Cap is a lightweight, modern open-source CAPTCHA alternative designed using SHA-256 proof-of-work and JS instrumentation. It's: - β‘οΈ 250x smaller than hCaptcha - ποΈ Private - π Fully customizable - π€ PoW-based - π³ Fully FOSS - π¨ Invisible
I'm a bit concerned about it's effectiveness. Prove me wrong, I'd be happy if this works as good as the others.
First, this does not verify if I'm a human, but if I have enough computational resources. A similar system was developed (Hashcash) which is not really used in popular email clients. In my opinion, it works for Bitcoin for the same reason it didn't work work email: it doesn't verify if you're a human, it just verifies your computational resources.
This raises some questions. What if someone is browsing my site from an old computer? The verification will take a lot longer and possibly use all the resources that device has for minutes.
What happens to botnets? While tracking-based captchas have a chance to combat them, it doesn't really matter if hacker guy has to do some PoW on the botnet computers.
Thanks to Bitcoin, we also have really efficient sha256 ASICs - computers that only solve sha256, but they do it really efficiently. If a verification take 2 seconds on a CPU, then it will take milliseconds on an ASIC. So with just one ASIC, I'm able to essentially break any website.
Right now I think this captcha is MUCH better than not using any captcha - but I don't think it is better that the tracking based captchas. I'd be the happiest if this could work, so please prove me wrong if I didn't get it right. I also think it is really important to have experiments like this, I really support the direction.
Love this approach! π‘ Using SHA-256 proof-of-work as a CAPTCHA alternative is such a smart, elegant solution β especially in an era where user privacy and page speed really matter. πβ‘οΈ
Curious how it performs in real-world bot scenarios β any benchmarks or early adopter feedback?
Awesome work, and congrats on the launch! π
250x smaller than hCaptcha is huge for web performance. Can we modify PoW parameters per use case, like stricter thresholds for login vs. comment forms?
This is great. I will use it on my next project as it seems really straightforward and easy to implement. Congrats for the launch & good luck!
About Cap on Product Hunt
βA lightweight, modern open-source captchaβ
Cap launched on Product Hunt on April 21st, 2025 and earned 441 upvotes and 33 comments, earning #2 Product of the Day. Cap is a lightweight, modern open-source CAPTCHA alternative designed using SHA-256 proof-of-work and JS instrumentation. It's: - β‘οΈ 250x smaller than hCaptcha - ποΈ Private - π Fully customizable - π€ PoW-based - π³ Fully FOSS - π¨ Invisible
Cap was featured in User Experience (364.7k followers), Developer Tools (511k followers), GitHub (41.2k followers) and Tech (621.5k followers) on Product Hunt. Together, these topics include over 275.8k products, making this a competitive space to launch in.
Who hunted Cap?
Cap was hunted by tiago. A βhunterβ on Product Hunt is the community member who submits a product to the platform β uploading the images, the link, and tagging the makers behind it. Hunters typically write the first comment explaining why a product is worth attention, and their followers are notified the moment they post. Around 79% of featured launches on Product Hunt are self-hunted by their makers, but a well-known hunter still acts as a signal of quality to the rest of the community. See the full all-time top hunters leaderboard to discover who is shaping the Product Hunt ecosystem.
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