diff --git a/README.md b/README.md
index 51b0069..0d9a3ca 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,9 @@
 Rate limiting middleware for [Hono](https://hono.dev/). Use to
 limit repeated requests to public APIs and/or endpoints such as password reset.
 
+> [!WARNING]  
+> The `keyGenerator` function is currently under construction and needs to be defined for `hono-rate-limiter` to work properly in your environment. Please ensure that you define the `keyGenerator` function according to the documentation before using the library.
+
 ## Usage
 
 ```ts