Browser Dev Tools

Overview

This skill provides Chrome DevTools Protocol tools for validating and debugging browser-rendered artifacts during development. Use these tools to verify that localhost servers are rendering correctly and to debug visual issues proactively.

The tools connect to Chrome running on port :9222 with remote debugging enabled.

When to Use This Skill

Use this skill proactively in these scenarios:

1. After making frontend code changes - Validate that React, Bun, HTML, or other frontend code renders correctly on localhost
2. After starting a dev server - Verify the application loads and displays properly
3. When debugging browser rendering issues - Inspect page state, DOM structure, or cookies
4. When validating UI changes - Take screenshots to visually confirm changes appear as expected

Important: Always use this skill proactively after completing frontend development tasks to validate the work before considering it done.

Available Tools

All browser tools are located in ~/.claude/skills/browser-dev-tools/tools/ and should be executed via the Bash tool.

Start Chrome

~/.claude/skills/browser-dev-tools/tools/browser-start.js                # Fresh profile
~/.claude/skills/browser-dev-tools/tools/browser-start.js --profile      # Auto-detect profile
~/.claude/skills/browser-dev-tools/tools/browser-start.js --profile "Profile 2"  # Specific profile

Launch Chrome with remote debugging.

Profile Auto-Detection:

• When using --profile without a profile name, the script automatically selects the appropriate Chrome profile based on the current working directory:
  • ~/personal/** → Uses Default profile (tnagengast@gmail.com)
  • ~/work/** → Uses Profile 1 (tom@cable.tech)
• You can override this by specifying a profile name: --profile "Profile 2"

Important: Always use --profile (auto-detect) or specify a profile when you need to preserve authentication state for testing authenticated pages.

Navigate

~/.claude/skills/browser-dev-tools/tools/browser-nav.js http://localhost:3000
~/.claude/skills/browser-dev-tools/tools/browser-nav.js http://localhost:3000 --new

Navigate to URLs. Use --new flag to open in a new tab instead of reusing the current tab.

Screenshot

~/.claude/skills/browser-dev-tools/tools/browser-screenshot.js

Capture the current viewport and return a temporary file path. Always take screenshots after navigating to validate the rendered output visually.

Evaluate JavaScript

~/.claude/skills/browser-dev-tools/tools/browser-eval.js 'document.title'
~/.claude/skills/browser-dev-tools/tools/browser-eval.js 'document.querySelectorAll("a").length'

Execute JavaScript in the active tab to extract data, inspect page state, or perform DOM operations programmatically.

Pick Elements

~/.claude/skills/browser-dev-tools/tools/browser-pick.js "Click the submit button"

Launch an interactive picker that lets the user click elements to select them. The user can select multiple elements (Cmd/Ctrl+Click) and press Enter when done. Returns CSS selectors for the selected elements.

Use this when the user wants to select specific DOM elements on the page.

Cookies

~/.claude/skills/browser-dev-tools/tools/browser-cookies.js

Display all cookies for the current tab including domain, path, httpOnly, and secure flags. Use this to debug authentication issues or inspect session state.

Common Workflows

Validating Frontend Changes (Primary Use Case)

After making changes to frontend code (React components, HTML, CSS, etc.):

1. Start Chrome if not already running:

   ~/.claude/skills/browser-dev-tools/tools/browser-start.js --profile  # Auto-detects profile
   

   Note: Use --profile to auto-detect the appropriate profile based on cwd (personal vs work).

2. Navigate to localhost:

   ~/.claude/skills/browser-dev-tools/tools/browser-nav.js http://localhost:PORT
   

   Replace PORT with the appropriate port (e.g., 3000, 5173, 8080).

3. Take a screenshot:

   ~/.claude/skills/browser-dev-tools/tools/browser-screenshot.js
   

4. Read the screenshot using the Read tool to visually validate the changes.

5. If issues are found, use JavaScript evaluation to inspect the page state:

   ~/.claude/skills/browser-dev-tools/tools/browser-eval.js 'document.body.innerHTML'
   

Debugging Rendering Issues

When troubleshooting why something isn't rendering correctly:

1. Navigate to the problematic page

2. Take a screenshot to see the current state

3. Evaluate JavaScript to inspect:

   • DOM structure: document.querySelector('#myElement')
   • Console errors: console.log(...)
   • Element properties: document.querySelector('#myElement').style

4. Check cookies if authentication or session issues are suspected

Best Practices

• Always validate proactively - Take screenshots after frontend changes to catch visual issues early
• Use profile auto-detection - Use --profile (without arguments) to automatically load the correct profile based on your working directory (personal vs work)
• Navigate before evaluating - Ensure the page is loaded before running JavaScript
• Read screenshots - Always use the Read tool on screenshot paths to view the captured image
• Check common ports - Typical dev servers run on 3000 (React/Next.js), 5173 (Vite), 8080 (generic), or 4200 (Angular)