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How Search Engines Work

Search Engines are programs that search an index of the world wide web for keywords and display the results in order. They find and rank web content matching a user’s search query.

Examples of popular search engines include Google, Bing, and DuckDuckGo.

How Search Engines Work

According to InternetLiveStats, Google receives an average of 5.5 billion searches a day. Or 63,000 searches per second. For every one of those queries, the search engine trawls through more than 130 trillion individual pages internet-wide and selects the fitting results in less than a second.

Behind those results lies a lot of groundwork. While Google, like other search engines, is notoriously secretive about the mechanisms behind search results, marketers benefit from knowing how search engines work. Understanding how search engines find, organize, and select results means you can better optimize your web pages to rank. Let’s get you informed.

A search engine is an interlinked network system that works together to identify pieces of web content, including images, videos, and website pages, based on the words you type into a search bar. Site owners use Search Engine Optimization to improve the chances that content on their site will show up in search results.

Search engines use three basic mechanisms:

  • Web Crawlers
  • Search index
  • Search Algorithms

How Search Engines Crawl, Index, and Rank Content

From the outside, Search engines look simple. You type in a keyword, and you get a list of relevant pages. But that deceptively easy interchange requires a lot of computational heavy lifting backstage.

The hard work starts way before you make a search. Search engines work round-the-clock, gathering information from the ever-growing list of websites and organizing that information, so it’s easy to find. This is a three-step process of first crawling web pages, indexing them, then ranking them with search algorithms.


Search engines rely on crawlers to scour the web for information. Crawlers start out with a list of websites. Algorithms, sets of computational rules, automatically decide which of these sites to crawl. The algorithms also dictate how many pages to crawl and how frequently.

Crawlers visit each site on the list systematically, following links through tags to jump to internal or external pages. Over time, the crawlers build an ever-expanding map of interlinked pages. It is critical for you to make sure your site is easily accessible to crawlers. If your site is not accessible to Search engines, Technical SEO services from Clickslice are at your disposal to ensure that search engines can crawl your site. If bots can’t crawl it, they can’t index it, and that means your site won’t appear in search results.

If you’re not sure whether your site is accessible to crawlers, check it out on a Site Audit tool. The tool catches accessibility issues and advises on how to fix them.


After finding a page, a bot renders it similar to the way your browser does. That means the bot should see what you see, including images, videos, or other types of dynamic page content.

The bot organizes this content into categories, including images, HTML, text, and keywords. This process allows the crawler to understand what’s on the page, a necessary precursor to deciding for which keyword searches the page is relevant.

Search engines then store this information in an index, a giant database with a catalogue entry for every word seen on every webpage indexed. Google’s index, the Caffeine Index, takes up around 100,000,000 gigabytes and fills server farms. These farms are thousands of computers that never get turned off, around the globe.

If you want to know what crawlers see when they land on your site, use the URL Inspection Tool. You can also use the tool to find out why crawlers aren’t indexing the page or request that Google crawl it. Use a robots.txt file to control access by telling bots which pages they can crawl.


In the final step, search engines sort through indexed information and return the right results for each query. They do that with search algorithms, rules that analyze what a searcher is looking for and which results best answer the query.

Algorithms use numerous factors to define the quality of the pages in their index. Google leverages a whole series of algorithms to rank relevant results. Many of the ranking factors used in these algorithms analyze the general popularity of a piece of content and even the qualitative experience users have previously had when they land on the page

To make sure that the algorithms are doing their job properly, Google uses human Search Quality Raters to test and refine the algorithm. This is one of the few times when humans, and not programs, are involved in how search engines work.

How Search Engines Personalize Results

Search engines understand that different results appeal to different people. That’s why they tailor their results for each user.

If you’ve ever searched for the same thing on multiple devices or browsers, you’ve probably seen the effects of this personalization. Results often show up in different positions depending on various factors.

It’s because of this personalization that if you’re doing SEO, it is better to use a dedicated rank tracking tool to track ranking positions. Your search results are personalized according to your:

  • Language
  • Location
  • Search History

Understanding how search engines work is the first step towards ranking higher in Google and getting more traffic. If search engines can’t find, crawl and index your pages, you’re dead in the water before you even start.

The best way is to begin by optimizing your website for SEO. Sending the right signals to search engines guarantees that your pages appear in results pages relevant to your business. Serving up to searchers, and search engines, the content they want is a step along the path to a successful online business.

Article by:

Joshua George is the founder of ClickSlice, an SEO Agency based in London, UK.

He has eight years of experience as an SEO Consultant and was recently hired by the UK government for SEO training. Joshua also owns the best-selling SEO course on Udemy, and has taught SEO to over 100,000 students.

His work has been featured in Forbes, Entrepreneur, AgencyAnalytics, Wix and lots more other reputable publications.

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