Agent Browser

agent-browser

Overview

agent-browser is an open-source browser automation CLI from Vercel Labs, purpose-built for AI agents. Unlike traditional browser automation tools, it's designed from the ground up for LLM interaction with a snapshot + refs system that reduces context usage by up to 93% compared to Playwright MCP.

Key Advantages

• 93% less context overhead - Accessibility tree snapshots instead of full DOM
• Zero configuration - Ready to use after installation
• Semantic element targeting - @e1 refs instead of fragile CSS selectors
• Rust + Node.js architecture - Fast CLI with robust browser control
• Session isolation - Run multiple browsers with separate state
• AI-optimized output - Structured data perfect for LLM parsing

Architecture

Three-layer design for performance and reliability:

1. Rust CLI - Fast command parsing and daemon communication
2. Node.js Daemon - Playwright-based browser lifecycle management
3. Fallback Mode - Pure Node.js when native binaries unavailable

Installation

# Install globally via npm
npm install -g agent-browser

# Install browser dependencies
agent-browser install

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

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

Session Management

# Run multiple isolated browsers
agent-browser --session auth open https://app.com/login
agent-browser --session test open https://staging.com

# List all active sessions
agent-browser session list

# Clean up
agent-browser --session auth close

Snapshot + Refs System

The snapshot command is the core of agent-browser's AI optimization. It generates an accessibility tree - a structured, semantic representation of interactive elements.

Why Accessibility Trees?

Traditional tools expose full DOM trees with thousands of nodes. Accessibility trees contain only interactive elements (buttons, inputs, links) with semantic labels - exactly what AI agents need.

Comparison:

• Full DOM: 5000+ nodes, 200KB context
• Accessibility tree: 50-100 elements, 10KB context
• Savings: 93% reduction in token usage

Snapshot Modes

# Interactive elements only (recommended for AI)
agent-browser snapshot -i

# Full accessibility tree
agent-browser snapshot

# Compact format (fewer details)
agent-browser snapshot -c

# Limit tree depth (for large pages)
agent-browser snapshot -d 3

# Scope to specific section
agent-browser snapshot -s "#main-content"

Understanding Refs

Refs are stable identifiers assigned to interactive elements in snapshots:

textbox "Email address" [ref=e1]
  placeholder: "Enter your email"
  required: true

button "Sign In" [ref=e5]
  role: button
  enabled: true

Use refs in commands: @e1, @e5, etc.

Advantages over CSS selectors:

• Semantic and human-readable
• Survive DOM changes (stable across re-renders)
• No need to inspect HTML structure
• AI agents can reason about element purpose

Essential Commands

Navigation

# Open URL (auto-prepends https://)
agent-browser open example.com

# History control
agent-browser back
agent-browser forward
agent-browser reload

# Close browser
agent-browser close

Interaction

# Click elements
agent-browser click @e3
agent-browser dblclick @e5

# Fill forms (clears then types)
agent-browser fill @e1 "text"

# Type text (preserves existing content)
agent-browser type @e2 "additional text"

# Press keys
agent-browser press Enter
agent-browser press "Control+A"

# Checkboxes
agent-browser check @e4
agent-browser uncheck @e4

# Dropdowns
agent-browser select @e6 "Option 2"

# Hover (reveals hidden elements)
agent-browser hover @e7

# Scroll
agent-browser scroll 0 500
agent-browser scrollintoview @e8

# File upload
agent-browser upload @e9 /path/to/file.pdf

# Drag and drop
agent-browser drag @e10 @e11

Information Retrieval

# Get element data
agent-browser get text @e1
agent-browser get html @e2
agent-browser get value @e3        # Input field value
agent-browser get attr @e4 href    # Attribute value

# Page metadata
agent-browser get title
agent-browser get url

# Element metrics
agent-browser get count ".product-card"
agent-browser get box @e5          # Bounding box coordinates
agent-browser get styles @e6       # Computed CSS

State Verification

# Check element state before interaction
agent-browser is visible @e1
agent-browser is enabled @e2
agent-browser is checked @e3

Waiting

# Wait for element
agent-browser wait @e5

# Wait duration (milliseconds)
agent-browser wait 2000

# Wait for text
agent-browser wait --text "Success"

# Wait for URL pattern (glob)
agent-browser wait --url "**/dashboard"

# Wait for network idle
agent-browser wait --load networkidle

# Wait for JavaScript condition
agent-browser wait --fn "document.readyState === 'complete'"

Media Capture

# Screenshot (PNG)
agent-browser screenshot page.png
agent-browser screenshot page.png --full    # Full page scroll

# PDF export
agent-browser pdf document.pdf

# Video recording (webm)
agent-browser record start demo.webm
agent-browser click @e1
agent-browser record stop

Semantic Find Commands

Alternative to refs - use human-readable locators for direct targeting:

# By ARIA role
find role button click --name "Submit"
find role textbox fill --label "Email" "user@example.com"

# By text content
find text "Click here" click
find text "Exact Match" click --exact

# By form labels
find label "Username" fill "admin"

# By placeholder
find placeholder "Search..." fill "query"

# By alt text (images)
find alt "Logo" click

# By title attribute
find title "Close dialog" click

# By test ID
find testid "submit-btn" click

# Position-based
find first "button" click
find last ".item" click
find nth 2 ".card" click

When to use find vs refs:

• Refs - Reliable, AI-optimized, survives DOM changes
• Find - Quick one-off actions, human-readable scripts

When to Use vs Playwright

Use agent-browser when:

✓ AI agent automation - Optimized for LLM workflows ✓ CLI-first workflows - Simple command-line usage ✓ Context efficiency matters - 93% less token overhead ✓ Rapid prototyping - Zero configuration needed ✓ Multiple sessions - Easy session isolation ✓ Semantic targeting - Prefer accessibility tree over DOM

Use Playwright MCP when:

✓ Complex programmatic control - Full JavaScript API ✓ Advanced browser features - Service workers, device emulation ✓ Existing Playwright tests - Reuse test infrastructure ✓ Fine-grained control - Direct access to CDP ✓ TypeScript integration - Type-safe browser automation

Summary: agent-browser excels at AI-driven automation with minimal context. Playwright excels at programmatic control with maximum flexibility.

Reference File Guide

Detailed information is available in bundled reference files (loaded on-demand):

references/command-reference.md

Complete command documentation including:

• All command signatures and options
• Browser configuration (viewport, geolocation, headers)
• Storage management (cookies, localStorage)
• Network interception and mocking
• Multi-tab/window/frame operations
• Dialog handling
• JavaScript execution (eval)
• Global flags and environment variables

references/advanced-patterns.md

Advanced usage patterns:

• Authentication state persistence
• Parallel session workflows
• Network request interception
• File download handling
• Custom proxy configuration
• Cloud provider integration (BrowserUse, BrowserBase)
• Video recording workflows
• CDP (Chrome DevTools Protocol) integration

references/best-practices.md

Optimization and reliability guidance:

• Token efficiency strategies
• Error handling patterns
• Performance optimization
• Debugging techniques
• Common pitfalls and solutions
• Production deployment considerations

references/examples.md

Real-world scenarios:

• E-commerce checkout automation
• Form submission and validation
• Web scraping with pagination
• Screenshot testing
• Data extraction workflows
• Multi-step authentication

Resources

Official Documentation

• GitHub: https://github.com/vercel-labs/agent-browser
• AGENTS.md: AI agent integration guide
• Source Code: Available in opensrc/ directory

Environment Variables

AGENT_BROWSER_SESSION           # Default session name
AGENT_BROWSER_EXECUTABLE_PATH   # Custom browser binary
AGENT_BROWSER_EXTENSIONS        # Comma-separated extension paths
AGENT_BROWSER_PROVIDER          # Cloud provider (browseruse, browserbase)
AGENT_BROWSER_STREAM_PORT       # WebSocket port for streaming
AGENT_BROWSER_HOME              # Installation directory

Code Style Requirements

• No emojis in code, output, or documentation
• Unicode symbols acceptable: ✓, ✗, →, ⚠
• Use cli/src/color.rs for colored output (respects NO_COLOR)

Fetching Dependency Source

# npm packages
npx opensrc <package>

# Python packages
npx opensrc pypi:<package>

# Rust crates
npx opensrc crates:<package>

# GitHub repos
npx opensrc <owner>/<repo>

Quick Reference Card

# Navigate
agent-browser open <url>

# Analyze
agent-browser snapshot -i

# Interact
agent-browser click @e1
agent-browser fill @e2 "text"
agent-browser wait @e3

# Verify
agent-browser is visible @e1

# Capture
agent-browser screenshot page.png

# Semantic find
find role button click --name "Submit"

Best Practices:

1. Always snapshot -i before interacting
2. Use refs (@e1) for reliability
3. Wait strategically (--load networkidle, --url patterns)
4. Scope snapshots (-s selector) for large pages
5. Verify state (is visible, is enabled) before interaction
6. Use sessions (--session) for isolation
7. Save/load authentication state to avoid repetitive logins

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