With Rack, application programming interfaces (APIs) for web frameworks and middleware are wrapped into a single method call handling HTTP requests and responses.

[2] Rack has inspired similar frameworks in JavaScript[3] (jack.js), Clojure,[4] Perl (Plack), Common Lisp (Clack),[5] and .NET (OWIN).

The rack server object returns a response which contains three parts: the status, headers and the body.

Rack makes it easy to add a chain of middleware components between the application and the web server.

The Rack server adds multiple middle middleware by default for the functionalities like showing exception with all the details,[8] validating the request and responses according to the Rack spec[9] etc.