diff --git a/README.md b/README.md
index 37cc9e4..e554eaf 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,9 @@ A local web app for building and reusing prompt templates. Write a prompt once w
 
 ![prompt-gen screenshot](https://shx.reversed.dev/u/dspbfv.png)
 
+> [!WARNING]
+> **Do not expose this app to the public internet.** There is no authentication — anyone who can reach the server can read, modify, and delete your presets, and access your stored OpenAI API key. Run it on localhost or behind a private network/VPN only.
+
 ## Features
 
 - **Presets** — save any number of named templates with descriptions