browser-harness

browser-harness

Direct browser control via CDP. You drive the user's real browser with a Rust-native CLI through the browser-harness command.

Prerequisite (one-time — NOT part of the AI workflow)

This skill is instructions only. It assumes the browser-harness command is already on $PATH. If command -v browser-harness fails, do the one-time install in references/install.md first, then continue. Installation and browser-connection setup are a prerequisite; once browser-harness page-info prints page info, never run install/connection steps again as part of normal work.

Usage

browser-harness new-tab <<'JSON'
{"daemon_name":"default","url":"https://docs.browser-use.com"}
JSON

browser-harness page-info <<'JSON'
{"daemon_name":"default"}
JSON

• Invoke as browser-harness — it's on $PATH after install. No cd, no cargo run.
• Use the heredoc form with <<'JSON' for every multi-line command. It prevents shell quote mangling.
• First navigation is new-tab(url), not goto(url) — goto runs in the user's active tab and clobbers their work.
• The daemon auto-starts; you never start/stop it manually unless you want to.

What actually works

• Screenshots first. browser-harness screenshot to understand the page, find visible targets, and decide whether you need a click, a selector, or more navigation.
• Clicking. browser-harness screenshot → read the pixel off the image → browser-harness click-at-xy → browser-harness screenshot to verify. Suppress the Playwright-habit reflex of "locate first, then click" — no getBoundingClientRect, no selector hunt. Drop to DOM only when the target has no visible geometry. Hit-testing happens in Chrome's browser process, so clicks pass through iframes / shadow DOM / cross-origin without extra work.
• Bulk HTTP. browser-harness http-get. No browser needed for static pages.
• After goto: browser-harness wait-for-load.
• Wrong/stale tab: browser-harness ensure-real-tab.
• Verification: browser-harness page-info is the simplest "is this alive?" check; screenshots are the default way to verify whether a visible action worked.
• DOM reads: use browser-harness js for inspection/extraction when a screenshot shows coordinates are the wrong tool.
• SPA waits: browser-harness wait-for-element, browser-harness fill-input, browser-harness wait-for-network-idle.
• Auth wall: redirected to login → stop and ask the user. Don't type credentials from screenshots.
• Raw CDP for anything helpers don't cover: browser-harness cdp.

After every meaningful action, re-screenshot before assuming it worked.

Remote / cloud browsers

Use remote for parallel sub-agents (each gets an isolated browser via a distinct BU_NAME) or on a headless server. BROWSER_USE_API_KEY must be set.

browser-harness create-browser <<'JSON'
{"timeout":120}
JSON

BU_NAME=work browser-harness ensure-daemon <<'JSON'
{"name":"work","env":{"BU_CDP_WS":"<cdpWsUrl-from-create-browser>","BU_BROWSER_ID":"<browser-id>"}}
JSON

BU_NAME=work browser-harness new-tab <<'JSON'
{"daemon_name":"work","url":"https://example.com"}
JSON

create-browser returns id, cdpWsUrl, and liveUrl. Share liveUrl with the user if they need to watch. Running remote daemons bill until timeout.

Interaction skills (progressive disclosure)

If you struggle with a specific UI mechanic, read the matching file under ${CLAUDE_PLUGIN_ROOT}/interaction-skills/ before inventing an approach. Available: browser-wall, connection, cookies, cross-origin-iframes, dialogs, downloads, drag-and-drop, dropdowns, iframes, network-requests, print-as-pdf, profile-sync, screenshots, scrolling, shadow-dom, tabs, uploads, viewport.

Domain skills (opt-in)

Community per-site playbooks live in ${CLAUDE_PLUGIN_ROOT}/domains/<host>/ and are off by default. Set BH_DOMAIN_SKILLS=1 to enable them; when enabled and the task is site-specific, read every file in the matching <site>/ directory before inventing an approach.

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.
• Prefer compositor-level actions (screenshots, coordinate clicks, raw key input) over framework/DOM hacks. Reach for interaction-skills/ only when those are the wrong tool.
• The CLI is Rust-native; all operations accept JSON via stdin heredocs.