Web Developer Tools by SessionManager.net

500+ Web development tools to inspect, debug, edit, test, optimize and audit websites. Privacy-first developer utility.

Available on Firefox for Android™

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About this extension

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.

Developer comments

Getting started
Click the toolbar icon (or press Alt+W) on any page. Tools are grouped by category on the left; use the search box to find any of the 550+ tools by name or keyword. Star a tool to add it to Favorites.

Permissions
The add-on asks for access to all websites because it is a general-purpose developer toolbox — every tool inspects or modifies the page you are currently on, and only when you activate it. Nothing runs in the background and no page data ever leaves your browser.

Not seeing a tool on a page?
Browser-internal pages (about:, addons.mozilla.org) and PDF viewers cannot be scripted by extensions. On other pages, reload the tab once after installing so the content script is loaded.

Free vs Pro
All core tools are free. Tools marked "PRO" are unlocked by an optional subscription — details at https://webdevelopertools.dev/pricing

Feedback & support
Use the feedback button inside the popup, or https://webdevelopertools.dev/contact

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Web Developer Tools by SessionManager.net

Required permissions:

Optional permissions:

Data collection:

Optional data collection, according to the developer: