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250x smaller than hCaptcha
~20kb, zero dependencies, loads in milliseconds
CapThe modern, open-source CAPTCHA
Lightweight, self-hosted, privacy-friendly, and designed to put you first. Switch from reCAPTCHA in minutes.
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What is Cap?
Cap is the modern, open-source alternative to traditional CAPTCHAs that uses proof-of-work instead of annoying visual puzzles.
It's built with JavaScript and Rust and has no dependencies. You can either run it on any JavaScript runtime (Bun, Node.js, Deno), or use the standalone mode with Docker.
Cap is built into 2 main parts. The widget is a small client-side JavaScript library using custom components and WASM that renders the CAPTCHA and solves the challenge.
The Standalone Server is a Docker image that helps you use Cap with any language or framework. As an alternative, if your server-side uses JavaScript, you can use the lighter server library.
Cap also has a M2M library that implements a custom proof-of-work solver for protecting API endpoints that you still want public.
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
It's ideal for protecting APIs from bots, preventing spam on forms, blocking automated signup attempts and securing free-tier abuse.
Cap is a great alternative to reCAPTCHA, hCaptcha and Cloudflare Turnstile. Check out the feature comparison to see how Cap compares to other CAPTCHAs.
License
Apache 2.0
Copyright (c) 2025–present tiago
