Agent Browser

agent-browser

Overview

agent-browser is an open-source browser automation CLI from Vercel Labs, built for LLM interaction with a snapshot + refs system: instead of a full DOM, snapshot returns an accessibility tree of just the interactive elements (buttons, inputs, links) with semantic labels, each tagged with a stable @e1-style ref. Full DOM dumps run 5000+ nodes / 200KB of context; an accessibility-tree snapshot is 50-100 elements / ~10KB, roughly a 93% reduction. Refs also survive re-renders, so they don't need re-deriving after every DOM tweak the way CSS selectors do.

See When to Use vs Playwright for when this CLI beats DOM-based tools.

Installation

# macOS (preferred — managed by Homebrew)
brew install agent-browser

# Linux / fallback
npm install -g agent-browser

# Install browser binaries after either method
agent-browser install

# Linux: also install system dependencies
agent-browser install --with-deps

# Verify health
agent-browser doctor

Quick Start

Basic Workflow

# 1. Navigate to a page
agent-browser open https://example.com

# 2. Get snapshot with refs
agent-browser snapshot -i

# Output shows:
# textbox "Email" [ref=e1]
# textbox "Password" [ref=e2]
# button "Submit" [ref=e3]

# 3. Interact using refs
agent-browser fill @e1 "user@example.com"
agent-browser fill @e2 "password123"
agent-browser click @e3

# 4. Wait and verify
agent-browser wait --load networkidle
agent-browser snapshot -i

Refs are invalidated whenever the page changes (navigation, dropdown opening, DOM re-render). Re-run snapshot -i after any action that could change the page before reusing a ref: an ref from before the action may now point at a different element or nothing at all.

Session Management

Always pass --session: one named session per project prevents stale daemons from accumulating across parallel agent sessions.

# Use project name as session (run this pattern everywhere)
agent-browser --session "$(basename "$PWD")" open https://app.com

# Authenticated flows: add persistent profile (gitignored)
agent-browser --session "$(basename "$PWD")" --profile .claude/browser-profile open https://app.com/login

# Stateless scraping/extraction: use Lightpanda instead (10x less memory)
agent-browser --session "$(basename "$PWD")" --engine lightpanda open https://public-site.com

# List all active sessions
agent-browser session list

# Diagnose + clean stale sockets (run when things feel wrong)
agent-browser doctor --fix

# Close this project's session only (never use --all with parallel projects)
agent-browser close --session "$(basename "$PWD")"

Engine Choice

Rule: if it only reads public pages and needs no login or screenshot → Lightpanda. Otherwise Chrome.

Command Cheat Sheet

agent-browser --session "$(basename "$PWD")" open <url>   # navigate
agent-browser snapshot -i                                  # get @refs
agent-browser click @e1                                    # click
agent-browser fill @e2 "text"                               # fill a field
agent-browser wait --load networkidle                       # wait for load
agent-browser get text @e3                                  # read element
agent-browser is visible @e1                                 # verify state
agent-browser screenshot page.png                            # capture
agent-browser close --session "$(basename "$PWD")"          # cleanup

Full command surface (navigation, all interactions, find semantic locators, waits, screenshots/video, tabs, network, cookies, auth, MCP server, global flags) lives in references/commands.md.

Verify Before You Claim

Browser automation's core failure mode is confidently reporting page state nobody actually read. Before writing any claim into your final report:

• Every claimed value traces to a command. A total, a heading, a success banner: read it with get text / get value (or a snapshot that covers it) and quote the exact string returned. Never restate a value from the test plan or a product label as if it were observed on the page.
• snapshot -i hides non-interactive content. Totals, prices, and confirmation banners often live in a <span>/<div>, not a button or input: -i won't surface them. Use plain snapshot or get text <selector> to reach them.
• A screenshot filename is a claim. Confirm you're on the expected page (get url or a snapshot heading) immediately before calling screenshot, and name the file after what you just confirmed, not what you set out to capture.
• Own every process you start. If the task needs a local server to test against, announce it when you start it (command, port, PID) and stop it before finishing: state the kill explicitly. "Closed the browser session" is not the same claim as "shut down the app."

Worked Examples

Login and verify

agent-browser --session myapp open https://app.example.com/login
agent-browser snapshot -i
agent-browser fill @e1 "user@example.com"
agent-browser fill @e2 "password123"
agent-browser click @e3
agent-browser wait --load networkidle
agent-browser get url               # confirm redirected off /login
agent-browser close --session myapp

Scrape a public listing (stateless)

agent-browser --session catalog --engine lightpanda open https://shop.example.com/catalog
agent-browser get count ".product-card"
agent-browser snapshot -i -s ".product-card"
agent-browser close --session catalog

Verify state before asserting success

agent-browser --session checkout open http://localhost:3000/cart
agent-browser snapshot -i
agent-browser click @e4             # Add to cart
agent-browser get text .cart-total  # read the total — e.g. "$9.99" — don't assume it changed
agent-browser click @e9             # Checkout
agent-browser wait --url "**/confirmation"
agent-browser get text @e2          # read the confirmation heading
agent-browser close --session checkout

Report only the strings those two get text calls actually returned, not a number copied from the test plan.

Test an app you started locally

python3 -m http.server 3111 --directory ./dist &   # note the PID
echo "started static server on :3111, pid $!"
agent-browser --session localtest open http://localhost:3111
agent-browser snapshot -i
agent-browser get url                # confirm you're on the expected page first
agent-browser screenshot cart-page.png              # name matches what get url just confirmed
agent-browser close --session localtest
kill %1                              # stop the server you started, before declaring done
echo "stopped server on :3111"

When to Use vs Playwright

Reference File Guide

Detailed reference material lives in bundled files, loaded on-demand, and is regenerated from the CLI's own agent-browser skills get core --full so it stays in sync with the installed version. Load each only when the task needs it:

• references/commands.md: load when you need a command signature, flag, or alias not covered by the cheat sheet above (navigation, interaction, find, wait, screenshot/video, settings, tabs, frames, network/console, MCP server, global flags).
• references/advanced.md: load for session-state persistence, authentication (login flows, OAuth, 2FA, cookie import), trust-boundary safety rules, proxy configuration, or Chrome DevTools profiling.
• references/workflows.md: load for the snapshot + ref model in depth, or video-recording patterns.

If these ever drift from the installed CLI, regenerate with agent-browser skills get core --full and re-split (see git history of this file for the split points).

Resources

Official Documentation

• GitHub: https://github.com/vercel-labs/agent-browser
• AGENTS.md: AI agent integration guide, bundled with the CLI
• CLI source: npx opensrc vercel-labs/agent-browser (fetches the actual source for reference: there is no vendored copy in this skill)

Environment Variables

AGENT_BROWSER_IDLE_TIMEOUT_MS   # Auto-close daemon after N ms idle (set 300000 in dotfiles)
AGENT_BROWSER_SESSION           # Default session name (set per-project in your agent config file)
AGENT_BROWSER_ENGINE            # Default engine: chrome | lightpanda
AGENT_BROWSER_EXECUTABLE_PATH   # Custom browser binary path
AGENT_BROWSER_EXTENSIONS        # Comma-separated extension paths
AGENT_BROWSER_PROVIDER          # Cloud provider (browseruse, browserbase, browserless)
AGENT_BROWSER_ENCRYPTION_KEY    # AES-256-GCM key for session state files (64-char hex)
AGENT_BROWSER_STREAM_PORT       # WebSocket port for streaming
AGENT_BROWSER_HOME              # Installation directory

Operational Rules

• Always pass --session <project-name>: prevents stale-socket accumulation across parallel sessions (can cause daemon OOM)
• Never run agent-browser close --all or kill the browser process globally: breaks other projects' parallel sessions
• Persistent profile directories (e.g. .claude/browser-profile/) must be in .gitignore: they contain plaintext cookies and login tokens
• Omit --profile for stateless work: persistent profiles accumulate browser cache; idle-timeout only reclaims RAM, not disk cache
• Run agent-browser doctor --fix when sessions feel stuck: cleans stale sockets without killing active sessions
• A test-target server you started is your process to stop: agent-browser close only tears down the browser session, not an app server; kill it explicitly and say so (see Verify Before You Claim)
• For the authoritative, version-matched command reference: agent-browser skills get core --full