Cap Captcha icon
Cap Captcha icon

Cap Captcha

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

Cap Captcha screenshot 1

Cost / License

  • Free
  • Open Source

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Platforms

  • Self-Hosted
  • Docker
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Security & Privacy, Development

GitHub repository

  •  7,965 Stars
  •  611 Forks
  •  9 Open Issues
  •   Updated  
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Our users have written 2 comments and reviews about Cap Captcha, and it has gotten 30 likes

Cap Captcha was added to AlternativeTo by Paul on and this page was last updated .

Comments and Reviews

   
Top Negative Comment
forgetso
2

PoW does not stop bots, it only slows them down.

Darlene Sonalder
0
App tester and reviewer at Great App Testing Ltd.

PoW is great to fight spam, however I wonder how this perform on mobile. Today mobile browsing is huge and the UX of PoW would kill the batteries fast no ?

forgetso
Replying to @Darlene Sonalder

Only if the PoW was difficult. Most PoWs in CAPTCHA products are completed in seconds and do not deter bots. You need dynamically adapting PoW products like Procaptcha to stand a chance of stopping bots, as opposed to just slowing them down.

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Selfhosting

Selfhosting is where you're hosting your own websites, apps, software, tools, and much more on your own server instead of having to rely on 3rd-party cloud providers such as Hetzner. Taking this approach to hosting gives you more control over your data and how your server or servers are managed. When you are running multiple things on one or two servers, within your home, it's called a "Homelab" and you're "Homelabbing" at that point. Running your own server and homelab within your home is great for privacy-conscious individuals such as myself, tech enthusiasts, small businesses, and those seeking more control of their digital life. The following lists provided here are applications and software I've gotten comfortable with and enjoyed using over the past 3 and a half years since I started homelabbing, it's based on my experience and what fits my criteria. Some well known softwares won't be listed here, as my experience may of not been at best with them. My criteria is that software is built in the open, respects user privacy and security, should not require a license to operate, and don't contain profanity and other minor things. I'm also willing to test new software to selfhost, feel free to comment or message me to try out other alternatives. There are other places to check out as well for those interesting selfhosting, such as Awesome Selfhosted, selfh.st, and other places you can find on the internet. https://github.com/awesome-selfhosted/awesome-selfhosted https://github.com/awesome-foss/awesome-sysadmin https://github.com/veggiemonk/awesome-docker If you ever need help with selfhosting, you can check out the following communities: Homelab Community on Fluxer, I personally run /r/selfhosted (Reddit) /c/selfhosted (Lemmy / Fediverse) There's also a wiki you can look into as well. If you believe an alternative software should be added to this list, please contact me or direct message via my AlternativeTo account. I'm also available on Signal. This lists gets updated every month at least, check back regularly.
By Korbs81 appsUpdated

Official Links

What is Cap Captcha?

Cap is a lightweight, modern open-source CAPTCHA alternative designed using SHA-256 PoW.

It's:

  • 250x smaller than hCaptcha @cap.js/widget is extremely small, only 12kb minified and brotli'd.

  • Private Cap's usage of proof-of-work eliminates the need for any tracking, fingerprinting or data collection.

  • Fully customizable Cap's self-hostable so you can customize both the backend & frontend — or you can just use CSS variables

  • Proof-of-work Cap uses proof-of-work instead of complex puzzles, making it easier for humans and harder for bots

  • Standalone mode Cap offers a standalone mode with Docker, allowing you to use it with languages other than JS.

  • Invisible mode Cap can run invisibly in the background using a simple JS API.

  • Floating mode Cap's floating mode keeps your CAPTCHA hidden until it's needed.

  • Fully open-source Completely open source under the Apache license 2.0 license.

Ideal for protecting APIs from bots, preventing spam on forms, blocking automated login attempts, and securing free-tier abuse. It's a modern alternative for reCAPTCHA, hCaptcha and Cloudflare Turnstile, but unlike them, Cap is computation-bound, not tracking-bound. Cap is built with JavaScript, runs on any JS runtime (Bun, Node.js, Deno), and has no dependencies. If you're not using any JS runtime, you can also use the standalone mode with Docker, which relies entirely on a simple REST API to create and validate challenges.