Cap is a modern, open-source CAPTCHA alternative that leverages SHA-256 proof-of-work (PoW) to verify users without relying on tracking, cookies, or intrusive puzzles. Designed to be lightweight and privacy-focused, Cap offers a seamless user experience by eliminating the need for traditional CAPTCHA challenges. Its widget library is exceptionally small—approximately 12KB when minified and compressed—making it about 250 times smaller than hCaptcha.
Cap is fully customizable and self-hostable, allowing developers to tailor both backend and frontend components to their specific needs. It supports various integration modes, including invisible and floating widgets, and provides middleware for frameworks like Express and Hono. For non-JavaScript environments, Cap offers a standalone Docker-based server, enabling use with any language via a simple REST API. Licensed under Apache 2.0, Cap is an ideal solution for protecting APIs, forms, and login systems from bots and spam while ensuring user privacy.