Browser Harness (Self-Healing LLM Browser Agent)

---
name: browser-harness-self-healing
description: Self-healing browser harness that gives LLMs complete freedom to complete any browser task via CDP, with auto-written helpers.
triggers:
  - set up browser harness
  - automate browser with LLM
  - self-healing browser agent
  - use browser-harness for web tasks
  - connect LLM to real browser
  - browser automation with CDP
  - install browser-use harness
  - run browser task with AI agent
---

# Browser Harness (Self-Healing LLM Browser Agent)

> Skill by [ara.so](https://ara.so) — Daily 2026 Skills collection.

Browser Harness is the simplest, thinnest self-healing harness that gives an LLM complete freedom to complete any browser task. It connects directly to Chrome via the Chrome DevTools Protocol (CDP) over a single WebSocket — no framework, no recipes, no rails. When a helper function is missing mid-task, the agent writes it into `helpers.py` and continues.

---

## Installation

### 1. Clone and read `install.md`

```bash
git clone https://github.com/browser-use/browser-harness
cd browser-harness
cat install.md

Always read install.md first — it covers the exact steps to install dependencies and connect to your real browser.

2. Install dependencies

pip install -r requirements.txt

3. Enable Chrome Remote Debugging

Launch Chrome with remote debugging enabled:

# macOS
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome \
  --remote-debugging-port=9222 \
  --user-data-dir=/tmp/chrome-debug

# Linux
google-chrome --remote-debugging-port=9222 --user-data-dir=/tmp/chrome-debug

# Windows
"C:\Program Files\Google\Chrome\Application\chrome.exe" ^
  --remote-debugging-port=9222 --user-data-dir=C:\tmp\chrome-debug

When the browser opens, tick the checkbox on the setup page to allow connection.

4. Start the daemon

python daemon.py

This launches the CDP WebSocket bridge and socket server that run.py and admin.py communicate through.

---

Core Files

File	Lines	Purpose
run.py	~36	Runs plain Python with helpers preloaded
helpers.py	~195	Starting tool calls; the agent edits this
admin.py	~180	Admin/bootstrap utilities
daemon.py	~181	CDP WebSocket + socket bridge
install.md	—	First-time install guide
SKILL.md	—	Day-to-day usage reference

---

Running Tasks

Basic usage

python run.py

run.py imports helpers.py and drops into an interactive loop where the agent (or you, as the agent) can call any helper directly.

Example: star a GitHub repository

# Inside run.py context — helpers are already imported
navigate("https://github.com/browser-use/browser-harness")
click('[aria-label="Star this repository"]')

Example: fill a form

navigate("https://example.com/form")
type_text("#name", "Jane Doe")
type_text("#email", "[email protected]")
click('button[type="submit"]')
wait_for_selector(".success-message")

---

helpers.py — Key Functions

Read helpers.py every time before writing a task — the agent edits it and functions evolve. Typical starting helpers:

# Navigate to a URL
navigate(url: str)

# Click an element by CSS selector
click(selector: str)

# Type text into an input
type_text(selector: str, text: str)

# Wait for an element to appear
wait_for_selector(selector: str, timeout: int = 5000)

# Get text content of an element
get_text(selector: str) -> str

# Evaluate arbitrary JS in the page
evaluate(js: str) -> Any

# Take a screenshot (returns base64 PNG)
screenshot() -> str

# Scroll the page
scroll(x: int, y: int)

# Upload a file (agent writes this if missing)
upload_file(selector: str, path: str)

Self-healing pattern: If a function doesn't exist yet, the agent appends it to helpers.py and continues:

● agent: wants to upload a file
│
● helpers.py → upload_file() missing
│
● agent edits helpers.py                helpers.py  192 → 199 lines
│                                                   + upload_file()
✓ file uploaded

---

CDP / WebSocket Architecture

  Agent (Python) → run.py → helpers.py
                                │
                           socket bridge
                                │
                           daemon.py
                                │
                      CDP WebSocket (port 9222)
                                │
                          Chrome browser

• daemon.py holds the persistent CDP connection
• All helper calls go through the socket bridge — no direct CDP in user code
• The agent only touches helpers.py and run.py

---

Remote Browsers (Free Tier)

For sub-agents or deployment without a local browser:

1. Get a free API key (3 concurrent browsers, no card): cloud.browser-use.com/new-api-key
2. Or let the agent sign up via docs.browser-use.com/llms.txt

# Set your key before starting daemon
import os
os.environ["BROWSER_USE_API_KEY"] = "your-key-here"  # use env var, never hardcode

Or export in shell:

export BROWSER_USE_API_KEY=$BROWSER_USE_API_KEY
python daemon.py

---

Domain Skills

Pre-learned skills for specific sites live in domain-skills/:

domain-skills/
  github/
  linkedin/
  amazon/
  ...

Each skill teaches the agent site-specific selectors, flows, and edge cases. Skills are written by the harness, not by you — run your task, and when the agent figures out something non-obvious, it files the skill itself.

To use an existing skill, the agent reads it automatically when navigating to a matching domain. To contribute, open a PR with the generated domain-skills/<site>/ folder.

---

Setup Prompt (for Claude Code / Codex / Cursor)

Paste this to bootstrap the entire setup:

Set up https://github.com/browser-use/browser-harness for me.

Read `install.md` first to install and connect this repo to my real browser.
Then read `SKILL.md` for normal usage. Always read `helpers.py` because that
is where the functions are. When you open a setup or verification tab, activate
it so I can see the active browser tab. After it is installed, if I am already
logged in to GitHub, star this repository as a small verification task; if I
am not logged in, just go to browser-use.com.

---

Common Patterns

Pattern: navigate and extract data

navigate("https://news.ycombinator.com")
titles = evaluate("""
  Array.from(document.querySelectorAll('.titleline > a'))
    .map(a => a.textContent)
    .slice(0, 10)
""")
print(titles)

Pattern: wait and retry

navigate("https://example.com/slow-page")
wait_for_selector(".data-table", timeout=10000)
rows = evaluate("""
  Array.from(document.querySelectorAll('.data-table tr'))
    .map(r => r.innerText)
""")

Pattern: handle auth (already logged in)

# The harness uses your real Chrome profile — cookies and sessions are live
navigate("https://github.com")
# If already logged in, your session is active immediately
click('a[href="/new"]')

Pattern: agent writes a missing helper

# Agent detects upload_file is missing, appends to helpers.py:
def upload_file(selector: str, path: str):
    abs_path = os.path.abspath(path)
    node_id = _get_node_id(selector)
    _cdp("DOM.setFileInputFiles", {"files": [abs_path], "nodeId": node_id})

---

Troubleshooting

Daemon won't connect

• Confirm Chrome is running with --remote-debugging-port=9222
• Visit http://localhost:9222/json — you should see open tabs as JSON
• Make sure no other process owns port 9222

lsof -i :9222   # macOS/Linux
netstat -ano | findstr 9222   # Windows

Helper function raises AttributeError

• Read helpers.py — the function may have been renamed or not yet written
• If missing, add it to helpers.py following the existing CDP call pattern
• Restart run.py after editing helpers.py

Page state is stale after navigation

wait_for_selector("body", timeout=3000)
# or
evaluate("document.readyState")  # should return 'complete'

Selector not found

# Debug: dump all matching selectors
evaluate("document.querySelectorAll('button').length")
evaluate("document.querySelector('button')?.textContent")
# Use broader selectors if the page structure changed
click('button:contains("Submit")')  # via JS evaluate if needed

Remote browser key errors

# Verify key is set
echo $BROWSER_USE_API_KEY
# Re-export and restart daemon
export BROWSER_USE_API_KEY=bu_...
python daemon.py

---

Key References

• install.md — authoritative install steps
• SKILL.md — day-to-day usage (always read before a task)
• helpers.py — live function reference (always read; changes mid-task)
• Bitter Lesson post
• Skills post
• cloud.browser-use.com — remote browsers
• docs.browser-use.com/llms.txt — LLM-readable docs