Browser Harness

browser-harness

When to Use

• Use when a task needs a real logged-in browser, visible interaction, or JS-heavy page control.
• Use when static fetches are insufficient and CDP browser automation is appropriate.

Direct browser control via CDP. For task-specific edits, use agent-workspace/agent_helpers.py. For setup, install, or connection problems, read install.md.

Routing check first: if the task needs no interaction (no clicks, logins, or forms) and you just want page content, use DeepAPI POST /v1/scrape/website instead of driving a browser — see the deepapi skill. Use browser-harness when the task needs a real browser: interaction, JS-heavy flows, logged-in sessions, or visual verification.

Domain skills (community-contributed per-site playbooks under agent-workspace/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 agent-workspace/domain-skills/<site>/ directory before inventing an approach.

Usage

browser-harness -c '
new_tab("https://docs.browser-use.com")
wait_for_load()
print(page_info())
'

• Invoke as browser-harness — it's on $PATH. No cd, no uv run.
• First navigation is new_tab(url), not goto_url(url) — goto runs in the user's active tab and clobbers their work.

Tool call shape

browser-harness -c '
# any python. helpers pre-imported. daemon auto-starts.
'

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

Remote browsers

Use remote for parallel sub-agents (each gets its own isolated browser via a distinct BU_NAME) or on a headless server. BROWSER_USE_API_KEY must be set. start_remote_daemon, list_cloud_profiles, list_local_profiles, sync_local_profile are pre-imported.

When supervising those sub-agents, after each check send the user one very short status line: what they are doing and whether they are on track.

Claude Code cmux note: after Claude finishes, it may prefill a predicted next user message; that draft is Claude, not the user speaking.

browser-harness -c '
start_remote_daemon("work")                               # default — clean browser, no profile
# start_remote_daemon("work", profileName="my-work")      # reuse a cloud profile (already logged in)
# start_remote_daemon("work", profileId="<uuid>")         # same, but by UUID
# start_remote_daemon("work", proxyCountryCode="de", timeout=120)   # DE proxy, 2-hour timeout
# start_remote_daemon("work", proxyCountryCode=None)      # disable the Browser Use proxy
'

BU_NAME=work browser-harness -c '
new_tab("https://example.com")
print(page_info())
'

start_remote_daemon prints liveUrl and auto-opens it in the local browser (if a GUI is detected) so the user can watch along. Headless servers print only — share the URL with the user. The daemon PATCHes the cloud browser to stop on shutdown, which persists profile state. Running remote daemons bill until timeout.

Profiles (cookies-only login state) live in interaction-skills/profile-sync.md — covers list_cloud_profiles(), the chat-driven "which profile?" pattern, and sync_local_profile() for uploading a local Chrome profile.

Interaction skills

If you start struggling with a specific mechanic while navigating, look in interaction-skills/ for helpers. They cover reusable UI mechanics like dialogs, tabs, dropdowns, iframes, and uploads. The available interaction skills are:

• connection.md
• 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
• profile-sync.md
• screenshots.md
• scrolling.md
• shadow-dom.md
• tabs.md
• uploads.md
• viewport.md

What actually works

• Screenshots first: use capture_screenshot() to understand the current page quickly, find visible targets, and decide whether you need a click, a selector, or more navigation.
• Clicking: capture_screenshot() → read the pixel off the image → click_at_xy(x, y) → capture_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 (hidden input, 0×0 node). Hit-testing happens in Chrome's browser process, so clicks go through iframes / shadow DOM / cross-origin without extra work.
• 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(). Use it when the current tab is stale or internal; the daemon also auto-recovers from stale sessions on the next call.
• Verification: print(page_info()) is the simplest "is this alive?" check, but screenshots are the default way to verify whether a visible action actually worked.
• DOM reads: use js(...) for inspection and extraction when the screenshot shows that coordinates are the wrong tool.
• Iframe sites (Azure blades, Salesforce): click_at_xy(x, y) passes through; only drop to iframe DOM work when coordinate clicks are the wrong tool.
• 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.
• Core helpers stay short. Put task-specific helper additions in agent-workspace/agent_helpers.py; daemon/bootstrap and remote session admin live in the core package.
• Don't add a manager layer. No retries framework, session manager, daemon supervisor, config system, or logging framework.

Hermes Agent integration

Installed at ~/Developer/browser-harness as editable uv tool install -e .. Binary at ~/.local/bin/browser-harness. Skill at ~/.hermes/skills/browser-harness/.

Frontmatter pitfall: The upstream SKILL.md ships with name: browser in frontmatter, which collides with Hermes's built-in browser toolset. When copying into ~/.hermes/skills/, rename to name: browser-harness in the frontmatter or Hermes will shadow/conflict with its own browser tools.

Brave Browser: Works identically to Chrome. Enable remote debugging at brave://inspect/#remote-debugging (same checkbox). The harness auto-discovers Brave's profile directory.

Authenticated content extraction (proven pattern)

browser-harness connects to the user's real browser with their active sessions — ideal for extracting content from login-walled sites where web_extract or Hermes's built-in browser_navigate fail (e.g. X/Twitter articles, LinkedIn, paywalled sites).

Pattern:

browser-harness -c '
new_tab("https://x.com/user/status/123456")
wait_for_load()
import time
time.sleep(5)  # let JS-heavy pages render
text = js("""
    const article = document.querySelector("article");
    if (article) return article.innerText;
    return document.body.innerText;
""")
with open("/tmp/extracted.txt", "w") as f:
    f.write(text)
print("Written", len(text), "chars")
'

• Write to a temp file to avoid shell escaping issues with large text
• Use time.sleep() generously for JS-heavy SPAs (X, LinkedIn need 3-5s)
• X/Twitter articles render inline — just scroll/extract via DOM, no extra click needed
• For very long pages, js(...) with innerText grabs everything including below-fold content

Hermes Agent integration

Installed at ~/Developer/browser-harness as editable uv tool install -e .. Binary at ~/.local/bin/browser-harness. Skill at ~/.hermes/skills/browser-harness/.

Frontmatter pitfall: The upstream SKILL.md ships with name: browser in frontmatter, which collides with Hermes's built-in browser toolset. When copying into ~/.hermes/skills/, rename to name: browser-harness in the frontmatter.

Brave Browser: Works identically to Chrome. Enable remote debugging at brave://inspect/#remote-debugging (same checkbox). The harness auto-discovers Brave's profile directory.

Authenticated content extraction (proven pattern)

browser-harness connects to the user's real browser with active sessions — ideal for login-walled sites where web_extract or Hermes's built-in browser_navigate fail (X/Twitter articles, LinkedIn, paywalled sites).

browser-harness -c '
new_tab("https://x.com/user/status/123456")
wait_for_load()
import time
time.sleep(5)  # let JS-heavy pages render
text = js("""
    const article = document.querySelector("article");
    if (article) return article.innerText;
    return document.body.innerText;
""")
with open("/tmp/extracted.txt", "w") as f:
    f.write(text)
print("Written", len(text), "chars")
'

• Write to a temp file to avoid shell escaping issues with large text
• Use time.sleep() generously for JS-heavy SPAs (X, LinkedIn need 3-5s)
• X/Twitter articles render inline — just scroll/extract via DOM, no extra click needed
• js(...) with innerText grabs everything including below-fold content

Gotchas (field-tested)

• Brave Browser uses brave://inspect/#remote-debugging instead of chrome://inspect/.... The harness auto-discovers Brave's data dir.
• Login-walled content extraction (e.g. X/Twitter articles): navigate with new_tab(url), wait_for_load(), then extract via js("document.querySelector('article').innerText"). Write to a temp file to avoid shell escaping: with open('/tmp/out.txt', 'w') as f: f.write(text). The user's existing browser session handles auth automatically.
• 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.
• 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"}.
• After every meaningful action, re-screenshot before assuming it worked. Use the image to verify changed state, open menus, navigation, visible errors, and whether the page is in the state you expected.
• Use screenshots to drive exploration. They are often the fastest way to find the next click target, notice hidden blockers, and decide if a selector is even worth writing.
• Prefer compositor-level actions over framework hacks. Try screenshots, coordinate clicks, and raw key input before adding DOM-specific workarounds.
• If you need framework-specific DOM tricks, check interaction-skills/ first. That is where dropdown, dialog, iframe, shadow DOM, and form-specific guidance belongs.

Domain skills (opt-in)

Only applies when BH_DOMAIN_SKILLS=1. Otherwise ignore — agent-workspace/domain-skills/ is dormant and goto_url won't surface skill files.

When enabled, search agent-workspace/domain-skills/<host>/ before inventing an approach. goto_url returns up to 10 skill filenames for the navigated host.

If you learn anything non-obvious — a private API, stable selector, framework quirk, URL pattern, hidden wait, or site-specific trap — open a PR to agent-workspace/domain-skills/<site>/. Capture the durable shape of the site (the map, not the diary). Don't write pixel coordinates (break on layout), task narration, or secrets — the directory is public.

Limitations

• Adapted from davidondrej/skills; verify local paths, tools, credentials, and agent features before acting.
• For commands, remote access, scheduling, browser automation, or file-changing workflows, get explicit user approval and confirm the target environment first.