Lightweight, modern open-source CAPTCHA alternative designed using SHA-256 proof-of-work and JS instrumentation



The best free alternative to reCAPTCHA is Cap Captcha, which is also Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to reCAPTCHA and many of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to reCAPTCHA are Anubis, hCaptcha, Procaptcha and Cloudflare Turnstile.
Lightweight, modern open-source CAPTCHA alternative designed using SHA-256 proof-of-work and JS instrumentation



Applies sha256 proof-of-work challenges to incoming HTTP requests, targeting AI crawlers, bots that ignore robots.txt, and automated scrapers, protecting server resources and preventing unwanted search engine indexing for privacy-focused sites.

Prosopo Procaptcha redefines user verification with a unique approach that emphasizes privacy and security. It's a pioneering solution designed to offer an alternative to conventional CAPTCHA systems that often compromise user privacy.




Turnstile is Cloudflare's smart CAPTCHA alternative. It automatically chooses from a rotating suite of non-intrusive browser challenges based on telemetry and client behavior exhibited during a session.
ALTCHA is a privacy-first solution built to help developers and website owners stop bots, spam, and automated abuse — without making things harder for real users. It replaces traditional CAPTCHA systems with a smarter, quieter approach to verification and threat detection.

Friendly Captcha is a leading cybersecurity company with a clear mission: to reliably defend against modern bot attacks and spam while complying with the GDPR and other privacy regulations. As Germany's largest CAPTCHA provider, Friendly Captcha uses innovative technology to...

mosparo is the modern solution for protecting your online forms from spam. The protection method is quite simple: mosparo blocks spam using rules matching the form’s data. The detection method is comparable to an e-mail spam filter.




Private Captcha is an independent, privacy-first, self-hostable Proof-of-Work CAPTCHA service made in EU. Instead of asking users to solve complex puzzles or track their behavior, Private Captcha solves an invisible cryptographic task in the background.




MTCaptcha is a smart captcha service that prioritizes privacy and accessibility. It offers an adaptive invisible noCaptcha that is easy for humans but hard for bots, making verification frictionless. MTCaptcha is GDPR and WCAG compliant, ensuring that your data is never sold or...




TrustCaptcha is a privacy-first, invisible CAPTCHA that protects your website from bots and spam—without disrupting your users.




I tried cap captcha on my site and the bots just kept on spamming me.