LiveValidation is a small open source javascript library for making client-side validation quick, easy, and powerful. It comprises of two main parts. Firstly, it provides developers with a rich set of core validation methods, which can also be used outside the context of forms. Secondly, it provides your visitors with real-time validation information as they fill out forms, helping them to get it right first time, making the forms easier, quicker and less daunting to complete.

The naming conventions and parameters of the validations are similar to those found in the Ruby on Rails framework, and as such is the perfect client-side companion. Don’t worry if you dont use Ruby on Rails though, LiveValidation can be used anywhere you like, is simple to learn, and a joy to use.

Two versions are provided - a prototype.js version (ideal for use with Rails), and a standalone version (for using with any other javascript framework, or when having one at all would be overkill). Both are fully tested on most modern browsers with a comprehensive test suite.

So take a look around, download it, and make some forms (for) fun!

Check this out : LIVEVALIDATION.com