What is test-browser?

A browser-testing command that runs end-to-end checks on pages affected by a pull request or code branch using the agent-browser command-line tool.

Use it to identify affected pages, open them in headless Chromium, exercise important workflows, and check their visual output and console behavior.

It can catch problems that unit tests may miss, such as broken JavaScript integration, layout regressions, failed user workflows, and browser console errors.

test-browser — Command for coding agents by tajmahal226: A browser-testing command that runs end-to-end checks on pages…

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add commands/tajmahal226/compound-engineering-plugin/test-browser

Clone the repo

git clone --depth 1 https://github.com/tajmahal226/compound-engineering-plugin

Or install compound-engineering, the plugin that ships this one along with the rest of its 20 skills, 17 commands, 1 MCP server.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/commands/tajmahal226/compound-engineering-plugin/test-browser.svg)](https://agentmods.dev/commands/tajmahal226/compound-engineering-plugin/test-browser)

Your own site

<a href="https://agentmods.dev/commands/tajmahal226/compound-engineering-plugin/test-browser"><img src="https://agentmods.dev/badge/commands/tajmahal226/compound-engineering-plugin/test-browser.svg" alt="Measured on agentmods" height="20"></a>

Per session 14 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 2,067 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00014	$0.02067
Opus 5	$0.00007	$0.01033
Sonnet 5	$0.00003	$0.00413
Haiku 4.5	$0.00001	$0.00207

Measured 4d ago against content hash e1f981b08ed1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-browser 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 4d 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

test-browser — 86% identical, 31 lines differ

plugins/compound-engineering/commands/test-browser.md · 340 lines

How it starts

The opening of the file, as written. The whole thing — 340 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Browser Test Command

<command_purpose>Run end-to-end browser tests on pages affected by a PR or branch changes using agent-browser CLI.</command_purpose>

CRITICAL: Use agent-browser CLI Only

DO NOT use Chrome MCP tools (mcp__claude-in-chrome__*).

This command uses the agent-browser CLI exclusively. The agent-browser CLI is a Bash-based tool from Vercel that runs headless Chromium. It is NOT the same as Chrome browser automation via MCP.

If you find yourself calling mcp__claude-in-chrome__* tools, STOP. Use agent-browser Bash commands instead.

Introduction

QA Engineer specializing in browser-based end-to-end testing

This command tests affected pages in a real browser, catching issues that unit tests miss:

JavaScript integration bugs
CSS/layout regressions
User workflow breakages
Console errors

Prerequisites

Setup

Check installation:

command -v agent-browser >/dev/null 2>&1 && echo "Installed" || echo "NOT INSTALLED"

Install if needed:

npm install -g agent-browser
agent-browser install  # Downloads Chromium (~160MB)

See the agent-browser skill for detailed usage.

Main Tasks

0. Verify agent-browser Installation

Before starting ANY browser testing, verify agent-browser is installed:

command -v agent-browser >/dev/null 2>&1 && echo "Ready" || (echo "Installing..." && npm install -g agent-browser && agent-browser install)

If installation fails, inform the user and stop.

1. Ask Browser Mode

<ask_browser_mode>

Before starting tests, ask user if they want to watch the browser:

Use AskUserQuestion with:

Question: "Do you want to watch the browser tests run?"
Options:
1. Headed (watch) - Opens visible browser window so you can see tests run
2. Headless (faster) - Runs in background, faster but invisible

Read the full file on GitHub · 340 lines

Changes

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.

4d ago First seen · 340 lines · 14 tokens per session scan A e1f981b08ed1

Subscribe to this mod's changes

test-browser is a command published in the GitHub repository tajmahal226/compound-engineering-plugin (4 stars, last pushed 6mo ago), licensed MIT. It adds 14 tokens to every session and 2,067 once invoked, about $0.0001 per session on Opus 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 2026-08-31.

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test-browser