Technical SEO are optimizations related to the structure of a site. The intention is for pages to become faster, more understandable, crawlable and indexable, in order to increase the likelihood of achieving better positioning on Google.
Although the focus of Technical SEO is to demonstrate to search engines how your site performs, it is also intended to deliver the best user experience. Technical SEO is the foundation of any search engine optimization strategy, so it should be the first step in the process, along with On-Page SEO.
