CatBlock - An ad-blocking extension (with an ability to replace ads by pictures) for all major desktop browsers!
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Build Status Codacy Badge GPL v3


CatBlock (previously known as "AdBlock with CatBlock") is like an ad blocking extension, but instead of blocking ads it shows you pictures of cats by default (configurable).

You can also disable replacing ads by cats, so CatBlock can work as a standard ad blocking extension (useful for when you're doing presentations anywhere!)

If you want to find out the history of this extension, you can check it out here.


This project aims at maintaining and improving the original CatBlock project by Michael Gundlach (the creator of AdBlock and CatBlock), which is built on top of the AdBlock code.

AdBlock has recently switched to the Adblock Plus codebase in version 3.0, but instead of importing those changes to CatBlock, we think it would be better to improve the original codebase.


CatBlock is available in Chrome Web Store, Opera Extensions Store and Firefox Addons Store.

Right now, CatBlock is not available in the Safari Extensions Store, or in the Windows Store, but we are looking into releasing CatBlock there as well!

If you can't wait for an official release of CatBlock on Windows Store, find out how to sideload CatBlock on Edge right now.

Supported browsers

CatBlock is compatible with following browsers:

  • Chrome: 49+
  • Opera: 35+
  • Safari: 6+
  • Firefox: 48+
  • Edge: Windows 10 Anniversary - version 1607

Tools we use

We use many different services to help keep CatBlock working! We use Travis to build new versions automatically for us.

We also have Travis connected to BrowserStack, to run a few automated unit tests for us. If "builds:passing" shows at the top of this README, then it's probably working fine, otherwise the current version of the code might not work so well.


How to build the extension or create a development environment?

The development guide will make your life easier if you need to build CatBlock or create an unpacked development environment and change the source code.

Do you want to contribute?

If you want to contribute any improvements to the code, please go ahead and send us a pull request from a fork of this repo!

If we see that you are a dedicated contributor, we may provide you with contributor permissions. The people to contact for this project are @kpeckett and @tomasko126.

Do you want to know more about our project?

If you want to keep an eye on CatBlock or even know more about it, check out our Wiki page, where you can find all important information.

Get in touch with us


We have a public Discord server! Ask for help, help out with development and just chat about stuff! Join the community at This link