...Request the same production resources and test the actual behavior of your app. Augment an existing API, or design it as you go, when there is none. Use Express-like routing syntax to capture outgoing requests. Parameters, wildcards, regular expressions, mocking has never been easier. Browser usage is what sets Mock Service Worker apart from other tools. Utilizing the Service Worker API, which can intercept requests for the purpose of caching, Mock Service Worker responds to captured requests with your mock definition on the network level. This way your application knows nothing about the mocking.