# 18. Commenter

> For the complete documentation index, see [llms.txt](https://plugins.jetbrains.com/docs/intellij/llms.txt).

> **TL;DR**
> Reference: [Comment Code](additional-minor-features.html#comment-code)
>
>
>
> Code: [SimpleCommenter](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCommenter.java)
>
>
>
> Testing: [9. Commenter Test](commenter-test.html)

> **Tip:**
> This page is part of multi-step [Custom Language Support Tutorial](custom-language-support-tutorial.html). All previous steps must be executed in sequence for the code to work.

A commenter enables the user to comment-out a line of code at the cursor or selected code automatically. The [Commenter](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/lang/Commenter.java) defines support for `Code | Comment with Line Comment` and `Code | Comment with Block Comment` actions.

## Define a Commenter

The [SimpleCommenter](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCommenter.java) for Simple Language defines the line comment prefix as `#`.

```JAVA
final class SimpleCommenter implements Commenter {

  @Override
  public String getLineCommentPrefix() {
    return "#";
  }

  @Override
  public String getBlockCommentPrefix() {
    return "";
  }

  @Nullable
  @Override
  public String getBlockCommentSuffix() {
    return null;
  }

  @Nullable
  @Override
  public String getCommentedBlockCommentPrefix() {
    return null;
  }

  @Nullable
  @Override
  public String getCommentedBlockCommentSuffix() {
    return null;
  }

}
```

## Register the Commenter

The `SimpleCommenter` implementation is registered in the plugin configuration file using the [com.intellij.lang.commenter](https://jb.gg/ipe?extensions=com.intellij.lang.commenter) extension point .

```XML
<extensions defaultExtensionNs="com.intellij">
  <lang.commenter
      language="Simple"
      implementationClass="org.intellij.sdk.language.SimpleCommenter"/>
</extensions>
```

## Run the Project

[Run](creating-plugin-project.html#running-the-plugin) the plugin.

Open the example Simple Language [properties file](lexer-and-parser-definition.html#run-the-project) in the IDE Development Instance. Place the cursor at the `website` line. Select `Code | Comment with Line Comment`. The line is converted to a comment. Select `Code | Comment with Line Comment` again, and the comment is converted back to active code.

![Commenter](images/commenter.png)