Koa is a free and open-source, expressive HTTP middleware framework for Node.js. Koa provides a great developer experience that makes writing web applications and APIs more enjoyable. Koa's middleware stack flows in a stack-like manner, allowing you to perform actions downstream then filter and manipulate the response upstream. Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small codebase. This includes things like content negotiation, normalization of node inconsistencies, redirection, and a few others.