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 read <url> --outline                          # page as text, no browser
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.

Reading Pages as Text: read

To get a page's content as agent-readable text, use read before reaching for a browser session. It launches nothing when given a URL.

agent-browser read https://docs.example.com/guide                 # markdown if the site serves it, else extracted text
agent-browser read https://docs.example.com/guide --outline       # heading outline only, cheapest way to scan a page
agent-browser read https://docs.example.com --llms index          # nearest llms.txt links
agent-browser read https://docs.example.com --llms full --filter auth   # llms-full.txt, only matching sections
agent-browser read                                                # no URL: the rendered DOM of the active tab

An explicit URL is fetched with Accept: text/markdown, then retried with .md appended, then the ancestor paths are searched for a matching llms.txt, and last it falls back to text extracted from the HTML. Useful flags: --filter <text> (keep matching sections), --require-md (fail unless the response is real markdown), --raw (body unextracted), --max-output <chars>, --json. With no URL, read needs an open page (open <url> and wait --load networkidle first), which makes it the way to extract a JS-rendered page after it settles. --llms and --require-md need an HTTP resource, so without a URL they use the active tab's URL.

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:

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 (needs Node.js: fnm install --lts or brew install node; 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