Development Tools Web Apps

Google's image compression tool — compare formats (WebP, AVIF, MozJPEG) side by side with live quality sliders. All processing is client-side, so images never leave your machine. A must-have for web developers.

Social front-end playground: write HTML, CSS and JavaScript in the browser with live preview, preprocessors and frameworks, then share pens and explore millions of community demos. Free accounts cover public work.

Cloud development environment for full projects: instant Node, React and framework templates, npm dependencies, live collaboration and shareable dev servers. Free tier covers public sandboxes and limited VM credits.

Instant dev environments that boot Node.js inside your browser tab via WebContainers — full npm installs and Vite dev servers with no remote VM. Free for public projects.

Browser IDE and hosting for dozens of languages with an AI agent that scaffolds and edits apps, real-time multiplayer editing, and one-click deployments. Free tier for trying and learning.

Regex sandbox with live matching, a full explanation tree for every token, a debugger that steps through backtracking, and quick reference for PCRE, JavaScript, Python and Go flavors.

Visualizes JSON, YAML, CSV and XML as an interactive node graph so nested structures become readable at a glance. Open-source; free tier handles typical payloads in the browser.

Browser compatibility tables for web platform features — search any CSS property, JavaScript API or HTML element and see support across browsers and versions with usage-share statistics.

Turns source code into beautiful, syntax-highlighted images for tweets, slides and documentation, with configurable themes, fonts, window chrome and export sizes. Free and no account needed.

Minimal code-to-image tool by the Raycast team: paste code, pick a gradient theme and export a crisp PNG or SVG for slides and social posts. Free, no signup.

Instant plain-English translation of cron schedule expressions as you type, with examples and edge-case notes. The de facto reference for double-checking a crontab before deploying it.

Unified, searchable API documentation for hundreds of languages and frameworks in one fast interface, with offline support and fuzzy search. Free and open source, maintained by freeCodeCamp.

Run SQL directly in the browser against SQLite, plus server-side MariaDB, PostgreSQL and MS SQL sandboxes — import CSV, run queries, export results, no installation or signup.

Draw entity-relationship diagrams by writing a simple DSL — tables and refs become a tidy visual schema you can export to SQL, PNG or PDF. Free tier covers up to ten diagrams.

The reference OpenAPI editor: write API specs in YAML with real-time validation, documentation preview and code generation for servers and clients. Free and open source.

Open-source API client in the browser: REST, GraphQL, WebSocket, SSE and MQTT requests with collections, environments and team workspaces. A lightweight alternative to Postman with a free tier.

Decode, inspect and verify JSON Web Tokens in the browser: paste a token to see header and payload claims instantly, check signatures, and browse libraries for every language.

GCHQ's open-source 'cyber Swiss army knife': chain hundreds of operations — base64, hex, compression, hashing, encryption, parsing — into recipes that transform data entirely client-side.

Community platform for writing and sharing WebGL fragment shaders: live-code GLSL in the browser and explore thousands of procedural graphics, raymarching scenes and audio-reactive experiments.

Google's page performance analyzer: enter a URL to get lab Lighthouse scores plus real-user Core Web Vitals field data, with prioritized suggestions for improving load and interactivity.

Reactive JavaScript notebooks for data exploration and visualization — cells re-run automatically as values change, with D3 and Plot built in. Free tier for public notebooks.

Visual Studio Code running entirely in the browser at vscode.dev: open local folders via the File System Access API or GitHub repos, with extensions, themes and settings sync. Free.

Official playground for Mermaid: write flowcharts, sequence diagrams, Gantt charts and ER diagrams as text and see them render live, with SVG/PNG export and shareable links. Open source.

Instantly get a unique URL that captures and displays every HTTP request sent to it — headers, body, query strings — for debugging webhooks and callbacks. Free without signup.

Smart lossy compression for PNG, JPEG, WebP and AVIF images — typically 50-80% smaller with no visible quality loss. Free for batches up to 20 images at 5 MB each.

Compare two texts, images, PDFs or spreadsheets side by side with highlighted differences. The text diff is free without an account; handy for contracts, code and document revisions.

The world's largest code hosting platform: Git repositories, pull requests, issues, Actions CI/CD, Codespaces and project boards. Free plan includes unlimited public and private repositories.

The hub of open machine learning: hundreds of thousands of models, datasets and browser-runnable Spaces demos, with free hosting for public repositories and community discussion.

Open-source backend platform: hosted Postgres with instant APIs, authentication, storage, realtime subscriptions and edge functions. Free tier includes two projects for hobby apps, making it a popular open alternative to Firebase for shipping side projects quickly.

Frontend cloud for deploying web apps from a Git push — preview deployments per pull request, edge network, serverless functions and first-party Next.js support. Generous free hobby tier.

Platform for deploying static sites and web apps from Git with build pipelines, serverless functions, forms and edge redirects. Free tier suits personal projects and prototypes.