harness launches it automatically and retries.

If Chrome is running but remote debugging is not enabled, the harness opens:

chrome://inspect/#remote-debugging

On macOS, when local Chrome asks for remote-debugging permission, keep the original browser command running and call mac-approve in another shell/tool call. Preserve the exact daemon name: if the waiting command used BU_NAME=r7k2, run:

BU_NAME=r7k2 browser-harness mac-approve

For the default daemon, omit the BU_NAME prefix. The original command resumes when the helper returns ready; do not rerun it. If the helper reports accessibility-required, ask the user once to grant the app launching browser-harness (for example Terminal, iTerm, or Codex) access in System Settings > Privacy & Security > Accessibility, then call mac-approve once again. This is only for local Chrome; do not call it for BU_CDP_URL, BU_CDP_WS, or Browser Use Cloud.

When the shell tool can yield a still-running process, use a short 3-5 second initial yield for the first local command, not a 30-second wait. If the command yields with the Allow hint, leave that exact process running, immediately call browser-harness mac-approve in a second tool call, then resume or poll the original process. With a named daemon, preserve its exact BU_NAME for the helper. Never start the browser command again. If the user clicks Allow first, the same handshake completes and the original command returning successfully is the agent's feedback; mac-approve also returns ready when the daemon is already connected.

mac-approve is macOS-only. On Linux or Windows, keep the original browser command running and ask the user to click Allow if Chrome presents the approval dialog. Their click completes the same handshake, so resume or poll the original process for success; do not rerun it or create a replacement daemon. If that Chrome build presents no approval dialog, the original command simply connects.