Back when we had only ASP, developers who had to write webpages for forms knew that the most tedious part is writing code to validate the user input. User input had to be validated so that malicious use of the pages couldn't be achieve. User input had to be validated so that an incorrect piece of information would not be entered. User input had to be validated so that the information stored was standardized. Yeah, some people had libraries of ASP functions to validate common things such as postal codes (zip codes for you Americans), e-mail addresses, phone numbers, etc. The developers of ASP.NET saw the tedium in always having to check user input. They decided that to simplify our life by including validation controls.

ASP.NET validation controls also provide two ways of validation: Server-side or Client-side. The nice thing about these Validation controls is that it will preform client-side validation when it detects the browser is able (unless client-side validation has been disabled). Thus reducing roundtrips. And it will preform server-side where necessary. This client-side/server-side detection and validation is done without extra work by the developer!

With ASP.NET, there are six(6) controls included. They are:

• The RequiredFieldValidation Control
• The CompareValidator Control
• The RangeValidator Control
• The RegularExpressionValidator Control
• The CustomValidator Control