diff --git a/functions/helloworld/index.js b/functions/helloworld/index.js
index 32ceeb4263..026450a433 100644
--- a/functions/helloworld/index.js
+++ b/functions/helloworld/index.js
@@ -20,6 +20,8 @@ const Buffer = require('safe-buffer').Buffer;
 // [START functions_helloworld_get]
 /**
  * HTTP Cloud Function.
+ * This function is exported by index.js, and is executed when
+ * you make an HTTP request to the deployed function's endpoint.
  *
  * @param {Object} req Cloud Function request context.
  * @param {Object} res Cloud Function response context.