diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b65d57db..d4fa38cf 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -7,12 +7,15 @@
 
 2. Use JetBrains annotations
 - Every parameter should be annotated with @NotNull or @Nullable
-- Use @NotNull over lombok @NonNull
 
 3. Imports
 - No group (*) imports.
 - No static imports.
 
+4. Kotlin
+- Kotlin should be the only language used in the backend, java should be the only language used in the frontend.
+- Kotlin API extensions should only be for creating extension functions and extra niceties that aren't possible in java. Do not write API components in kotlin.
+
 ## Dependency Injection
 - eco uses Dependency Injection
 - Any calls to Eco#getHandler#getEcoPlugin are code smells and should never be used unless **absolutely necessary**.