Web Developer Tools

Web Developer Tools is a modern, privacy-first toolbox for web developers, frontend engineers, designers, QA testers, accessibility specialists and SEO professionals. Inspect, debug, edit, test, optimize and audit any website without leaving Firefox.

550+ developer tools, organized into clear categories:

• 🔍 HTML & DOM inspection and debugging
• 🎨 CSS inspection, visualization and live editing
• ⚙ JavaScript debugging, console capture and page analysis
• 🌐 Network, request header and resource inspection
• 💾 Storage, Cookies, Cache & IndexedDB managers
• 📈 SEO auditing and metadata analysis
• ♿ Accessibility (WCAG) inspection
• ⚡ Performance and Core Web Vitals analysis
• 🔒 Security header and HTTPS inspection
• 🖼 Image, Form and Responsive Design utilities
• 📱 PWA inspection and manifest validation
• 🧩 Technology detection
• 🎯 Color, typography and design tools
• 📄 Data formatting, generators and validators
• 🖥 Browser environment and page utilities

🔒 Privacy first

Every tool runs entirely on-device: the page data the tools read — DOM, CSS, cookies, headers, storage — is shown to you in your own browser and is never uploaded to us. We do not collect browsing history, keystrokes, analytics or telemetry of any kind. The extension contacts our servers only for the two things you choose to use: optional account sign-in (used solely to manage a Pro subscription) and the built-in feedback form, which sends only the message you write and the email address you optionally provide.

✨ Why you'll love it

• 550+ organized developer tools in one extension
• Privacy-first — no unnecessary data collection
• Fast, lightweight and easy to use
• Works on virtually any website
• Available in 11 languages
• Powerful free features with optional Pro upgrades

Whether you're debugging layouts, inspecting HTML and CSS, auditing SEO, testing accessibility, analyzing performance or managing browser storage, Web Developer Tools provides everything you need in one place.