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



reCAPTCHA is described as 'Free service that protects your site from spam and abuse, using risk analysis techniques to tell humans and bots apart' and is a very popular Anti-Spam tool in the security & privacy category. There are more than 25 alternatives to reCAPTCHA, not only websites but also apps for a variety of platforms, including SaaS, Self-Hosted, PHP and JavaScript apps. The best reCAPTCHA alternative is Cap Captcha, which is both free and Open Source. Other great sites and apps similar 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.




GeeTest protects your websites, mobile apps and APIs from bad bot attacks with zero user friction. Its self-learning defense model based on Graph Convolutional Networks and massive volumes of biometric data collected in the past 7 years allows GeeTest to identify and mitigate...




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.




The Arkose Labs platform undermines the economic drivers behind fraud until perpetrators are compelled to abandon attacks. Real-time risk classification of traffic with interactive enforcement challenges, the solution defeats automated attacks...

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