ALTCHA

ALTCHA is an open-source captcha and bot-protection toolkit developed by ALTCHA s.r.o. in Brno, Czech Republic, with the trademark registered in the EU. The core widget is MIT-licensed and uses a proof-of-work challenge solved silently by the browser, with no visual puzzles and no cookies; the bundle is around 34 kB minified and supports 50+ languages including RTL. ALTCHA can be used fully self-hosted with no external calls or data sharing, and a commercial Sentinel platform adds threat intelligence, machine-learning detection and rate-limiting on Docker, Kubernetes, AWS ECS and Azure (30-day trial). The project is GDPR / WCAG 2.2 AA / EAA compliant and source code lives at github.com/altcha-org/altcha.