# cap — modern, lightning-quick PoW captcha
Cap is a lightweight, modern open-source CAPTCHA alternative designed using SHA-256 PoW.
| [Learn more](https://capjs.js.org)
|----------|
[](https://www.npmjs.com/package/@cap.js/server) [](https://www.npmjs.com/package/@cap.js/widget) [](https://www.bestpractices.dev/projects/9920)
## Why Cap?
- ⚡️ **250x smaller than hCaptcha**
Cap's widget library is extremely small, only 12kb minified and brotli'd.
- 🔒️ **Private**
Cap's usage of proof-of-work eliminates the need for any tracking, fingerprinting or data collection.
- 🌈 **Fully customizable**
Cap is self-hostable so you can customize both the backend & frontend — or you can just use CSS variables
- 🤖 **PoW-based**
Cap uses proof-of-work instead of complex puzzles, making it easier for humans and harder for bots
- 🧩 **Standalone mode**
Cap offers a standalone mode with Docker, allowing you to use it with languages other than JS.
- 💨 **Invisible mode**
Cap can run invisibly in the background using a simple JS API.
- ☁️ **Floating mode**
Floating mode keeps your CAPTCHA hidden until it's needed
- 🌳 **Fully FOSS**
Completely open source under AGPL-3.0, with no premium versions.
## Star History
[](https://www.star-history.com/#tiagorangel1/cap&Date)