Browser Harness connects a language model to a real browser through an editable CDP WebSocket, allowing the agent to perform browser tasks and create reusable helpers when needed. Developers and browser agents use it for browser automation, with an MCP server available for compatible clients. The catalogue entries provide setup instructions and teach coding agents its browser workflow.
Borrowing it
Nothing to install: this file belongs to browser-use/browser-harness. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/browser-use/browser-harness/main/AGENTS.mdgit clone --depth 1 https://github.com/browser-use/browser-harnessWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/browser-use/browser-harness/agents-md)<a href="https://agentmods.dev/instructions/browser-use/browser-harness/agents-md"><img src="https://agentmods.dev/badge/instructions/browser-use/browser-harness/agents-md/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/browser-use/browser-harness/agents-md"><img src="https://agentmods.dev/badge/instructions/browser-use/browser-harness/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00506 | $0.00506 |
| Opus 5.5 | $0.00202 | $0.00202 |
| Sonnet 5.5 | $0.00101 | $0.00101 |
| Haiku 4.5 | $0.00051 | $0.00051 |
Grade A, and why
browser-harness AGENTS.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 57 lines — stays where its author put it; the contents beside it link to each section on GitHub.
browser-harness is a thin layer that connects agents to browsers via an editable CDP harness.
Code priorities
- Clarity
- Precision
- Low verbosity
- Versatility
Overview
Core code lives in src/browser_harness/:
admin.py— daemon lifecycle, diagnostics, updates, profile managementdaemon.py— the long-lived middleman process between the browser and the agenthelpers.py— CDP wrapper and core browser primitives auto-imported into the scripts the CLI reads from stdinrun.py— thebrowser-harnessCLI
SKILL.md tells agents how to use the harness and CLI.
install.md tells agents how to install it, attach a browser, and troubleshoot.
An agent operating the harness only edits inside agent-workspace/:
agent_helpers.py— task-specific browser helpers the agent addsdomain-skills/— skills the agent writes and reads
Package/CLI name = browser-harness. Skill identity (name + trigger) = browser-use (do not rename).
Commands
From a git checkout (no global install required for local testing):
# doctor — install/daemon/browser state
./browser-harness --doctor
# smoke — CDP attach + page_info (Chrome remote debugging must be allowed)
./browser-harness <<'PY'
print(page_info())
PY
# unit tests (no live browser)
uv run --with pytest python -m pytest tests/unit -q
# after core/src edits: reload daemon so next call picks up code
./browser-harness --reload
Notes:
./browser-harness= local tree launcher. Agents/docs outside this repo use the installedbrowser-harnesscommand.- Integration tests under
tests/integration/may need a live browser/CDP — prefer unit + doctor for routine PR gates. - First-time install / blocked Chrome: follow
install.md(chrome://inspect/#remote-debugging).
Security
- Do not commit secrets, Browser Use Cloud tokens, or session cookies.
- Prefer the smallest change that fixes the bug; do not expand CDP surface without need.
Contributing
Consider what is really needed. Prefer the smallest diff that fixes the bug.
Domain skills under agent-workspace/domain-skills/ are agent-generated when possible — hand-author only when necessary.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago Changed · +25 lines · +190 tokens per session 86dc889e7f18
- 1mo ago First seen · 32 lines · 316 tokens per session scan A 80b1176f8e91
browser-harness AGENTS.md is an instructions file published in the GitHub repository browser-use/browser-harness (18,486 stars, last pushed 2d ago), licensed MIT. It adds 506 tokens to every session, about $0.0020 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deepseek-harness AGENTS.md
AGENTS.md instructions for deepseek-ai/deepseek-harness, covering agents.md, pre-stable apis and released session data, repository layout, commands and host sandbox failures.