maratool

A collection of free, browser-based developer, design, and productivity tools. All tools run entirely client-side — no uploads, no accounts, no tracking beyond standard AdSense (eventually, because currently there is no AdSense).

Live at maratool.com.

Why this exists

There's a class of task I kept running into. Calculate a percentage I'm too lazy to do in my head. Strip the background off an image or a GIF. Throw together a phone mockup. Stuff you don't want to install an app for, and definitely don't want to make an account for. For years I'd google whichever site did the thing, ignore the ads, copy the result, close the tab. Repeat next week with a different one.

AI can do some of these, but not always well, and sending private data through an LLM just to extract text from a contract PDF is not what most people want. So this is the alternative: a growing pile of small browser-only tools where the math is right, your data stays on your machine, and nothing is uploaded anywhere.

One honest exception. The Instagram video downloader at /instagram-video-downloader is the only tool that talks to a server. Your browser sends the Instagram URL you paste to a small Cloudflare Worker in worker/, which proxies the request to a third-party Instagram API. This is required because Instagram blocks direct fetches from the browser. The privacy policy documents exactly what that one tool does. Every other tool on the site is fully client-side.

It used to be just for me. Now the source is here, and contributions are open. The full story is on the blog: Why I built maratool, and why it's open source now.

Contributing

PRs welcome. Areas that need help in particular:

• Health calculators. Over a hundred clinical scores live under src/pages/ and src/tools/, each implemented from the primary literature. Clinicians spotting a formula error, an outdated guideline, or a missing calculator: please open an issue or PR.
• New tools. If there's something you wish maratool had, see src/data/tools.ts for the registry, copy a small existing tool (e.g. uuid-generator) as a starting point, and open a PR.
• Fixes. Bug reports with a reproduction step go in GitHub Issues.

License

This project is source-available under the O'Saasy License. You can read, fork, modify, and self-host the code freely. You cannot offer it to third parties as a competing hosted, managed, or SaaS product.

Note: O'Saasy is not an OSI-approved open-source license. It is a source-available license modelled on MIT with an added SaaS-competition clause. See LICENSE for the full text.

Stack

• Framework: Astro (static output, zero JS framework)
• Styling: Plain CSS + CSS variables
• Tool logic: Vanilla JS in src/tools/
• Hosting: Cloudflare Pages (static)
• Instagram media worker: Cloudflare Worker in worker/

Local development

npm install
npm run dev      # http://localhost:4321

Build a production bundle:

npm run build
npm run preview

Run unit tests:

npm test

Deployment

Production runs on Cloudflare Pages. Every merge to main triggers an automatic build and deploy — usually live on maratool.com within 1–2 minutes.

Self-hosting

The site is a pure static build — you can deploy dist/ to any static host (Cloudflare Pages, Netlify, Vercel, GitHub Pages, an S3 bucket). Cloudflare Pages is what we use because it is free and global.

Instagram media tool

The /instagram tool depends on a separate Cloudflare Worker in worker/. To self-host that tool you need:

1. A Cloudflare account.

2. A RapidAPI subscription to the instagram120 API for the primary extraction path.

3. The worker deployed via wrangler deploy with RAPIDAPI_KEY set as a Cloudflare Worker secret:

   cd worker
   wrangler secret put RAPIDAPI_KEY
   wrangler deploy

   Without RAPIDAPI_KEY, the worker still works through the free cobalt.tools and kohi fallbacks, but quality and reliability drop.

4. Update ALLOWED_ORIGIN in worker/wrangler.toml to point at your own domain.

Project structure

src/
├── components/   Astro components (Layout, Sidebar, Topbar, AdColumn, ToolShell, …)
├── data/         tools.ts — central registry of every tool's metadata
├── layouts/      Base.astro — HTML shell, meta, schema
├── pages/        Every tool, blog post, and content page (one .astro per route)
└── tools/        Vanilla JS implementations of each tool

worker/           Cloudflare Worker proxying Instagram media APIs
public/           Static assets served as-is (favicon, robots.txt, vendored libs)
scripts/          Build-time generators (llms.txt, palette JSON, OG images, lastmod)

Reporting issues

• Security vulnerabilities: see SECURITY.md.
• Bugs in a specific tool: open a GitHub issue or email maratool@marcell.com.br.
• Clinical/medical formula corrections: email maratool@marcell.com.br — these are treated as priority.