Best / CAPTCHA and bot protection
Best open-source CAPTCHA and bot protection
The best self-hosted CAPTCHA split in the c17.io catalog is ALTCHA for an MIT proof-of-work widget (the published Google reCAPTCHA / hCaptcha path), mCaptcha when you want that AGPL-3.0 PoW backend — /compare/altcha-vs-mcaptcha, SuperTokens or PocketBase when the job is login rather than a bot widget — /best/auth-identity, and Formbricks when the job is the form the widget sits on — /best/forms-surveys. This is not reCAPTCHA Enterprise scores, hCaptcha's every accessibility pack, or Cloudflare Turnstile (not open source — this site skips it). App login stays on /replace/clerk.
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Ranked picks
1
ALTCHAMIT proof-of-work widget (2,831 stars in the catalog) — the c17 reCAPTCHA / hCaptcha path. /compare/altcha-vs-mcaptcha.
When to pick it: A challenge on a form you already host.
2,831 stars in the catalog
2
mCaptchaAGPL-3.0 PoW backend (2,493 stars in the catalog). /compare/altcha-vs-mcaptcha.
When to pick it: A self-hosted backend if ALTCHA is not the shape.
2,493 stars in the catalog
3
KeycloakApache-2.0 IdP already on /best/auth-identity. Not a bot widget.
When to pick it: Workforce SSO if the job was the login, not the CAPTCHA.
37,403 stars in the catalog
4
FormbricksSurveys already on /best/forms-surveys. Not a CAPTCHA.
When to pick it: The form the widget protects.
13,113 stars in the catalog
How they compare
| Tool | License | Self-host | Best for |
|---|---|---|---|
| ALTCHA | MIT License | Easy | A challenge on a form you already host. |
| mCaptcha | AGPL-3.0 | Medium | A self-hosted backend if ALTCHA is not the shape. |
| Keycloak | Apache License 2.0 | Medium | Workforce SSO if the job was the login, not the CAPTCHA. |
| Formbricks | GNU Affero General Public License v3.0 | Easy | The form the widget protects. |
Related pages
- ALTCHA / mCaptcha stack
- Auth without the bill stack
- Formbricks stack
- Replace Google reCAPTCHA
- Replace hCaptcha
- Replace Clerk
- Replace Auth0
- Replace WorkOS
- Replace Amazon Cognito
- Replace Firebase Auth
- Replace Stytch
- Replace Typeform
- Replace Google Forms
- Replace SurveyMonkey
- Replace Jotform
- Replace Tally
- Replace Sprig
- Replace Maze
- Replace UserTesting
- Replace Paperform
- Replace Formstack
- ALTCHA vs mCaptcha
- All best open-source pages
- All compare pages
- All replace pages
- All stacks
- Tools catalog
FAQ
- ALTCHA or mCaptcha?
- ALTCHA if you want the published MIT widget. mCaptcha if you want that AGPL backend — /compare/altcha-vs-mcaptcha.
- hCaptcha or reCAPTCHA?
- Same published widget — /replace/hcaptcha and /replace/google-recaptcha.
- Why not Turnstile?
- Cloudflare Turnstile is not open source. This site skips it.
- Are these free?
- ALTCHA is MIT. mCaptcha is AGPL-3.0. Keycloak is Apache-2.0. Formbricks is AGPL as listed on its stack. You pay hosting. Template users never pay c17.
- How do I deploy it?
- Open /stacks/altcha-captcha. Drop the vendor script. Confirm one form submit.
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