diff --git a/docs/tone_of_voice.mdx b/docs/tone_of_voice.mdx
index 589dfb7f..7413a07a 100644
--- a/docs/tone_of_voice.mdx
+++ b/docs/tone_of_voice.mdx
@@ -53,7 +53,17 @@ Data over description - Show metrics, not marketing.
 Write complete, runnable examples with error handling, expected outputs, and realistic values (use environment variables, not placeholders).
 
 ```javascript
-const apiKey = process.env.API_KEY;
+function calculateTotal(numbers) {
+  if (!Array.isArray(numbers)) {
+    throw new Error('Input must be an array');
+  }
+  if (!numbers.every((num) => typeof num === 'number' && !Number.isNaN(num) && isFinite(num))) {
+    throw new Error('Input must contain only finite numbers');
+  }
+  return numbers.reduce((sum, num) => sum + num, 0);
+}
+
+const apiKey = process.env.API_KEY; // Use only if needed for API calls
 
 try {
   const result = calculateTotal([10, 20, 30]);