CSS Selector Tester is a free Chrome add-on developed by simondev. As an add-on in the Browsers category, it falls under the subcategory of Add-ons & Tools. This program is designed to make it easy for users to validate their CSS selectors visually.

With CSS Selector Tester, users can easily identify elements that match a given CSS selector. The tool highlights elements in real-time as you type, making it simple to see the results instantly. Additionally, it provides the total number of matches based on the selector, allowing users to quickly assess the effectiveness of their selector.

The interface of CSS Selector Tester is clean, simple, and intuitive to use. It offers a seamless experience for web designers or those involved in web scraping. However, it's important to note that this extension currently does not support the "HTML" Element or the "*" selector.

Overall, CSS Selector Tester is a useful tool for validating CSS selectors visually. Its real-time highlighting feature and clear interface make it a valuable resource for web design and web scraping tasks.