A real interval is a set of all real numbers between two endpoints. Endpoints can be finite or infinite, and the interval with negative and positive infinity endpoints is the entire real line. Intervals that do not contain their endpoints are open and ones that contain them are closed. Real interval is the fundamental concept of calculus for having a natural property "length" that can be generalized into the concept "measure" used in integration. Wolfram|Alpha has the ability to recognize the type (topology) of the given interval and to compute the other properties. Comparison between different intervals is also supported.