Imported from justfinethanku/cc_chrome_devtools_mcp_skill (SKILL.md). Install upstream with npx skills add justfinethanku/cc_chrome_devtools_mcp_skill. Copyright stays with the author.

Chrome DevTools Testing Skill

Overview

This skill enables automated Chrome browser testing and performance analysis using the Chrome DevTools Protocol (CDP) via the chrome-devtools-mcp server. It provides access to 27 professional-grade tools for web application testing, performance measurement, accessibility validation, and browser automation.

Key capabilities:

• Performance analysis with Core Web Vitals (INP, LCP, CLS)
• Network monitoring and HAR export
• Accessibility tree inspection
• Responsive design testing
• Browser automation (form filling, navigation, interaction)
• Multi-tab and frame management
• Device and network condition emulation

Browser support: Chrome/Chromium only (stable, beta, dev, canary channels)

Node.js requirement: v20.19 or newer

Quick Start

Installation

# Add to Claude Code via CLI
claude mcp add chrome-devtools npx chrome-devtools-mcp@latest

# Verify installation
claude mcp list

Basic configuration

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": [
        "chrome-devtools-mcp@latest",
        "--isolated=true",
        "--viewport=1920x1080"
      ]
    }
  }
}

Important notes

• Browser auto-starts on first tool use (not on MCP connection)
• Use --isolated=true for security (creates temporary user data directories that auto-cleanup)
• Default behavior shares user data directory across sessions and does NOT clear between runs
• All browser content is exposed to MCP clients - avoid sensitive data

Current Core Web Vitals (as of March 12, 2024)

Three official metrics measured at 75th percentile of page loads:

1. Interaction to Next Paint (INP) - Replaced FID on March 12, 2024

   • Good: ≤ 200ms
   • Measures: Input delay + processing time + presentation delay
   • Requires: Real user interactions (field data only)

2. Largest Contentful Paint (LCP)

   • Good: ≤ 2.5 seconds
   • Measures: Main content loading performance

3. Cumulative Layout Shift (CLS)

   • Good: ≤ 0.1
   • Measures: Visual stability

Total Blocking Time (TBT) is NOT a Core Web Vital - it's a lab proxy metric for INP.

Common Use Cases

1. Performance Testing Workflow

Measure Core Web Vitals and analyze performance bottlenecks:

1. Start performance trace: performance_start_trace
2. Navigate to target URL: navigate_page
3. Wait for page load: wait_for
4. Stop trace and get metrics: performance_stop_trace
5. Analyze specific insights: performance_analyze_insight

Metrics captured:

• INP (Interaction to Next Paint)
• LCP (Largest Contentful Paint) with breakdown
• CLS (Cumulative Layout Shift)
• TBT (Total Blocking Time - lab proxy)
• Document latency analysis

Example:

performance_start_trace with reload=true, autoStop=false
wait_for page to stabilize
performance_stop_trace
performance_analyze_insight with insightName="LCPBreakdown"

2. Network Monitoring and HAR Export

Capture all HTTP requests/responses with timing details:

1. Navigate to URL: navigate_page
2. List all network requests: list_network_requests
3. Get specific request details: get_network_request

Captured data:

• Headers, bodies, cookies
• Timing (DNS, connect, SSL, wait, receive)
• Resource types (document, stylesheet, image, script, xhr, fetch)
• Security details (protocol, cipher suite)

Export as HAR: Use list_network_requests to generate HTTP Archive v1.2 format

Filter requests:

list_network_requests with resourceTypes=["xhr", "fetch", "document"]
list_network_requests with pageSize=50, pageIdx=0

3. Accessibility Validation

Inspect accessibility tree for WCAG compliance:

1. Navigate to page: navigate_page
2. Take accessibility snapshot: take_snapshot
3. Interact with elements using UIDs

Snapshot provides:

• Unique element identifiers (UIDs)
• Accessibility roles, names, properties
• ARIA attributes and computed roles
• Screen reader compatibility analysis
• Semantic structure validation

Example workflow:

take_snapshot verbose=false (returns text-based a11y tree)
# Identify element UIDs from snapshot
click uid="element-123"
fill uid="input-456" value="test data"

4. Responsive Design Testing

Test across devices and network conditions:

1. Resize viewport: resize_page width=375 height=667
2. Emulate network: emulate_network throttlingOption="Slow 3G"
3. Emulate CPU: emulate_cpu throttlingRate=4
4. Take screenshot: take_screenshot fullPage=true

Device emulation options:

• Viewport dimensions and device scale factor
• Network conditions: Offline, Slow 3G, Fast 3G, Slow 4G, Fast 4G
• CPU throttling: 1-20x slowdown
• Touch emulation with max touch points

Screenshot formats: PNG, JPEG, WebP (with quality settings)

5. Browser Automation

Automated form filling, navigation, and interaction:

1. Take snapshot to get element UIDs: take_snapshot
2. Fill form fields: fill_form elements=[{uid, value}, ...]
3. Click buttons: click uid="submit-button"
4. Handle dialogs: handle_dialog action="accept"
5. Wait for results: wait_for text="Success"

Interaction tools:

• click (single/double-click)
• fill (input fields, textareas, selects)
• fill_form (multiple fields at once)
• hover (mouse hover)
• drag (drag-and-drop)
• upload_file (file inputs)
• handle_dialog (alerts, confirms, prompts)

Navigation tools:

• navigate_page (URLs, reload)
• navigate_page_history (back/forward)
• wait_for (text appearance, conditions)

6. Multi-Tab Management

Work with multiple pages and frames:

1. List open pages: list_pages
2. Create new page: new_page url="https://example.com"
3. Switch context: select_page pageIdx=1
4. Close pages: close_page pageIdx=2

Frame handling:

• Automatic attachment to child frames and workers
• Frame tree structure inspection
• Session persistence across navigation

Advanced Workflows

Performance Analysis with Device Emulation

1. resize_page width=390 height=844 (iPhone 14 Pro)
2. emulate_network throttlingOption="Fast 4G"
3. emulate_cpu throttlingRate=4
4. performance_start_trace reload=true
5. performance_stop_trace
6. performance_analyze_insight insightName="DocumentLatency"

Network Analysis with Filtering

1. navigate_page url="https://example.com"
2. list_network_requests resourceTypes=["script", "fetch", "xhr"]
3. Filter by: pageSize=100, pageIdx=0, includePreservedRequests=true
4. get_network_request reqid=123 (detailed timing/headers/body)

Accessibility Testing Pattern

1. navigate_page url="https://example.com"
2. take_snapshot verbose=true (full a11y tree with all properties)
3. Validate: roles, names, ARIA attributes, relationships
4. Test interactions: click, fill, keyboard navigation via UIDs

Cross-Browser Viewport Testing

1. Define breakpoints: [320, 768, 1024, 1920]
2. For each breakpoint:
   - resize_page width=X height=Y
   - take_screenshot format="png" quality=90
   - take_snapshot (verify accessibility)
3. Compare layouts and a11y across sizes

Complete Tool Reference

27 tools available across 6 categories:

Input automation (8): click, drag, fill, fill_form, handle_dialog, hover, press_key, upload_file

Navigation (7): close_page, list_pages, navigate_page, navigate_page_history, new_page, select_page, wait_for

Emulation (3): emulate_cpu, emulate_network, resize_page

Performance (3): performance_analyze_insight, performance_start_trace, performance_stop_trace

Network (2): get_network_request, list_network_requests

Debugging (4): evaluate_script, get_console_message, list_console_messages, take_screenshot, take_snapshot

For detailed tool parameters and examples, see TOOLS.md

For complete workflow patterns, see WORKFLOWS.md

For Core Web Vitals thresholds and measurement guide, see METRICS.md

Configuration Options

Connection flags

• --browserUrl, -u <string> - Connect to running Chrome instance (port forwarding)
• --wsEndpoint, -w <string> - WebSocket endpoint for Chrome connection
• --wsHeaders <JSON> - Custom headers for authenticated WebSocket connections

Browser configuration

• --headless <boolean> - Run in headless mode (default: false)
• --executablePath, -e <string> - Path to custom Chrome executable
• --channel <string> - Chrome channel: stable, canary, beta, dev (default: stable)
• --viewport <string> - Initial viewport size (format: WIDTHxHEIGHT, e.g., 1280x720)

Security and isolation

• --isolated <boolean> - RECOMMENDED: Creates temporary user-data-dir, auto-cleanup (default: false)
• --user-data-dir <string> - Custom user data directory
• --acceptInsecureCerts <boolean> - Ignore certificate errors (SECURITY RISK - dev/test only)

Network

• --proxyServer <string> - Proxy server configuration

Debugging

• --logFile <string> - Path for debug logs (set DEBUG=* env var for verbose logs)

Additional

• --chromeArg <string> - Additional Chrome arguments (repeatable)

View all options: npx chrome-devtools-mcp@latest --help

Production Configuration Examples

Secure isolated testing

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": [
        "chrome-devtools-mcp@latest",
        "--isolated=true",
        "--headless=true",
        "--viewport=1920x1080",
        "--channel=stable"
      ]
    }
  }
}

Connect to external Chrome instance

# Launch Chrome with remote debugging
google-chrome --remote-debugging-port=9222 --user-data-dir=/tmp/chrome-profile

# Get WebSocket endpoint
curl http://127.0.0.1:9222/json/version | jq -r '.webSocketDebuggerUrl'

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": [
        "chrome-devtools-mcp@latest",
        "--wsEndpoint=ws://127.0.0.1:9222/devtools/browser/<id>"
      ]
    }
  }
}

Production with logging

{
  "mcpServers": {
    "chrome-devtools-prod": {
      "command": "npx",
      "args": [
        "chrome-devtools-mcp@latest",
        "--browserUrl=http://127.0.0.1:9222",
        "--isolated=true",
        "--logFile=/var/log/chrome-devtools-mcp.log"
      ],
      "env": {
        "DEBUG": "*"
      }
    }
  }
}

Security Considerations

Data exposure warning

Official Chrome DevTools MCP security notice:

"chrome-devtools-mcp exposes content of the browser instance to the MCP clients allowing them to inspect, debug, and modify any data in the browser or DevTools. Avoid sharing sensitive or personal information that you don't want to share with MCP clients."

Best practices

1. Use isolated mode for sensitive workflows

   • --isolated=true creates temporary user data directories
   • Automatically cleaned after browser closes
   • Prevents data persistence between sessions

2. Certificate handling caution

   • --acceptInsecureCerts is a security risk
   • Only use in development/testing environments
   • Never use with sensitive data

3. User data directory management

   • Default directory shared across all instances
   • Not cleared between runs
   • Contains cookies, cache, browsing history
   • Use --isolated or custom --user-data-dir for control

4. WebSocket authentication

   • Use --wsHeaders for authenticated connections
   • Example: --wsHeaders='{"Authorization":"Bearer token"}'
   • Only works with --wsEndpoint

Technical Constraints

Verified limitations

1. Browser support: Chrome/Chromium only (no Firefox, Safari, Edge legacy)

2. Node.js requirement: v20.19 or newer (latest maintenance LTS)

3. Browser lifecycle: Browser auto-starts on first tool use, NOT on MCP server connection

4. Default persistence: User data directory persists between runs unless --isolated=true is used

5. Permission requirements:

   • macOS Full Disk Access may be required for some MCP clients
   • Chrome needs permission to create its own sandboxes
   • May need to disable MCP client sandboxing or use external Chrome instance

6. Screenshot formats: Specified format (JPEG/PNG) for initial capture, final output uses WebP with PNG fallback

7. Tool availability: All 27 tools available immediately after connection; no progressive unlocking

Resources and Documentation

Official sources

• GitHub Repository: https://github.com/ChromeDevTools/chrome-devtools-mcp
• npm Package: https://www.npmjs.com/package/chrome-devtools-mcp
• Chrome DevTools Protocol: https://chromedevtools.github.io/devtools-protocol/

Core Web Vitals

• Web Vitals Overview: https://web.dev/articles/vitals
• INP Documentation: https://web.dev/articles/inp
• LCP Documentation: https://web.dev/articles/lcp
• CLS Documentation: https://web.dev/articles/cls
• INP Replacing FID (March 12): https://web.dev/blog/inp-cwv-march-12

Tools

• PageSpeed Insights: https://pagespeed.web.dev
• Chrome User Experience Report: https://developer.chrome.com/docs/crux
• Lighthouse Documentation: https://developer.chrome.com/docs/lighthouse

Related Skill Files

• WORKFLOWS.md - Detailed workflow patterns and multi-step processes
• METRICS.md - Complete Core Web Vitals thresholds and measurement guide
• TOOLS.md - Comprehensive tool parameter reference and examples

Version Information

• MCP Server Version: v0.5.1 (October 17, 2025)
• Tool Count: 27 tools
• Core Web Vitals Update: INP replaced FID on March 12, 2024
• Current Metrics: INP, LCP, CLS (TBT is lab proxy, not Core Web Vital)