Regexper. JsFiddle: An online playground for your JavaScript, HTML, CSS. JsFiddle lets developers play with the three core elements of Web development.
Check out this powerful application for rapid prototyping and testing. Every developer has been in the situation where you have code or a design that you need to test quickly and possibly share with others. jsFiddle is the perfect solution; it provides a custom environment (based on user selections) to test (or fiddle with) your JavaScript, HTML, and CSS code right inside your browser. Create a new Fiddle - jsFiddle.