diff --git a/4.1-Extensions.md b/4.1-Extensions.md
index 5e9d68a..a8b57cb 100644
--- a/4.1-Extensions.md
+++ b/4.1-Extensions.md
@@ -43,6 +43,8 @@ These are all, where applicable, best configured to `deny-all` and whitelist.
 
 * [uBO-Scope](https://addons.mozilla.org/firefox/addon/ubo-scope/) | [GitHub](https://github.com/gorhill/uBO-Scope)
 * [Detect Cloudflare](https://addons.mozilla.org/firefox/addon/detect-cloudflare/) | [GitHub](https://github.com/traktofon/cf-detect) | [claustromaniac's fork](https://github.com/claustromaniac/detect-cloudflare-PA)
+* [Compare-UserJS](https://github.com/claustromaniac/Compare-UserJS)
+   * Not an extension, but an excellent tool to compare user.js files and output the diffs in detailed breakdown - by our very own incomparable [claustromaniac](https://github.com/claustromaniac) :cat2: 
 
 ### :small_orange_diamond: Don't Bother...
 * Ghostery, Disconnect, Privacy Badger