# <img src="https://github.com/tiagozip/cap/blob/main/docs/public/logo-small.webp?raw=true" alt="" align="left" width="40" height="40"> Cap

Cap is a lightweight, modern open-source CAPTCHA alternative using <a href="https://capjs.js.org/guide/effectiveness.html">SHA-256 proof-of-work</a>. It's fast, private, and extremely simple to integrate.

<a href="https://capjs.js.org/guide/demo.html"><img src="./assets/captcha.svg" alt="Cap widget" width="250"></a>

## Documentation

**[Read the docs](https://capjs.js.org)**, try the [demo](https://capjs.js.org/guide/demo.html) or read the [feature comparison](https://capjs.js.org/guide/alternatives.html)

## What is Cap?

Cap replaces visual captchas with modern, accessible and privacy-preserving <a href="https://capjs.js.org/guide/effectiveness.html">proof-of-work challenges</a>. No images, no tracking, no dependencies, works everywhere.

You can either run it on any JavaScript runtime, or use the standalone mode with Docker. [Learn more about how Cap works](https://capjs.js.org/guide/)

## Why Cap?

- **250x smaller than hCaptcha**  
  ~20kb, zero dependencies, loads in milliseconds

- **Privacy-first**  
   Cap doesn't send any telemetry back to our servers

- **Fully customizable**  
   Change the colors, size, position, icons and more with CSS variables

- **Proof-of-work**  
   Your users no longer have to waste time solving visual puzzles.

- **Standalone mode**  
   Run Cap anywhere with a Docker container with analytics & more

- **Invisible**  
   Hide Cap's widget and solve challenges in the background

- **M2M**  
   Keep your APIs protected while accessible to friendly robots

- **Open-source**  
   Completely free & open-source under the Apache 2.0 license

Cap is a great alternative to [reCAPTCHA](https://www.google.com/recaptcha/about/), [hCaptcha](https://www.hcaptcha.com/) and [Cloudflare Turnstile](https://developers.cloudflare.com/turnstile/)

## License

This project is licensed under the Apache-2.0 License, please see the [LICENSE](https://github.com/tiagozip/cap/blob/main/LICENSE) file for details.

Copyright ©2025 - present [tiago](https://tiago.zip)

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Cap's free instance is supported by DigitalOcean for open-source. <a href="https://www.digitalocean.com/?refcode=7e41cf645be3&utm_campaign=Referral_Invite&utm_medium=Referral_Program&utm_source=badge">Try DigitalOcean</a> and get $250 worth of credits.

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