How Do Search Engines Work? 

Have you ever found yourself mystified by the power of Google and wondered how search engines work? We are here to explain! In this guide, we will give you an introduction to how search engines work and specific information for the most popular search engines. 

Three Primary Functions of Search Engines

Search engines work through three primary functions: crawling, indexing, and ranking.

Crawling is the process of looking through the internet for content and looking over the code/content for each URL they find. Indexing is the storing and organizing of the content found during the crawling process. Once a page is in the search engine index, it is in the running to be displayed as a result of relevant queries. Ranking is when the search engine provides the pieces of content that will best answer a searcher’s query. This means that the results are put in order from most relevant to least relevant. 

search engines

What is Search Engine Crawling? 

Search engines work by searching hundreds of billions of pages using their own website crawlers. These website crawlers are often known as “search engine bots” or “spiders.” Search engines navigate the web by downloading web pages and following links on these pages to discover new pages that have been made available. 

What is a Search Engine Index? 

Webpages that have been discovered by the search engine are added into a data structure called the search engine index. In this index, there are all the known and discovered URLs along with a number of relevant key signals about the content that is inside each URL, such as: 

  • Keywords discovered within the page’s content – what topics do the page cover? 
  • The type of content that is being crawled – what is included in the page? 
  • The freshness of the page – how recently was it updated?
  • The previous user engagement of the page and/or the domain of the page – how do people interact with the page?

Why Might a Page Not Be Indexed? 

There are a number of factors that can lead to a URL not being indexed by a search engine. One of the reasons for this is robots.txt file exclusions, which is when a file tells search engines that they shouldn’t visit your site. There could also be directives on the webpage telling search engines not to index that page or to index another similar page. The search engine algorithm could judge the page to be of low quality, have thin content, or contain duplicate content. The final reason is that the URL returns an error page or has a 404 not found HTTP response code. 

search engine optimization

What is the Purpose of a Search Engine Algorithm? 

A search engine algorithm presents a relevant set of high-quality search results that will fulfill the user’s question or entry as quickly as possible. The user selects an option from the list of search results. This action, along with activity, then feeds into future learnings which can affect search engine rankings going forward. 

What Happens When a Search is Performed? 

When a search inquiry is entered into a search engine by a user, all of the pages which are deemed to be relevant are identified from the index and an algorithm is used to determine each website’s search engine rankings. The algorithms used to rank the most relevant results differ for each search engine. For example, a page that ranks highly for a search query in Google may not rank as high in other pages such as Bing or Yahoo. 

In addition to the search reentry, search engines use other relevant data to return results including: 

  • Location: some results are location-dependent, such as ‘cafes near me’ or ‘movie times’. 
  • Language detected: some search engines will return results in the language of the user, if it can be detected. 
  • Previous search history: search engines will return different results for a result dependent on what the user has previously searched for. 
  • Device: a different set of results may be returned based on the device from which the question was made. 

Breaking Down Search Engine Algorithms by Platform

Every search engine goes about surfacing search results in a different way. Here are the top four platforms in today’s market and how they make decisions about content quality and relevancy. 

website search engine ranking

1 – Google Search Algorithm 

Google is one of the most popular search engines in the world. Did you know that their search engine routinely own over 90% of the market, resulting in approximately 3.5 billion individual searches on their platform every day? That is a lot of people and a lot of searches. When someone performs a search, Google looks at these five major factors: 

  1. Query meaning: This determines the intent of any end user’s question. Google uses this to determine exactly what someone is looking for. 
  2. Web page relevance: Once Google has determined the intent of a search query, they review the content of ranking web pages to figure out which one is the most relevant. 
  3. Content quality: With the keywords matched, Google takes it a step further and reviews the quality of the content on the requisite web pages. This type of search engine optimization helps them prioritize which kind of results come first by looking at how worthy a website is as well as its page rank and freshness. 
  4. Web page usability: Google gives website search engine ranking priority to websites that are easy to use. 
  5. Additional context and settings: this tailors searches to past user engagement and specific settings within the Google platform. 

2 – Bing Search Algorithm 

Bing is Microsoft’s main search engine, which uses an open-source vector-search algorithm called the Space Partition Tree (SPTAG) to surface results. This means they are going in a totally different direction from Google’s keyword-based search. Bing has two separate modules – index builder and searcher. Index builder is the code that works to categorize website information into vectors. Searcher is the way that Bing makes connections between search queries and vectors in their index. 

Instead of a keyword-first model like Google, Bing breaks down information into individual data points called vectors. A vector is a numerical representation of a concept and this concept is the basis for Bing’s search structure. 

Search queries for Bing are based on an algorithm principle called Approximate Nearest Neighbor, which uses deep learning and natural-language models to provide faster results based on the proximity of certain vectors to one another.

how do search engines work

3 – DuckDuckGo Algorithm 

DuckDuckGo works a little bit differently in the search engine market. While they have a web crawler called DuckDuckBot to scour web-page content, a lot of their information shows on their results page from over 400+ different third-party sources, such as Bing, Yahoo, and Wikipedia. 

DuckDuckGo doesn’t capture personal information on their users, including past search history and IP addresses. This dedication to privacy makes their algorithm work harder than others. DuckDuckGo also allows users to use custom parameters called bangs to bypass the search results entirely. DuckDuckGo then acts as a search portal for platforms such as Wikipedia, Amazon, and Twitter. 

4 – YouTube Search Algorithm 

YouTube is the most popular video-hosting website. Their search engine runs on similar rules to Google, which owns the platform. It focuses on search engine optimization keywords and relevancy. The algorithm is further broken down into two separate functions: ranking videos in search and surfacing relevant recommendations. 

Videos rank higher on Youtube because Youtube tends to lean towards the newness of the video and the frequency of channel uploads being the most important factors. There are three main priorities of Youtube: 

  • Scale: Over 300 hours of videos are uploaded to YouTube every minute, and the platform has over 1.3 billion users. 
  • Freshness: YouTube balances how they recommend videos based on how recently a video was uploaded as well as an individual’s past behavior. 
  • Noise: Due to the amount of content that people watch, it is difficult for any AI to parse what is the most relevant at any time. 

In order to rank well on YouTube, you have to have a solid profile and also consistent uploads. Their focus on popularity and profile strength takes more investment from marketers but pays off for brands that focus their efforts on the platform. 

Knowing How Search Engines Work Helps You Create Better Content 

Knowing how different platforms display their results makes it easier to create content with the potential to rank well. This understanding also helps you diagnose why certain types of content rank either better or worse than others. You can create your content using search engine optimization principles to improve your website’s search engine ranking and traffic. It all comes down to knowing your customer well enough so that your content can rank well. If you need more information when it comes to creating content that will rank well, reach out to SEO Design Chicago today! 


  • What three primary functions do search engines have?
  • What is search engine crawling?
  • How do search engine algorithms differ from platform to platform?
  • What is a search engine index?
  • Why is knowing how search engines work so important?

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