diff --git a/.env.example b/.env.example
index fa1a469..ca9ba6e 100644
--- a/.env.example
+++ b/.env.example
@@ -1,6 +1,2 @@
-# Do not share your OpenAI API key with anyone! It should remain a secret.
+# see process.d.ts 
 OPENAI_API_KEY=YOUR_OPENAI_API_KEY
-# Optional.
-# OPENAI_API_ENDPOINT=YOUR_OPENAI_API_ENDPOINT
-# USAGE_DATABASE_URL=postgresql://USER:PASSWORD@HOST:PORT/DATABASE?schema=sqlchat_usage
-# NEXT_PUBLIC_API_KEY=YOUR_API_KEY
diff --git a/process.d.ts b/process.d.ts
new file mode 100644
index 0000000..dfc23c4
--- /dev/null
+++ b/process.d.ts
@@ -0,0 +1,13 @@
+declare namespace NodeJS {
+  export interface ProcessEnv {
+    // Required. Do not share your OpenAI API key with anyone! It should remain a secret.
+    OPENAI_API_KEY: string;
+    // Optional. OpenAI API endpoint. Defaults to https://api.openai.com.
+    OPENAI_API_ENDPOINT: string;
+    // Optional. Database connection string to store the usage data.
+    USAGE_DATABASE_URL: string;
+    // Optional. API key to protect the backend API endpoint.
+    // This needs to be exposed to the frontend and must be prefixed with NEXT_PUBLIC_.
+    NEXT_PUBLIC_API_KEY: string;
+  }
+}