Browser Extensions & DevTools

One tool for intercepting, mocking, and replaying HTTP — acquired by BrowserStack

Requestly is an open-source HTTP interceptor, API client, and session replay tool that lets developers modify, mock, and debug network traffic without leaving the browser. Acquired by BrowserStack and trusted by 200,000+ developers, it bundles a Chrome extension, a full API client, mock servers, and shareable session captures into one free-plus-commercial product.

Visualize JSON, YAML, XML, and CSV as interactive graphs

JSON Crack transforms structured data files into interactive, visual graphs that make complex nested data easy to understand. Paste or import JSON, YAML, XML, CSV, or TOML and instantly see the data as a navigable node graph with collapsible sections, search, and path highlighting. All processing happens client-side with no server storage.

In-page AI browser agent via a single script tag

Page Agent is Alibaba's open-source JavaScript library that embeds an AI GUI agent directly into any web page through a single script tag injection. Unlike headless browser tools that operate externally, Page Agent works inside the DOM using text-based manipulation for natural language QA testing, enterprise copilots, and making legacy web apps AI-native. It supports BYOLLM with any model provider and requires no backend changes.

Google Chrome Labs visual design tool for editing live web pages

VisBug is a Chrome Labs browser extension that lets developers and designers edit live web pages visually. It provides tools for moving, resizing, and styling elements directly on the page with point-and-click interaction. Features include margin and padding visualization, typography editing, color modification, and accessibility inspection without touching code or opening DevTools.

All-in-one browser DevTools extension for web developers

Hoverify is a browser extension that consolidates essential web development tools into a single overlay interface. It provides element inspection with CSS details, responsive design testing, accessibility checking, color picking, screenshot capture, and asset downloading. Activated by hovering over any webpage element, it provides instant development context without opening browser DevTools.

Browser automation CLI built for AI agents by Vercel Labs

Agent Browser is a Rust-based browser automation CLI designed specifically for AI agent workflows rather than traditional testing. Developed by Vercel Labs, it provides semantic element selection through a refs system, accessibility tree snapshots, session persistence, and authentication vaults. Unlike Playwright or Puppeteer which target test automation, Agent Browser optimizes for token efficiency and deterministic element selection that gives LLMs reliable browser interaction capabilities.

Browser-native frontend coding agent for production codebases

Stagewise is an open-source frontend coding agent with 6,500+ GitHub stars that runs directly in the browser on localhost. YC S25 backed, it lets developers and designers point-and-prompt on live web applications with full devtools and console access, bridging the gap between visual editing and production codebase modification.

AI-powered vision-driven UI automation for web, Android, and iOS

Midscene.js is an open-source UI automation framework from ByteDance's Web Infra team that uses vision-based AI models to understand and interact with interfaces. It replaces fragile CSS selectors with natural language descriptions, supporting web browsers via Playwright and Puppeteer, Android via ADB, and iOS via WebDriverAgent from a unified JavaScript SDK.

Scalable browser infrastructure for AI agents

Hyperbrowser is a YC S24-backed cloud browser platform purpose-built for AI agent automation at scale. It provides managed browser instances with built-in CAPTCHA solving, residential proxy rotation, and anti-bot bypass, serving as the infrastructure layer that tools like browser-use, Stagehand, and Skyvern run on top of for reliable web interaction.

Mozilla-backed browser infrastructure for AI agents

Tabstack is Mozilla's browser infrastructure service for AI agents, providing clean markdown extraction, structured JSON data, and automated browser actions through a fast API. With two-tier fetch escalation that achieves sub-600ms latency for static pages, robots.txt compliance, and ephemeral data handling, it offers an ethical alternative to aggressive web scraping tools — complete with an MCP server for Claude and Cursor integration.

Browser automation framework turning websites into action APIs

Notte is a browser automation framework for AI agents that converts any website into a structured action API. Instead of scraping pages for text, Notte lets agents interact with sites — clicking buttons, filling forms, and navigating flows. Built with hybrid AI-plus-deterministic scripting, it includes digital personas, CAPTCHA solving, and proxy management for reliable automation at scale.

Google's Core Web Vitals extension

Google's official Chrome extension for measuring Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift on the current page in real time. Combines local measurements with field data from the Chrome UX Report so developers can see how their lab numbers compare to real user experience. Reached end-of-life in January 2025 as its functionality shipped into the Chrome DevTools Performance panel.

Website technology lookup

Web technology profiler that identifies the frameworks, CMS, analytics, advertising, payment and hosting tools powering any public website. The database tracks 113,000+ internet technologies across 673 million domains, and the browser extension surfaces the full stack of whichever page you are viewing with a single click. Essential for competitive research, sales prospecting, compatibility checks and due diligence.

Developer news aggregator

Curated developer news platform that replaces your browser's new tab with a personalized feed of technical articles, releases and discussions drawn from 1,300+ engineering sources. Smart ranking surfaces content that matches the languages and tools you follow, while Squads let specialized communities discuss frameworks, careers and releases in the open. The fastest way to stay current without building and maintaining a private RSS habit.

Hundreds of GitHub UI enhancements

Open-source browser extension with hundreds of small UX improvements to GitHub: cleaner diffs, one-click PR merging, reaction avatars, linkified commit SHAs, and much more. Fixes dozens of long-standing GitHub UI annoyances that power users encounter daily, making the GitHub web experience feel polished and efficient without waiting for official feature updates.

GitHub code navigation sidebar

Browser extension that adds a file tree sidebar to GitHub repositories for easy code navigation. Browse files and folders without leaving the current page, with support for private repos, pull request code review navigation, file search, bookmarks, and theming. Works with GitHub Enterprise. Available for Chrome, Firefox, Safari, and Edge. Essential for navigating large GitHub repos without cloning. Freemium with Pro features for advanced code review and multiple GitHub accounts.

Pretty-print JSON in the browser

Open-source browser extension that automatically pretty-prints JSON responses in the browser tab. Supports collapsible nodes, syntax highlighting, and raw/formatted toggle. Essential developer tool for anyone who works with APIs regularly, turning unreadable JSON blobs into navigable, color-coded trees that make debugging API responses significantly faster and less error-prone.

Time-travel debugging for Redux

Browser extension for inspecting and debugging Redux state management in React applications. Features time-travel debugging to replay actions step-by-step, state diff viewer showing exactly what changed, action log with payload inspection, state import/export, and ability to dispatch actions manually. Supports Redux Toolkit and legacy Redux. Available for Chrome, Firefox, and as a standalone Electron app. Essential for debugging complex Redux state flows in production and development.

Console for mobile browsers

Open-source mobile web console that embeds a full developer toolkit into any mobile browser. Provides console, element inspection, network monitor, resource viewer, performance timing, and JavaScript execution on devices that lack native DevTools. The de facto standard for debugging responsive layouts, mobile-specific JavaScript errors, and production issues on phones — loaded with a single script tag or a browser extension.

Web page quality auditing

Google's open-source automated tool for auditing web page performance, accessibility, SEO, best practices, and Progressive Web App compliance. Generates detailed reports with actionable improvement suggestions and scores from 0-100 for each category. Built into Chrome DevTools, available as a CLI tool, Node.js module, and via PageSpeed Insights web interface. Essential for web performance optimization and meeting Core Web Vitals thresholds that affect Google search rankings.

Identify web technologies

Wappalyzer is a technology detection service that identifies the tech stack behind any website — frameworks, CMS, analytics, CDNs, payment processors, and 2,500+ other technologies. Available as a browser extension (Chrome, Firefox, Edge), API, CLI, and bulk lookup service. Useful for competitive analysis, sales prospecting, and lead enrichment. Founded 2009 by Elbert Alias, remains independent and bootstrapped — free extension plus paid API and enterprise tiers.

The browser for ambitious developers

Standalone browser built specifically for web developers and designers that shows multiple synchronized viewports side by side for responsive design testing. Features accessibility inspector (WCAG compliance checking), visual regression testing via screenshots, layout debugging overlays, meta tag validator, social media preview cards, and color contrast checker. Reduces the need for constant resizing and device switching during front-end development. Available on macOS, Windows, and Linux.

Responsive web development tool

Open-source browser for responsive web development that shows multiple device viewports simultaneously with synchronized scrolling, clicking, and navigation. Preview your site on phone, tablet, and desktop sizes side by side in real-time. Features screenshot capture for all viewports, element inspector, network monitoring, and hot-reload support. Built on Chromium. Free alternative to Polypane for developers who need quick responsive testing without paid subscriptions. 23K+ GitHub stars.

Debug Vue.js applications

Official browser DevTools extension for Vue.js providing deep inspection of component trees, reactive state, props, events, and slots. Includes Pinia/Vuex store debugging with time-travel, Vue Router inspection, performance timeline, and component highlighting. Works with Vue 2 and Vue 3. Available for Chrome and Firefox with standalone Electron app. Essential for debugging reactivity and understanding component hierarchies in Vue applications.