100 free developer tools that run in your browser (and how I built 1,066 of them)

FreeToolr is a free website with 1,066 online tools. About 100 of them are developer tools, and almost all of them run entirely in your browser. I'm AK Shine, and I designed and built it. This post is the developer's tour: what's there, how it's built, and what you can embed on your own site.

The developer tools

The Developer Tools hub covers the small jobs that interrupt a day of real work:

• JSON: JSON formatter, validator, diff checker, JSONPath tester, and converters from JSON to TypeScript, Zod, Go structs, Python, Java and C# classes.
• Encoding: Base64, URL, HTML entities, JWT decode and encode, Punycode, ROT13, gzip compress and decompress.
• Testing: regex tester, cron expression parser and generator, CORS and API testers.
• Front end: CSS clamp, grid, gradient, box-shadow and cubic-bezier generators, px to rem, CSS to Tailwind, HTML to JSX, SVG to JSX.
• Config: .gitignore, Docker Compose, nginx config, htpasswd, license and README generators.
• Playgrounds: JavaScript, Python and SQL playgrounds that run client side.

No account, no rate limit, no paste-your-secret-into-our-server. The JWT decoder decodes in the page; the token never leaves your machine.

How it's built

A few decisions made 1,066 tools possible for a very small team:

1. One registry drives everything. Each tool is one record in a registry package: name, category, inputs, explanation, FAQs, related tools. Tool pages, category hubs, the search index, sitemaps, JSON-LD and llms.txt are all generated from it. Adding a tool is adding a record and an engine.
2. Static first. The site is Astro with output: 'static' and React islands only where a page needs interaction, deployed to Cloudflare Pages. No server rendering at all.
3. Tools run in the browser. PDF, image, video and audio tools process files with JavaScript and WebAssembly on the device. Server code exists only where a browser can't do the job: fetching another site for an SEO check, or calling an AI model with a secret key. Those run on Cloudflare Workers.
4. Test vectors per tool. Tool engines ship with input and output vectors; the current suite runs a little over 3,300 checks before a deploy.
5. Zero running cost apart from AI. Static hosting, free tiers and client-side processing keep the bill at zero, which is what lets the tools stay free with no premium tier.

Embed a calculator on your site

31 calculators can be embedded with one iframe snippet. Each embeddable tool page has an "Add this to your website" box with the code to copy. It's free, there's no key, and the widget is the same tool that runs on FreeToolr.

Beyond the developer tools

There are 16 categories in total: PDF, images, calculators, finance (with local pay and tax rules for the US, the UK and Europe, Nigeria and the Gulf), health, converters, date and time, students, text, SEO, AI writing helpers, video and audio, social media, business and security. There's also a free Workspace with reminders, tasks, a focus timer and notes.

The full tour of every section is in the original guide: What is FreeToolr? A guide to 1,000+ free online tools.

If there's a developer tool you reach for that's missing, tell me in the comments. That's how the list grows.