🆚 Altcha vs. Cap

Altcha is an open-source, privacy-first, self-hosted captcha alternative that uses a proof-of-work mechanism to protect websites, APIs, and online services from spam and unwanted content.

It performs client-side computational challenges based on hashing and memory-hard algorithms such as Argon2 and Scrypt, adds headers and signatures for verification, operates without cookies, fingerprinting, or external requests, and supports more than 50 languages to meet accessibility and privacy requirements.

Cap is an open-source, self-hosted reCAPTCHA alternative that verifies visitors without visual puzzles, tracking, or third-party services.

It uses a two-layer verification model that combines proof-of-work challenges accelerated with WebAssembly and Web Workers, including SHA-256 hashing and optional GPU-resistant time-locks.

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Popularity

Determined by the number of sites using each technology.

• ⭐ 4th most popular in France in the Captchas category.
• ⭐ 5th most popular in Germany in the Captchas category.
• ⭐ 5th most popular in the United States in the Captchas category.
• ⭐ 7th most popular in France in the Spam Protection category.
• ⭐ 7th most popular in the United States in the Spam Protection category.

Top sites

Top-ranked sites that use these technologies.

Compare alternatives

Technologies with similar characteristics.

• Altcha vs. reCAPTCHA
• Altcha vs. hCaptcha
• Altcha vs. Cloudflare Turnstile
• Altcha vs. Yandex SmartCaptcha
• Altcha vs. Friendly Captcha

• Cap vs. reCAPTCHA
• Cap vs. hCaptcha
• Cap vs. Cloudflare Turnstile
• Cap vs. Yandex SmartCaptcha
• Cap vs. Friendly Captcha

• Altcha technology profile

• Cap technology profile