Make Sure Your Website is Error Free With Online Validators

Each webpage validator seems to have a different specialty so I tend to test at more than one place if I'm not sure. I would take what they say with a grain of salt however, many of the "errors" they find are perfectly OK in all browsers. With that said though, the reason for web standards is so that in the future your pages will still look exactly as you want them, what works now may not later. Personally I tend to try my hardest to make sure any page I create validates.

WDG HTML Validator
A rather flexible validator with friendly, understandable error messages, support for different character encodings, and (I like this part!) the ability to spider an entire site and test a page before you upload it to your site! This is one of the ones I use.

W3C Validator
This one is brought to you by the big boys of website coding :) Again, it lets you validate files that are either already online, or files on your computer so you can see if they're OK before you upload. They also offer validation support for XHTML 1.1, XHTML Basic 1.0, and MathML 2.0, as well as a cascading style sheet (css) validator. Another one of the ones I use.

CSS Check
Either check a Cascading Style Sheet that's already uploaded or one that is still on your computer for errors.

Load Time Test
Very important! While many web designers have high speed internet, a lot of visitors to your website don't. Don't forget to that your site is probably already in your cache making it appear to load faster than it really does. This site will tell you the time it takes for different connection speeds to fully load your page, as well as giving tips to help speed it up.

Dr. Watson
This one will check links (both regular and image), Analyze HTML syntax, generate word counts, spell-check non-HTML text, estimate download speeds as well as check search engine compatibility and link popularity.