Cap is a lightweight, modern open-source CAPTCHA alternative using SHA-256 proof-of-work. It's fast, private, and extremely simple to integrate.

Read the docs, try the demo or read the feature comparison

Cap replaces visual captchas with modern, accessible and privacy-preserving proof-of-work challenges. 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

• 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, hCaptcha and Cloudflare Turnstile

This project is licensed under the Apache-2.0 License, please see the LICENSE file for details.

Copyright ©2025 - present tiago