Cat BrowserOpen-source licenses
Last updated: 2026-11-06
Cat Browser is built on open-source software. We thank its authors.
Mozilla Public License 2.0
Cat Browser contains files from Brave (brave-core, adblock-rust, adblock-resources) and certifi that are subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, you can obtain one at https://mozilla.org/MPL/2.0/.
Source Code Form: the original sources are available at the project links below. The Source Code Form of the MPL-covered files as distributed in Cat Browser, including our modifications, is available on request from [email protected] at no charge beyond the cost of distribution.
GNU General Public License v3
The uBlock Origin resources and the EasyList/EasyPrivacy lists are distributed under the GPL v3 (EasyList is also available under CC BY-SA 3.0). They are distributed in source form, unmodified, as published by their authors. Copyright © Raymond Hill and contributors; © The EasyList authors. These works come with ABSOLUTELY NO WARRANTY; see the license text.
In the app
| Component | License | Notes |
|---|---|---|
| Chromium | BSD-3-Clause | Browser engine. Chromium bundles many third-party components; their notices are shown in the app at chrome://credits. |
| Brave browser core (brave-core) | MPL-2.0 | Privacy features, Shields and browser UI that Cat Browser modifies. |
| adblock-rust | MPL-2.0 | Filter-list engine behind Shields. |
| WireGuard Android tunnel library | Apache-2.0 | Cat VPN tunnel (with wireguard-go, MIT). |
| wireguard-go | MIT | Userspace WireGuard implementation (libwg-go). |
| yt-dlp | Unlicense | Video extraction on the device and on our server. |
| Chaquopy | MIT | Python runtime bridge for on-device video extraction. |
| CPython | PSF-2.0 | Python interpreter used by the on-device extractor. |
| OpenSSL | Apache-2.0 | TLS library used by the embedded Python runtime and the torrent engine. |
| jlibtorrent | MIT | Java bindings of the torrent engine (version 2.0.15.3, by FrostWire). |
| libtorrent (rasterbar) | BSD-3-Clause | BitTorrent engine of the torrent client (version 2.0.15). |
| Boost C++ Libraries | BSL-1.0 | C++ libraries built into the torrent engine. |
| certifi | MPL-2.0 | CA certificate bundle for the embedded Python runtime. |
Filter and Safe Mode lists
| Component | License | Notes |
|---|---|---|
| uBlock Origin (scriptlets, redirect resources, filter lists) | GPL-3.0 | Resources mirrored from the official releases and served unmodified. |
| Brave adblock-resources | MPL-2.0 | List catalog and resources used by Shields. |
| EasyList / EasyPrivacy | GPL-3.0 / CC BY-SA 3.0 | Ad and tracker filter lists (dual-licensed). |
| StevenBlack/hosts | MIT | Safe Mode categories (adult, gambling). |
| The Block List Project | Unlicense | Safe Mode categories (adult, gambling, phishing, scam, fraud, malware, ransomware). |
| Blacklists UT1 – Université Toulouse Capitole | CC BY-SA 4.0 | Safe Mode categories (adult, gambling, malware, phishing). |
| Phishing.Database | MIT | Safe Mode harmful-site category. |
| OISD NSFW | See project terms | Safe Mode adult category. |
| malware-filter (URLhaus hosts) | See project terms | Safe Mode harmful-site category. |
Proprietary SDKs in the app (not open source)
| Component | License | Notes |
|---|---|---|
| AppsFlyer Android SDK | Proprietary | Install attribution SDK. Not open source; used under the AppsFlyer terms of use. |
| Google Mobile Ads SDK, User Messaging Platform, Firebase, Google Play Billing | Proprietary | Ads, consent, messaging and in-app purchase SDKs from Google. Not open source; used under the Android Software Development Kit License / Google APIs Terms of Service. |
On our servers (not distributed)
| Component | License | Notes |
|---|---|---|
| SearXNG | AGPL-3.0 | Powers Cat Search. We run the unmodified official image (version 2026.11.5-3e95f6cd2) with our own settings. |
| Node.js | MIT | Runtime of our API server. |
| FFmpeg | LGPL-2.1 / GPL-2.0 | Video processing on our server. |
Trademarks
“WireGuard” and the WireGuard logo are registered trademarks of Jason A. Donenfeld. Chromium is a trademark of Google LLC. Brave is a trademark of Brave Software, Inc. Cat Browser is not affiliated with or endorsed by these projects.