diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c5b0243..76b9c86 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -32,8 +32,8 @@ The following packages need to be installed on the system in order for the build
 Optional dependencies:
 
 * `codespell`
-* `lychee`
-* `epubcheck`
+* `lychee`: [Installation](https://lycheeorg.github.io/docs/#installation)
+* `epubcheck`: [Installation](https://www.w3.org/publishing/epubcheck/docs/installation/)
 
 The below examples show how to use it with a book named `book`.