Difference asp.net web service and Ihttphandler -

Simple tasks such as AJAX requests, pass a parameter and can be done with return results, web service and IHttpHandler Where ASP.NET Web Services is actually a type of HTTP handler which provides an XML-based communication. Infrastructure based on W3C standards (SOAP / WSDL) means that non NET clients can interoperate with ASP.NET web services. In your case where you are requesting a very simple single ajax to return a simple result, ASP.NET / XML Web services may overwhelm.

This simple custom may be more beneficial / efficient than implementing all the plumbing and upper part associated with ASP.NET web services, with HTTP handler custom HTML handler, you send only that parameter Which you need, and the way you want to see any support without SOAP xml, which will be created when using XML web services.