A complete JavaScript implementation of the standard can be found at jsdom/whatwg-url. This implementation is kept synchronized with the standard and tests.
A complete C++ implementation of the standard can be found at ada-url/ada. This implementation is kept synchronized with the standard and tests, and is currently used in Node.js.
The Live URL Viewer lets you manually test-parse any URL, comparing your browser's URL parser to that of jsdom/whatwg-url.