Many [tag]web developers[/tag] (particularly good ones) now code to standards laid out by the [tag]W3C[/tag]. There are many reasons to do this including faster page rendering times, more easily maintainable code and improvements in [tag]accessibility[/tag]. But does coding in well formed, valid markup make any difference to [tag]search optimisation[/tag]/[tag]search ranking[/tag]?

The official line (or nearest thing to it) is that valid pages are "generally" treated no differently to invalid ones. In this video from Matt Cutts (Go to about 2:40 in the video) he discusses the topic of valid markup in some detail and whilst he's not completely black and white on the subject, Matt does give the impression that valid markup is not given special attention and is not currently used as a "signal" citing a report created by Inktomi co-founder [tag]Eric Brewer[/tag] which estimates that at least 40% of the pages on the web have syntax errors. With this error rate search engines simply could not afford to discriminate against bad markup - how would Amazon and MySpace ever get anywhere (aside of course from thier massive link power);-).

That said, there are some real [tag]SEO[/tag] benefits to coding with valid markup:

1. Indexability

   The first part of the marathon that is an SEO campaign is getting web pages into a search engines index - this needs to happen before a page can rank at all. All things considered equal, it will be easier and quicker for a search engine bot to crawl valid, error free markup than it will be to crawl a page full of syntax errors. Syntax errors could also stop the bots from getting deeper into your site resulting a partial index of your pages.

2. Keyword placement

   Generally speaking, [tag]valid markup[/tag] (especially when paired with good [tag]css[/tag]) is very lightweight - the code to content ratio is going to be lower than if you have some awful WYSIWYG code that uses nested tables, font tags and other nasties. Valid markup and layouts created with <div>'s and css are often associated with source ordered content. Both of these facts mean that potential keywords will be nearer to top of the page and therefore be more relevant in [tag]search ranking[/tag] terms. Its important to note that these facts are by-products of valid markup and do not occur as a direct result of clean code.

3. Keyphrase emphasis

   Generally - valid markup also means [tag]semantically correct markup[/tag]. In other words you are going to naturally be using more of the html tags (such as headings and lists) that search engines give priority to when ranking a page. Sure you can still use these tags in invalid markup but its more likely that you will use them (and in greater frequency) when producing valid, semantically correct code.

4. Less chance of error

   The very fact that a page validates means that all but the most obscure of syntax errors will not be present. Consider invalid markup such as this:

   <p><b some really relevant and highly important keywords</b></p>

   The fact that the closing angle bracket is missing from the opening bold tag means that search engine bots will interpret this content as html attributes and probably not index the words at all. Browsers will still render the markup above with differing results. Validating markup eliminates 99% of these errors. And - yes pedants, those should have been <strong> tags and not deprecated <b> tags!

So go ahead and validate your pages today - it might just be worth it!