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Open Source CAPTCHA & Bot Protection Tools

A curated collection of the best open source tools for distinguishing humans from bots (CAPTCHA) and preventing spam..

Cap

Privacy-first CAPTCHA alternative with proof-of-work

  • Stars

    Stars growing over the last 30 days8,390

  • Last commit

    10 hours ago

  • License

    Apache-2.0
Lightweight open-source CAPTCHA solution using SHA-256 proof-of-work. 250x smaller than hCaptcha, fully customizable, and privacy-focused with zero telemetry.

Open Source Alternative to:

reCAPTCHA

ALTCHA

Next-Gen CAPTCHA and Spam Protection, GDPR compliant

  • Stars

    2,901

  • Last commit

    2 days ago

  • License

    MIT
ALTCHA offers cutting-edge spam and abuse protection for websites and apps, with privacy-friendly CAPTCHA alternatives designed for GDPR compliance.

Open Source Alternative to:

Cloudflare Turnstile

mCaptcha

Privacy-first proof-of-work CAPTCHA without user friction

  • Stars

    2,502

  • Last commit

    1 year ago

  • License

    AGPL-3.0
Privacy-focused proof-of-work CAPTCHA system that silently protects websites without tracking users or requiring image solving. Drop-in replacement for reCAPTCHA.

Open Source Alternative to:

reCAPTCHA

Procaptcha

Decentralized CAPTCHA for enhanced web security

  • Stars

    303

  • Last commit

    8 hours ago

  • License

    Apache-2.0
A blockchain-based CAPTCHA solution offering improved security, user experience, and resistance to bot attacks for web applications.

Open Source Alternative to:

reCAPTCHA

Private Captcha

GDPR-compliant bot protection without user friction

  • Stars

    199

  • Last commit

    5 hours ago

  • License

    Unknown
Privacy-first CAPTCHA service that blocks bots while keeping forms accessible. No puzzles, no tracking, no cookies - just invisible cryptographic protection.

Open Source Alternative to:

reCAPTCHA

Friendly Captcha

Invisible bot protection that respects user privacy

  • Stars

    37

  • Last commit

    2 days ago

  • License

    MPL-2.0
Privacy-compliant CAPTCHA alternative using proof-of-work technology. Protects websites from bots and spam without user interaction or data tracking.

Open Source Alternative to:

reCAPTCHA

OneHuman

Access control for AI agents your customers log in with

  • Stars

    23

  • Last commit

    10 days ago

  • License

    BUSL-1.1
Detects AI agents using customer credentials, masks private fields, holds risky actions for passkey approval, and signs every decision on your own server.

Open Source Alternative to:

HUMAN Security
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