Cap
Cap provides a self-hosted, open source alternative to CAPTCHA challenges for websites.
About Cap
Cap is a self-hosted alternative to hosted CAPTCHA services for websites. It uses two checks together: proof-of-work with SHA-256 and time-lock challenges, and server-generated JavaScript that verifies the browser environment through DOM operations, with no visual puzzles.
It runs on the operator's own server and is licensed under Apache 2.0. The project states it uses no third-party network requests and sets no cookies. The widget is about 20 kB with no dependencies and can be styled with CSS variables. Use requires hosting a server instance, and migration from reCAPTCHA or hCaptcha requires replacing client-side code with Cap's widget.
Key features
- Self-hosted CAPTCHA that runs on operator's own server
- Proof-of-work with SHA-256 and time-lock challenges in WASM
- Server-generated JavaScript instrumentation checks browser environment
- Invisible operation with no visual puzzles
- Customizable colors, size, position via CSS variables
- siteverify API compatible with reCAPTCHA and hCaptcha
Best for: Website operators who want to run CAPTCHA protection on their own servers without third-party requests.
Good for
- Runs on the operator's own server without third-party network requests
- Verification without visual puzzles
- Apache 2.0 licensed code that can be audited and self-hosted
Watch out for
- Requires hosting and maintaining a server instance
- Migration requires replacing client-side code with Cap's widget
Cap at a glance
- Website
- trycap.dev
- Category
- Privacy & Security › Security Tools
- Type
- Website
- Pricing
- Not confirmed. Check the site
- Platforms
- Web
- Open source
- Not stated
- Language
- English
- Last checked
- Oct 5, 2026 · Online when checked
- Listed
- Oct 5, 2026
Guides for Security Tools
Cap alternatives
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Cap FAQ
Can I migrate from reCAPTCHA or hCaptcha?
Yes. Cap's siteverify API is compatible, but client-side code must be changed to use Cap's widget.
How does Cap verify users without visual puzzles?
Each challenge performs proof-of-work and runs server-generated JavaScript instrumentation checks at the same time.
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