How do search engines work?

The operation of a search engine can be summarized in two steps: crawling and indexing.


A search engine scours the web crawling with what are called bots. These go through all the pages through the links. Hence the importance of a good link structure. Just like any user would do when browsing the content of the Web, they go from one link to another and collect data about those web pages that they provide to their servers.

The crawl process starts with a list of web addresses from previous crawls and sitemaps provided by other web pages. Once they access these websites, the bots look for links to other pages to visit them. Bots are especially attracted to new sites and changes to existing websites.

It is the bots themselves that decide which pages to visit, how often and how long they are going to crawl that website, which is why it is important to have an optimal loading time and updated content.

It is very common that in a web page it is necessary to restrict the crawling of some pages or of certain content to prevent them from appearing in the search results. For this you can tell search engine bots not to crawl certain pages via the ” robots.txt ” file.


Once a bot has crawled a website and collected the necessary information, these pages are included in an index. There they are ordered according to their content, their authority and their relevance. In this way, when we make a query to the search engine, it will be much easier for it to show us the results that are most related to our query.

At first, search engines were based on the number of times a word was repeated. When doing a search, they tracked those terms in their index to find which pages had them in their texts, positioning the one that had it repeated the most times. Today, they are more sophisticated and base their ratings on hundreds of different things. The date of publication, if they contain images, videos or animations, microformats, etc. are some of those aspects. Now they give more priority to the quality of the content.

Once pages are crawled and indexed, it’s time for the algorithm to kick in: algorithms are the computer processes that decide which pages appear first or last in search results. Once the search is done, the algorithms check the indexes. This way they will know which are the most relevant pages taking into account the hundreds of positioning factors. And all this happens in a matter of milliseconds.

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