How Do Search Engines Work?

How Search Engines Work

Search engines are the most important resource on the Internet. We would be lost without them. Google, Bing, and Yahoo! are responsible for over 95% of all searches online. There are also many smaller niche search engines. This article explains how search engines work.

All search engines have a few things in common.


Search engines acquire data by crawling websites to get a complete list of all their content. Search engine spiders and bots extract the content and keywords, titles, and images of documents as they visit each webpage and crawl through the embedded URLs. Some crawlers read thousands of pages per second, which can require an enormous amount of network bandwidth and computing resources. For example, Google and Bing both have thousands of servers in data centers around the world which are constantly crawling, indexing, and updating web pages. Webmasters can see evidence of crawlers having visited by looking at log files, where records containing Googlebot and Bingbot may be found.


Indexing documents is arguably the most important and the most difficult step. The billions of documents that search engine crawlers download must be efficiently indexed into a large distributed database so that search queries can lookup information and return results. Before the documents can be indexed, they must be inspected for spam, keyword stuffing (pages full of nonsensical keywords), malicious links, viruses and more. The indexing system must also analyze the document to determine the type of content, the subject matter and then properly index the document in the right category, so search results are as accurate as possible.

Ranking & Search Result Retrieval

The final step? The results users see when they type a query and the search engine displays the most relevant documents for the request. During this step, the search engine simultaneously connects to tens, hundreds or even thousands of computers which have unique indexes of keywords linked to billions of relevant documents. Then it aggregates the results to provide the most relevant documents for the query.