Free Web Developer Tools — Complete Directory

About onHTML Developer Tools

onHTML is a suite of free, privacy-first developer tools that run entirely in your browser. There are no servers processing your data, no accounts to create, and no usage limits. Every tool from JSON Formatter to Password Generator executes client-side using modern JavaScript and Web APIs.

Why Browser-Based Tools?

When you paste sensitive data — API keys, JWTs, passwords, proprietary JSON — into a server-side tool, that data leaves your network. With onHTML, your data stays on your device. The JWT Decoder never sees your tokens. The Hash Generator never sees your input. This matters for security-conscious developers and teams with compliance requirements.

Formatters and Validators

The formatting tools convert minified or unreadable data into structured output. The JSON Formatter applies RFC 8259 formatting rules, catches invalid JSON with exact error positions, and minifies for production. The Regex Tester runs your patterns in real time against test strings, showing match groups and positions. The Markdown Editor renders CommonMark and GFM syntax with live preview.

The Diff Checker uses the Myers diff algorithm — the same algorithm powering git diff — to highlight exact changes between two text blocks. For comparing JSON objects semantically (ignoring key order), the JSON Diff tool understands JSON structure rather than treating it as plain text.

Converters

The converter category handles the everyday transformations that interrupt workflow. The Base64 Encoder handles both standard Base64 and the URL-safe variant (base64url) used in JWTs and OAuth tokens. The JWT Decoder lets you inspect header, payload, and signature claims without any backend — essential when debugging authentication issues.

The JSON ↔ YAML Converter handles the bidirectional conversion needed when moving between application code (JSON APIs) and infrastructure configs (Kubernetes YAML, GitHub Actions). The cURL to Code Converter turns the commands you copy from DevTools or API documentation into fetch, axios, or Python requests snippets instantly.

For frontend developers, the HTML to JSX Converter handles the class→className, for→htmlFor, and self-closing tag transformations automatically. The Tailwind ↔ CSS Converter bridges the gap between utility-first and traditional CSS workflows.

Generators

The generator tools create content you'd otherwise have to write or calculate manually. The Password Generator uses crypto.getRandomValues() — the same entropy source as your OS — to produce passwords with measurable entropy. A 16-character password with mixed character types gives you approximately 105 bits of entropy, effectively immune to brute force with any foreseeable computing power.

The UUID/ULID Generator produces RFC 4122 v4 UUIDs and sortable ULIDs for use as database primary keys. The Mock JSON Generator creates realistic test data with proper types (names, emails, UUIDs, dates) — critical for frontend development that shouldn't depend on a running backend.

For SEO workflows, the Meta Tag Generator produces the full set of Open Graph, Twitter Card, and technical SEO tags. The Schema Generator creates valid JSON-LD structured data for Google's rich results. The Sitemap Generator and robots.txt Generator complete the technical SEO toolkit.

CSS Tools

The CSS tools replace the mental overhead of memorizing syntax. The Gradient Generator covers linear, radial, and conic gradients with color stops, hard stop patterns, and repeating variants — with the CSS output ready to copy. The Box Shadow Generator handles multiple shadows, inset shadows, and neumorphism presets.

The Glassmorphism Generator produces the backdrop-filter CSS with browser prefixes, while the CSS Loader Generator creates pure-CSS spinners and skeleton screens that run on the GPU compositor without triggering layout or paint.

The Cubic-Bezier Visualizer gives you a drag-and-drop editor for custom easing functions with a live preview of the animation. The Border Radius Generator handles the full 8-value syntax for creating organic blob shapes.

Frequently Asked Questions

Are these tools really free?

Yes. Every tool on onHTML is free to use without registration, subscription, or usage limits. The site is sustained by privacy-respecting advertising.

Is my data safe?

All tools process data in your browser using JavaScript. Your data is never transmitted to onHTML servers. You can verify this by opening DevTools → Network tab — you'll see zero API calls when using any tool.

Do the tools work offline?

After the initial page load, most tools work without internet access since they run entirely in JavaScript. Tools that fetch external data (like the HTTP Headers Inspector) require an active connection.

Can I use these tools in my team?

Yes. Share any tool URL directly with teammates. No accounts or permissions needed.

How many tools are available?

Currently 56 tools across 4 categories, with new tools added regularly. Subscribe to the RSS feed for announcements, or check the developer blog for guides.