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



NoBot CAPTCHA API is described as 'Developer-friendly alternative to Google reCAPTCHA that helps prevent automated bot traffic without compromising user privacy' and is a Anti-Spam tool in the security & privacy category. There are more than 25 alternatives to NoBot CAPTCHA API for a variety of platforms, including Web-based, SaaS, Self-Hosted, PHP and JavaScript apps. The best NoBot CAPTCHA API alternative is Cap Captcha, which is both free and Open Source. Other great apps like NoBot CAPTCHA API are Anubis, reCAPTCHA, Procaptcha and Private Captcha.
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.

reCAPTCHA is a free service that protects your site from spam and abuse, using risk analysis techniques to tell humans and bots apart.


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.




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.




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.





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.
hCaptcha is designed to solve the most labor intensive problem in machine learning: labeling massive amounts of data in a timely, affordable, and reliable way.



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.




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...
