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tiagozip/cap

A privacy-first, self-hosted CAPTCHA alternative that verifies users with background proof-of-work and instrumentation challenges instead of puzzles.

Open-source alternative to:hCaptchaGoogle reCAPTCHA

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Open issues
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Last commit
8 days ago

What is it?

cap is a self-hosted CAPTCHA replacement that skips puzzles like clicking traffic lights. Instead, the visitor's browser quietly solves small challenges in the background, including GPU-resistant proof-of-work and instrumentation checks. The project is designed so no third party sees visitor data, and the challenges can be tuned to slow down autonomous AI agents that consume server resources.

The project has no dependencies by default and can be deployed with Docker, on Cloudflare Workers, or on Railway. The README states it is roughly 200 times smaller than hCaptcha and names bunny.net and AdGuard as production users.

The widget is distributed through npm packages under the @cap.js scope, including a WebAssembly build for browser-side solving.

Key features

  • 01Replaces image puzzles with background proof-of-work and instrumentation challenges.
  • 02Self-hosted, so visitor data stays on your own infrastructure.
  • 03Includes configurable challenges aimed at autonomous AI agents.
  • 04Runs with no dependencies by default.
  • 05Deployable via Docker, Workers, or Railway.

Use cases

  • Protecting login, signup, or comment forms from bots without showing puzzles to users.
  • Adding a privacy-respecting CAPTCHA to sites that must avoid third-party trackers.
  • Limiting scraping and automated abuse of public APIs or web pages.

Quick start

  1. 1

    Read the docs at trycap.dev to set it up with Docker, Workers, or Railway

Things to know

  • The README does not give install commands, so you must follow the external docs to run it.
  • The repository metadata shows no clear license, while the README states Apache 2.0, so check the LICENSE file.

Topics

#captcha#anti-bot#proof-of-work#privacy#self-hosted#anti-abuse#javascript#anti-scraper#antispam#defense

FAQ

What is cap?
A privacy-first, self-hosted CAPTCHA alternative that verifies users with background proof-of-work and instrumentation challenges instead of puzzles. cap is a self-hosted CAPTCHA replacement that skips puzzles like clicking traffic lights. Instead, the visitor's browser quietly solves small challenges in the background, including GPU-resistant proof-of-work and instrumentation checks. The project is designed so no third party sees visitor data, and the challenges can be tuned to slow down autonomous AI agents that consume server resources.
Is cap free to use? What license does it have?
cap is open source under the Other license. Check the license terms before using it in commercial products.
Is cap still maintained?
Actively maintained. The last commit to cap was on Oct 12, 2026.
What can I use cap for?
Protecting login, signup, or comment forms from bots without showing puzzles to users. Adding a privacy-respecting CAPTCHA to sites that must avoid third-party trackers. Limiting scraping and automated abuse of public APIs or web pages.
How do I install cap?
Read the docs at trycap.dev to set it up with Docker, Workers, or Railway
Where can I get cap?
The source code and installation instructions are on GitHub: https://github.com/tiagozip/cap

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