The HTML Entity Encoder / Decoder is a crucial tool for web developers and content creators. HTML entities are used to display reserved characters (like `<`, `>`, `&`) or special characters that may not be available on a standard keyboard. This tool allows you to easily encode plain text into its HTML entity equivalent to prevent it from being interpreted as code by the browser. Conversely, you can decode HTML entities back into their original characters.

To Encode:

1. Select the "Encode" tab.
2. Type or paste your plain text (e.g., `<div>Hello</div>`) into the left-hand textarea.
3. Click the "Encode" button.
4. The text will be converted into HTML entities (e.g., `&lt;div&gt;Hello&lt;/div&gt;`) in the right-hand textarea.

To Decode:

1. Select the "Decode" tab.
2. Paste your HTML entity string into the left-hand textarea.
3. Click the "Decode" button.
4. The entities will be converted back to their original characters in the right-hand textarea.