Search engines visit billions of pages on the World Wide Web using web crawlers (also known as spiders or bots) following links from page to page. The discovered pages are then added to an index that search engines pull results from for particular search queries.
In a few words the process that enables users to search and find relevant web pages using a search engine can be described as follow: A Search Engine uses bots to create a database of web content called an index, which is then employed by the search engine algorithm to retrieve the most relevant information from in response to a user search query.
- Search Engine Bot: A web crawler following links on already known pages to discover new pages on the web
- Search Engine Index: A digital library storing information about webpages
- Search Engine Algorithm: Computer program tasked with matching results from the search index with search queries
- User Search Query: A user input (text, image or voice) instructing the search engine about the subject of their search
Although every search engine aims to provide the most relevant search results to its users, it is important to outline that they do not make any profit in doing so. Money-wise, the search engines rely entirely on paid search results that go alongside the organic search results.
Making the distinction between the two is of paramount importance. This description of how search engines work including the said search engine bots, the index and the algorithm as well as SEO in general applies only to organic search and not at all to paid search.
Each search engine has its own process for building a search index and is maintaining it independently. As of 2025 Google’s market share in this space is 93% in the UK and 87% in the US.
Why is it Important to Know How Search Engines Work?
- Understanding the basics of how search engines work is imperative for Onpage SEO. It ultimately helps with the answers to the most rudimentary questions as to why certain pages rank and others do not. The more thorough your understanding of the elements and processes behind search engines becomes, the more equipped you are to understand the full picture of what it will take to rank for your target keyword.
- Understanding some basic aspects of how search engines work with particular reference to how they interpret hyperlinks between websites to estimate authority, relevance, trust of any website on the web will also serve as a foundation for understanding Link-Building and its importance for further amplifying your Onpage SEO efforts.
- A beyond-basic understanding of how search engines work will also enable you to delve into the pivotal technical SEO factors that directly feed into how effective your Onpage Optimisation efforts will be at achieving your business objectives. It is through technical SEO that you will be able to further refine how much of an impact your Content Strategy and its overlayed Onpage Optimisation will have.
Deconstructing the Search Engine Process
At its core, the behind-the-scenes process that allows Search Engines to return a collection of website links in response to user search queries includes 4 steps, starting with data-collection in the form of Crawling and Rendering, then storing in the form of Indexing and finally, organisation in the form of Ranking, as described below:
- Crawling: The data-collection process of search engines through the use of bots (i.e. Googlebot) to discover new and updated content on the web.
- Rendering: The process search engines employ to execute a webpage’s code and generate the visual, interactive version of a web page that a human user would see.
- Indexing: The process of storing internal notes on the previously Crawled and Rendered web pages in a proprietary database, so that the web pages in question can be retrieved promptly in response to user search queries relating to the page’s content.
- Ranking: The process employed to determine the order of search engione results in response to user search queries, governed entirely by the Search Engine’s proprietary algorythm.
1. Search Engines Bots Discover Information by Crawling Website Pages
Frankly, to actuate technical SEO to your benefit on any given website you will need a thorough understanding of how search engines work beginning with the information discovery process of the search engine bots, often referred to as Crawling. The discovery process begins with a known list of URLs. Search engines can discover these in several ways:
From backlinks: Google has an index of over 400 billion webpages. When someone links to a new page from a known page, search engines can find it through the hyperlinks on these pages.
From sitemaps: Sitemaps tell search engines which web pages and files website owners want to be both crawled and indexed. This is another method that enables search engines to discover URLs.
From URL submissions: Search Engines allow site owners to request crawling of individual URLs from within their proprietary tools (i.e., Google Search Console for Google Search).
The role of robots.txt & robots meta tags: While sitemaps instruct robots on what pages are flagged for indexing, the role of the robots.txt file and robots meta tags is exactly the opposite. Both are employed to restrict robots from crawling or indexing certain pages, but it is also the place that specifies the URL of your XML sitemap.
If a crawler or search engine bot cannot access or efficiently navigate your website, your pages simply won’t be discovered and subsequently won’t appear in search results, regardless of their quality. Optimizing your site’s crawlability through proper site structure, internal linking, sitemaps, and managing crawl budget is crucial for ensuring search engines effectively discover all your valuable pages and content within it.
2. Search Engines use Rendering to interpret pages the way Website Users are intended to
Rendering is when search engines attempt to run a page’s code in order to extract key information from the crawled pages and perceive it as a user would. Understanding Rendering will enable you to ensure all the content that is part of any given page makes it into the search engine index in a predictable way and not only a part of it. Without this understanding parts of your onpage content might remain invisible to the systems meant to find it.
Learning how to ensure all your page content is accessible to search engine bots and fully rendered by them is primarily important because if only a part of the page content is accessed, it puts you at a disadvantage as the unrendered content, potentially including important keywords and internal links, won’t be considered when establishing your Page Ranking for various keywords.
Once crawled and rendered any given page is ready for Indexing, but an important sidenote on Rendering would be that even if any given page has been indexed – it does not by extension imply that all of its content made it into the index. So you might remain unaware that not all the page content is employed in building up your website or page rankings. This is, of course, unless you understand and test the rendering of the page.
3. Indexing defines what ends up in Search Engine databases
Indexing is the process of adding information from crawled pages to a search index. The search index is what one searches when using a search engine. That’s why getting indexed in major search engines such as Google is so important for businesses. Users can’t find your businesses unless they’re in the index.
Crawling and Rendering together with the indexing rules specified on any given page will enable either the inclusion or exclusion of a page from the search engine index. If your pages are not successfully indexed, they will not get the chance to rank in search results, even if crawled and rendered perfectly.
At its core, it’s important to understand indexing in order to be able to make the distinction between an indexable and non-indexable website page, one that has been indeed indexed and one that hasn’t and if a page is indexable but not indexed – understand the root causes that prevents the indexing of the page by any given search engine.
4. Ranking is Search Engine Algorithm’s matching of Search Queries to a prioritised list of website pages from the Search Engine Index
Google also needs a way to shortlist and prioritize the 400 billion landing pages for all keywords from billions of its users worldwide to a more manageable number. This is where search engine algorithms come into play. Their sole purpose is providing the user a list of search results in the order it estimates to be most likely to solve the user’s search query.
Search engine algorithms are formulas that match the user’s keyword to relevant landing pages stored in the index in the form of search results. The search results are prioritized according to said search engine algorithm, with the result at the top being considered the single most relevant and useful for any one keyword in question.
No person knows every search engine ranking factor, not only because they vary across search engines but also because the search engines do not publicly disclose them. Nonetheless, search engines, including Google, have, in fact, disclosed to the public some of the key ranking factors as well as some best practices for SEO, which can prove quite useful to those with or without an SEO background.
Some of the key ranking factors are backlinks, content relevance and freshness, page loading speeds, and mobile-friendliness. It’s worth noting that users may see different results for the same keyword depending on their location, the language set on their browsers, and their search history.
Understanding the nuances of how search engines, primarily Google, rank pages for keywords and use them in its AI overview is what allows you to increase the visibility in organic search and by extension drive organic traffic through SEO. Understanding the multitude of factors that influence how a search engine orders results and the intricacies of each factor in isolation as well as in relation to other factors enables you to make informed judgment calls on various aspects of the website as a whole as well as individual landing pages in order to uplift them for target search queries and user intents in the SERPs.
Ultimately, the understanding of the search engine ranking factors, each contributing to the ordering of search results by the search engines is what allows the Search Engine Optimisation to take place. Mastering the principles of ranking allows you to position your content favorably against competitors and effectively connect with your target audience.