Enter your website address and select various validation, checks etc through one website. by Uitest.com

This tool will produce an immediate report on a single Web page.A "Standard" report will present only errors, but will still have the longer commentary. An "Expert" report will only list elements that might contain problems, with terse error messages. by Doctor-html.com

This is the W3C Markup Validation Service, a free service that checks Web documents in formats like HTML and XHTML for conformance to W3C Recommendations and other standards. . by Validator.w3.org

Look for free email address providers here. This tool is intended to help you reduce credit card fraud by checking if an email account is a known free email account. by Ranks.nl

Validate XML by entering URL or pasting in some XML . by Virtualpromote.com

Enter a url and submit to have this nice tool review the given url and check the html. It will present by Htmlvalidator.com

a free service that checks Cascading Style Sheets (CSS) in (X)HTML documents or standalone for conformance to W3C recommendations. by W3.org

This is a validator for syndicated feeds. It works with RSS 0.90, 0.91, 0.92, 0.93, 0.94, 1.0, and 2.0. It also validates Atom feeds.To use it, simply enter the address of your feed and click Validate. by Feedvalidator.org