Keeping your code properly written can make the difference between a visitor loading your page
correctly and a visitor getting a mess that their browser can't display. In
this case, we are counting both people and search-engine spiders under the
category of 'visitor'. Poor code can also prevent search-engine spiders and bots
from reading and indexing your page.
W3C has two tools that can help you ensure your pages are up to scratch:
You can find the CSS Validator here.
And you can find the HTML Validator here.
Sure, we know that search engines, for the most part, can only read text. But what would that look like? Below are two tools that
help you see your site for the text it is. Remember, if it doesn't look good
here, it probably won't look so great in the indexes either! If you can't read
and navigate the bulk of your site with these two tools, then you should take a
very serious look at how your site is put together.
http://www.seo-browser.com/
To use the next one, just do a whois on your domain name
(http://www.yoursite.com), and when the results come up take a look at the Site
Profile tab. It will show you a preview of how it looks to the search-engine
spiders, with a link to surf your site in a text browser. This is a very useful tool.
http://www.domaintools.com/