The URL Pattern API enables developers to create matchers for URLs using a specific syntax. It supports features like wildcards, named groups, and regex for flexible URL matching. This API is useful for validating and extracting components from URLs in web applications.

The article explains a tool for checking the equivalence of two JavaScript regular expressions, highlighting that without start (^) and end ($) anchors, RegExp can match substrings, which may lead to unexpected results. Users can input two regex patterns, and the tool will determine if they match the same strings, providing examples of strings that match one expression but not the other when they do not. It also outlines supported and unsupported syntax features for the regex checks.