When creating HTML code for a website, you need to be sure that it is well formed, correct, and SEO-friendly. Make sure that you close all the tags so that search engines can easily crawl through your website. Broken tags create problems for search engines. Search engine spiders are just computer programs with predefined, preprogrammed set of rules. If a web page does not fulfill those rules, the search engine will not read the page content properly. This can be a serious problem for website owners. SEO-friendly HTML are almost W3C validated HTML.