Agent Browser

agent-browser CLI

A headless browser automation CLI designed for AI agents, with fast Rust-based execution and element refs optimized for LLM reasoning.

Overview

agent-browser provides programmatic browser control through a CLI that's purpose-built for AI agent workflows. It uses deterministic element references (@e1, @e2, etc.) from accessibility trees, making it ideal for LLM-based automation where consistent element targeting is critical.

Key Features:

• Fast Rust-based CLI with Node.js fallback
• Element refs (@e1, @e2) for stable LLM reasoning
• Session isolation for parallel browser instances
• JSON output for programmatic parsing
• Accessibility tree snapshots for element discovery
• CDP connection support for existing browser instances

When to Use

• Automating web interactions (form filling, clicking, navigation)
• Scraping web content with accessibility tree parsing
• Testing web applications programmatically
• Multi-agent scenarios requiring isolated browser sessions
• Screenshot capture and PDF generation
• Monitoring web page state changes

Prerequisites

• Node.js >= 18 or Bun runtime
• Chromium (installed via agent-browser install)

Installation

# Install globally
bun install -g agent-browser

# Download Chromium
agent-browser install

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

Verify installation:

agent-browser --version

Quick Start

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

# Get accessibility snapshot with element refs
agent-browser snapshot -i  # -i = interactive elements only

# Click an element by ref
agent-browser click @e2

# Fill a form field
agent-browser fill @e3 "test@example.com"

# Take a screenshot
agent-browser screenshot output.png

Core Workflow

1. Open Page and Snapshot

# Open URL
agent-browser open https://example.com

# Get interactive elements with refs
agent-browser snapshot -i --json

The snapshot returns elements like:

@e1 link "Home"
@e2 textbox "Email"
@e3 button "Submit"

2. Interact Using Refs

# Click by ref
agent-browser click @e2

# Type into focused element
agent-browser type @e2 "hello@example.com"

# Fill (clears first, then types)
agent-browser fill @e2 "hello@example.com"

# Press keyboard key
agent-browser press Enter

3. Verify State

# Check element visibility
agent-browser is visible @e3

# Get element text
agent-browser get text @e1

# Get page URL
agent-browser get url

Command Reference

Navigation

Interactions

Information

State Checks

Find Elements

# Find by role and click
agent-browser find role button click --name Submit

# Find by text
agent-browser find text "Sign In" click

# Find by label
agent-browser find label "Email" fill "test@example.com"

# Find by placeholder
agent-browser find placeholder "Search..." type "query"

Session Management

Sessions provide isolated browser instances for parallel execution:

# Use named session
agent-browser --session login-flow open https://app.com

# Different session for another task
agent-browser --session checkout open https://app.com/cart

# List active sessions
agent-browser session list

# Environment variable (persistent across commands)
export AGENT_BROWSER_SESSION=my-session
agent-browser open https://example.com

JSON Output

Use --json for machine-readable output:

# Snapshot as JSON
agent-browser snapshot -i --json

# Get element info as JSON
agent-browser get text @e1 --json

# Parse in scripts
agent-browser get url --json | jq -r '.url'

Common Pitfalls

This section covers frequent failure modes and how to debug them. Each pitfall includes the symptom you'll see, the underlying cause, and the fix.

Browser not found

Symptom: Error: Browser executable not found at default path or agent-browser: command not found

Cause: Chromium isn't installed, or agent-browser CLI isn't on PATH

Fix:

# Install Chromium
agent-browser install

# For Linux, install system dependencies
agent-browser install --with-deps

# Verify installation
agent-browser --version

Element ref becomes stale after page change

Symptom: Error: Element @e2 not found even though you just used it, or clicks fail silently

Cause: Element refs change when the DOM updates (navigation, page reload, dynamic content). Refs are only valid for the current DOM snapshot.

Fix:

# Always re-snapshot after major page changes
agent-browser click @e1  # Click submit
agent-browser wait 2000  # Wait for navigation
agent-browser snapshot -i --json  # Get fresh refs
agent-browser click @e1  # Use new ref (was @e1 before? Verify!)

Prevention: In scripts, capture fresh refs after each navigation or dynamic load.

Session conflicts and port binding

Symptom: Error: Session "default" already in use or Port 9222 already in use

Cause: Browser session is still running from a previous command or crashed script, preventing a new session from starting

Fix:

# List active sessions
agent-browser session list

# Kill a specific session
agent-browser session kill my-session

# Use unique session names to avoid conflicts
agent-browser --session upload-$(date +%s) open https://app.com

# Or set environment variable once
export AGENT_BROWSER_SESSION=task-$(date +%s)
agent-browser open https://example.com
agent-browser close

Clicks and interactions don't work on hidden elements

Symptom: agent-browser click @e5 succeeds but nothing happens, or element is invisible in screenshot

Cause: Element is outside viewport, hidden by CSS (display: none, visibility: hidden), or covered by another element. Accessibility tree may show it, but browser can't interact with it.

Fix:

# Check visibility before interaction
agent-browser is visible @e5

# Scroll to make element visible
agent-browser scroll down 500

# Take screenshot to visually verify
agent-browser screenshot current-state.png

# Try parent element if child is deeply nested
agent-browser click @e4  # Click parent button instead

Prevention: Always take screenshots before and after critical interactions to verify visual state.

Timeout waiting for navigation or element

Symptom: Error: Timeout waiting for element or script hangs indefinitely after clicking a link

Cause:

• Element doesn't exist or appears after longer than expected delay
• Navigation is stuck (network error, page not loading)
• Element selector is wrong

Fix:

# Explicit wait before checking for element
agent-browser wait 2000  # Wait 2 seconds
agent-browser snapshot -i --json  # Check if element exists

# Wait for specific element to appear
agent-browser wait @e3

# Increase timeout with explicit waits in script
agent-browser click @submit
sleep 3  # Shell script sleep
agent-browser snapshot -i

# Check page title to verify navigation worked
agent-browser get title

Prevention: Add explicit wait commands after form submissions or link clicks that cause navigation.

Snapshot is empty or missing expected elements

Symptom: agent-browser snapshot -i --json returns [] or very few elements, but you see them visually in screenshot

Cause:

• Page content is rendered by JavaScript (React, Vue, etc.) that hasn't completed
• Elements lack accessible labels or roles
• -i flag filters too aggressively

Fix:

# Wait for content to render
agent-browser wait 2000
agent-browser snapshot -i

# Remove interactive-only filter to see all elements
agent-browser snapshot -c  # Compact but includes all elements

# Increase tree depth to find nested elements
agent-browser snapshot -d 5

# Use full snapshot to diagnose
agent-browser snapshot --json | jq . | less

# Check page title to verify page loaded
agent-browser get title

Prevention: Add wait delays after opening pages with heavy JavaScript rendering.

Form fill doesn't work or text is partial

Symptom: Text appears to be cut off, only first few characters typed, or field stays empty

Cause:

• Field wasn't focused before typing (race condition)
• Field has input validation or character limit
• JavaScript event handlers expect specific typing speed or blur event

Fix:

# Always focus explicitly before filling
agent-browser focus @e2
agent-browser wait 500  # Let field settle
agent-browser fill @e2 "complete@example.com"

# For fields with slow JS event handling
agent-browser type @e2 "first part"
agent-browser wait 500
agent-browser type @e2 "second part"

# Verify what was actually entered
agent-browser get value @e2

Prevention: After any form fill, immediately verify the value was entered correctly with get value.

Network requests fail or external API timeouts

Symptom: Page loads but data doesn't populate, or integration tests fail when hitting real APIs

Cause:

• External API is slow or unreachable
• CORS errors (browser blocks requests to different domain)
• Missing authentication headers
• Network is isolated (testing environment)

Fix:

# Set custom headers for auth
agent-browser --headers '{"Authorization": "Bearer token123"}' open https://api.example.com

# Mock API responses instead
agent-browser network route "**/api/data" --body '{"result":"mocked"}'

# Add explicit wait for API response
agent-browser wait 3000  # Give API time to respond
agent-browser snapshot -i

# Fallback: Use `--headed` to see error messages
agent-browser --headed open https://app.com
agent-browser click @e1  # See browser console errors

Prevention: For testing, use network route to mock external APIs. For production, verify connectivity before running automation.

Browser crashes or becomes unresponsive

Symptom: agent-browser command hangs or process crashes with segmentation fault; Chrome window closes unexpectedly

Cause:

• Out of memory (too many long-running sessions or screenshots)
• Invalid CDP connection
• Rare Chromium/Playwright crash
• Insufficient system resources

Fix:

# Restart with fresh session
agent-browser session kill all-sessions  # Or specify a name

# Use lightweight mode with limited resources
agent-browser --session lite open https://minimal-site.com

# Reduce screenshot frequency
# Instead of: agent-browser screenshot after every click
# Do: agent-browser screenshot only on failure

# Check system resources
top -n 1 | head -20

# Run with --debug for crash diagnostics
agent-browser --debug open https://example.com 2>&1 | tail -50

Prevention:

• Close sessions explicitly: agent-browser close
• Use unique session names for long-lived tasks
• Monitor memory in long automation scripts

Element ref is ambiguous (@e1 appears for multiple elements)

Symptom: Multiple elements resolve to the same @e number, clicking @e1 affects the wrong element

Cause: Accessibility tree groups similar elements (buttons, links) and agent-browser assigns refs based on order, not uniqueness

Fix:

# Use full snapshot to understand structure
agent-browser snapshot -d 3 --json > structure.json
cat structure.json | jq .  # Examine hierarchy

# Click using find by text if available
agent-browser find text "Specific Button Text" click

# Use CSS selector if accessibility tree isn't clear
agent-browser find selector "button.submit-btn" click

# Take screenshot and count visually
agent-browser screenshot debug.png
# Then manually map which @eN corresponds to which button

# Use context to disambiguate
agent-browser get text @e1  # Check what @e1 actually is

Prevention: Always verify element identity by checking its text or taking screenshots before critical interactions.

Advanced Features

CDP Connection

Connect to an existing Chrome instance:

# Start Chrome with debugging
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --remote-debugging-port=9222

# Connect agent-browser
agent-browser --cdp 9222 snapshot

Video Recording

# Start recording
agent-browser record start recording.webm https://example.com

# Perform actions...
agent-browser click @e1
agent-browser fill @e2 "test"

# Stop and save
agent-browser record stop

Network Interception

# Block requests to URL pattern
agent-browser network route "**/analytics/*" --abort

# Mock API response
agent-browser network route "**/api/user" --body '{"name": "Test"}'

# View captured requests
agent-browser network requests

Custom Headers

# Set auth headers
agent-browser --headers '{"Authorization": "Bearer token123"}' open https://api.example.com

Browser Extensions

# Load extension
agent-browser --extension /path/to/extension open https://example.com

AI Agent Patterns

Form Automation

#!/bin/bash
# Login automation script

agent-browser open https://app.com/login

# Get form elements
agent-browser snapshot -i --json > elements.json

# Fill credentials
agent-browser fill @e2 "user@example.com"
agent-browser fill @e3 "password123"

# Submit
agent-browser click @e4

# Wait for navigation
agent-browser wait 2000

# Verify login
agent-browser get url --json | jq -r '.url'

Data Extraction

#!/bin/bash
# Scrape product data

agent-browser open https://shop.com/products

# Get page content
agent-browser snapshot --json > snapshot.json

# Extract specific element text
agent-browser get text '[data-testid="price"]' --json

# Screenshot for verification
agent-browser screenshot products.png

Multi-Page Workflow

#!/bin/bash
SESSION="checkout-flow"

# Step 1: Add to cart
agent-browser --session $SESSION open https://shop.com/product/123
agent-browser --session $SESSION click @add-to-cart-button
agent-browser --session $SESSION wait 1000

# Step 2: Go to checkout
agent-browser --session $SESSION open https://shop.com/checkout
agent-browser --session $SESSION snapshot -i

# Step 3: Fill shipping
agent-browser --session $SESSION fill @shipping-name "John Doe"
agent-browser --session $SESSION fill @shipping-address "123 Main St"

# Cleanup
agent-browser --session $SESSION close

Options Reference

Environment Variables

Examples

Example 1: Simple Web Scraping

User request:

"Scrape the product title and price from https://example.com/product/123"

Workflow:

# 1. Navigate to page
agent-browser open https://example.com/product/123

# 2. Get accessibility snapshot
agent-browser snapshot -i --json > page.json

# 3. Identify elements (example output):
# @e5 heading "Premium Widget Pro"
# @e12 text "$49.99"

# 4. Extract data
agent-browser get text @e5 --json  # Returns: {"text": "Premium Widget Pro"}
agent-browser get text @e12 --json  # Returns: {"text": "$49.99"}

Expected output:

{
  "title": "Premium Widget Pro",
  "price": "$49.99"
}

Time: 2-3 seconds

Example 2: Form Submission with Verification

User request:

"Fill out the contact form at https://example.com/contact and verify submission"

Workflow:

# 1. Navigate and snapshot
agent-browser open https://example.com/contact
agent-browser snapshot -i

# Example snapshot output:
# @e1 textbox "Name"
# @e2 textbox "Email"
# @e3 textbox "Message"
# @e4 button "Send"

# 2. Fill form fields
agent-browser fill @e1 "John Doe"
agent-browser fill @e2 "john@example.com"
agent-browser fill @e3 "I have a question about your product"

# 3. Submit
agent-browser click @e4

# 4. Wait for response
agent-browser wait 2000

# 5. Verify success
agent-browser snapshot -i | grep "Thank you"
# Or take screenshot for manual verification
agent-browser screenshot success.png

Expected outcome:

• Form submitted successfully
• Page shows confirmation message
• Screenshot saved showing success state

Time: 4-6 seconds

Example 3: Multi-Page Workflow with Session

User request:

"Add item to cart, proceed to checkout, and fill shipping info"

Workflow:

# Use session for state persistence across commands
SESSION="checkout-flow-$(date +%s)"

# 1. Add to cart
agent-browser --session $SESSION open https://shop.example.com/product/widget
agent-browser --session $SESSION snapshot -i | grep "Add to Cart"
agent-browser --session $SESSION click @add-to-cart  # Assuming @add-to-cart ref found
agent-browser --session $SESSION wait 1000  # Wait for cart update

# 2. Go to checkout
agent-browser --session $SESSION open https://shop.example.com/checkout
agent-browser --session $SESSION snapshot -i

# 3. Fill shipping form (refs from snapshot)
agent-browser --session $SESSION fill @shipping-name "Jane Smith"
agent-browser --session $SESSION fill @shipping-address "456 Oak Ave"
agent-browser --session $SESSION fill @shipping-city "Portland"
agent-browser --session $SESSION select @shipping-state "OR"
agent-browser --session $SESSION fill @shipping-zip "97201"

# 4. Take screenshot before submission
agent-browser --session $SESSION screenshot checkout-filled.png

# 5. Cleanup
agent-browser --session $SESSION close

Expected outcome:

• Item added to cart successfully
• Checkout form filled with shipping details
• Screenshot saved showing completed form
• Session cleaned up

Time: 8-12 seconds

Example 4: Login and Data Extraction

User request:

"Log into dashboard, navigate to reports, and extract table data"

Workflow:

SESSION="dashboard-scrape"

# 1. Login
agent-browser --session $SESSION open https://app.example.com/login
agent-browser --session $SESSION snapshot -i

# Fill login form
agent-browser --session $SESSION fill @email "user@example.com"
agent-browser --session $SESSION fill @password "secretpass"
agent-browser --session $SESSION click @submit
agent-browser --session $SESSION wait 2000

# 2. Navigate to reports
agent-browser --session $SESSION open https://app.example.com/reports
agent-browser --session $SESSION wait 1000

# 3. Extract table data
agent-browser --session $SESSION snapshot --json > reports.json

# Parse JSON to extract table rows
# @e20 table
#   @e21 row "Q1 2024, $50,000, 15% growth"
#   @e22 row "Q2 2024, $62,000, 24% growth"

agent-browser --session $SESSION get text @e20 --json

# 4. Cleanup
agent-browser --session $SESSION close

Expected output:

{
  "reports": [
    {"quarter": "Q1 2024", "revenue": "$50,000", "growth": "15%"},
    {"quarter": "Q2 2024", "revenue": "$62,000", "growth": "24%"}
  ]
}

Time: 6-10 seconds

Troubleshooting

Issue: Element Reference Not Found

Symptoms:

Error: Element @e5 not found

Cause: Element ref changed after page update or snapshot was stale

Solution:

# 1. Get fresh snapshot
agent-browser snapshot -i

# 2. Verify element ref in output
# Look for expected element in snapshot output

# 3. If element doesn't appear, try without -i flag
agent-browser snapshot  # Shows all elements, not just interactive

# 4. If still missing, check if page loaded completely
agent-browser wait 2000  # Wait for page to settle
agent-browser snapshot -i

Issue: Timeout Waiting for Navigation

Symptoms:

Error: Navigation timeout after 30000ms

Cause: Page takes too long to load or network issues

Solution:

# 1. Check if page is accessible
agent-browser --headed open https://example.com  # Visual debugging

# 2. Increase wait time after navigation
agent-browser open https://slow-site.com
agent-browser wait 5000  # Wait 5 seconds

# 3. Check network requests
agent-browser network requests  # See what's loading

# 4. Use CDP connection for better control
agent-browser --cdp 9222 open https://example.com

Issue: Click Not Working

Symptoms: Element click command runs but nothing happens

Cause: Element not visible, disabled, or covered by another element

Solution:

# 1. Check if element is visible
agent-browser is visible @e3
# Returns: true/false

# 2. Check if element is enabled
agent-browser is enabled @e3

# 3. Try scrolling to element first
agent-browser scroll down 500
agent-browser wait 500
agent-browser click @e3

# 4. Take screenshot to see page state
agent-browser screenshot debug.png

# 5. Try double-click instead
agent-browser dblclick @e3

Issue: Form Input Not Registering

Symptoms: Text typed but form field remains empty

Cause: JavaScript framework requires special events or delays

Solution:

# 1. Focus element first
agent-browser focus @e2
agent-browser wait 200

# 2. Use fill instead of type (clears first)
agent-browser fill @e2 "text content"

# 3. Add delays between keystrokes
agent-browser type @e2 "slow"
agent-browser wait 100

# 4. Try pressing Tab after filling to trigger validation
agent-browser fill @e2 "email@example.com"
agent-browser press Tab

Issue: Session Persistence Problems

Symptoms: Previous session state not available

Cause: Session wasn't properly named or browser closed unexpectedly

Solution:

# 1. Always use explicit session names
SESSION="my-workflow-$(date +%s)"  # Unique session ID
agent-browser --session $SESSION open https://example.com

# 2. Check active sessions
agent-browser --session $SESSION get url
# If error, session doesn't exist

# 3. Don't reuse session names across runs
# Each workflow should have unique session ID

# 4. Cleanup sessions when done
agent-browser --session $SESSION close

Issue: Chromium Installation Failed

Symptoms:

Error: Failed to download Chromium

Cause: Network issues, disk space, or missing system dependencies

Solution:

# 1. Check disk space
df -h  # Ensure >2GB free

# 2. Retry installation with verbose output
agent-browser install --debug

# 3. On Linux, install system dependencies first
agent-browser install --with-deps

# 4. Use custom browser if needed
agent-browser --executable-path /usr/bin/chromium open https://example.com

# 5. Verify installation
agent-browser --version
ls ~/.cache/ms-playwright/  # Check if Chromium exists

Issue: JSON Output Malformed

Symptoms: Can't parse JSON output from commands

Cause: Mixed text/JSON output or errors in JSON mode

Solution:

# 1. Use --json flag consistently
agent-browser get text @e5 --json  # Not: agent-browser get text @e5

# 2. Redirect stderr to separate stream
agent-browser snapshot --json 2>errors.log >output.json

# 3. Validate JSON output
agent-browser snapshot --json | jq .  # Will error if invalid

# 4. Check for error messages in output
agent-browser snapshot --json | grep -E '^{' | jq .

Best Practices

• Always snapshot first: Get element refs before interacting
• Use --json for parsing: Machine-readable output for scripts
• Session isolation: Use --session for parallel workflows
• Explicit waits: Add wait commands after navigation/clicks
• Interactive snapshots: Use -i flag to reduce noise
• Verify state: Check element visibility before clicking
• Screenshot on failure: Capture state when automation fails

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