diff --git a/doc/API.md b/doc/API.md
index de904ee..00628a9 100644
--- a/doc/API.md
+++ b/doc/API.md
@@ -69,9 +69,9 @@ console.log('eruda');
 Add tool.
 
 ```javascript
-eruda.add(eruda.Tool.extend({
+eruda.add(new (eruda.Tool.extend({
     name: 'test'
-}));
+})));
 ```
 
 ## remove