A few weeks ago I shared CollateKit, my collection of free browser tools. I've since added a new one that's quite different from the text tools: an online protractor.
What it does
- Drag to measure: grab the arm and move it. It works with mouse and touch.
- Type an exact angle: enter a number and the protractor jumps to it.
- 180° and 360° modes: switch between a half-circle and a full-circle protractor.
- Angle details: it shows the complement, the supplement, and whether the angle is acute, right, obtuse, straight or reflex.
- Image mode: upload a photo or screenshot, click three points (arm, vertex, arm), and get the angle between them.
- Copy result: one click to copy the number.
Everything runs in your browser. Nothing is uploaded, and there's no sign-up.
Why I made it
Most tools on the site work with text. I wanted something that does a job an AI chatbot can't do for you: measuring an angle on your own screen or in your own picture. Students, designers and DIY people search for this all the time, and the existing tools I found were cluttered with ads or clumsy on a phone.
How it's built
It's plain JavaScript, with no libraries. The site itself uses Astro and Tailwind and is hosted on Cloudflare Pages. The angle comes from Math.atan2, and pointer events handle mouse and touch with the same code. In image mode, clicks are converted from screen pixels to image pixels, so the angle stays correct even when the photo is scaled down.
What I'd like to add next
I'm thinking about a camera overlay, so you can hold the protractor over a real object, and a tilt mode for phones. I'd also like to add more tools that need your device or your files rather than just text.
Feedback welcome
If you try it, tell me what feels wrong, especially on your phone. And if there's a small browser tool you wish existed, drop it in the comments and I may build it.
You can also see the rest of the tools in my earlier post or on CollateKit.
