How Do Search Engines Work?

Nov 6, 20239 min read

Updated: Dec 4, 2023

Searching on the internet has become a daily activity for most of us. We think nothing of opening our favorite search engine, typing in a query, and finding relevant websites and information in seconds. But have you ever wondered exactly how search engines like Google and Bing are able to scour the vast expanse of the internet and return such targeted results?

In this article, we’ll unpack the three core functions of a search engine.

Crawling - Searches the Internet for content, looking over the code and content for each URL they find.
Indexing - Stores and organizes the content found during the crawling process. Once a page is in the index, it gets sent to be displayed as a result to relevant queries.
Ranking - Provides the pieces of content that will best answer a searcher's query. Results are ordered by most relevant to least relevant.

Crawling: Discovering Web Pages

The first step for any search engine is to discover the billions of pages that exist on the web. This is done by crawl programs, also known as spiders or bots, that browse the web continuously. These automated crawlers start with a list of known web pages, identify any links on those pages and recursively follow the trail of links to traverse the web.

As they crawl, the bots extract and store information about each page, including page content, metadata, images, videos, links and more. Crawlers can crawl billions of pages per day to ensure search engines have a regularly updated catalog of the web.

Are your site pages being found?

It’s possible to block search engine crawlers from part or all of your site, or to instruct search engines to avoid storing certain pages in their index. There might be reasons for doing this, but if you want your content found by searchers, you have to make sure it’s accessible to crawlers and is indexable. Otherwise it’s just invisible.

Ensuring your website is crawled and indexed is essential for appearing in search engine results, and you can check the number of pages in the index by using the "site:yourdomain.com" search operator on Google, which will provide insights into how effectively Google is crawling your desired pages.

For more precise results, utilize Google Search Console's Index Coverage report. This will allow you to submit sitemaps and track the inclusion of pages in Google's index. If your site is not appearing in search results, possible reasons for that include:

Being new
Lacking external links
Having a difficult-to-crawl navigation
Implementing crawler directives that block search engines
Being penalized by Google for keyword stuffing

If you found that some of your pages are missing from the index there are some optimizations you can implement to better direct Googlebot on how you want your web content crawled. Telling search engines how to crawl your site can give you better control of what ends up in the index. To direct Googlebot away from certain pages and sections of your site, use robots.txt.

Robot.txt

Robots.txt is a text file placed in the root directory of a website that provides instructions to web crawlers, such as search engine bots, on which pages or parts of a website should or should not be crawled or indexed. It's a tool used by website owners to control the access of web crawlers to their site's content and helps manage the visibility of specific web pages in search engine results. By specifying which areas of a site should be off-limits to search engines, website administrators can protect sensitive information and optimize their site's crawl efficiency.

Although it might seem logical to block crawlers from private pages such as login and administration so that they aren't in the index, placing those in a publicly accessible robots.txt file also means that people with malicious intent can more easily find them. It’s best to NoIndex those pages and put them behind a login form rather than place them in your robots.txt file.

Make Sure Crawlers Find All Your Important Content

A bot needs to be able to crawl through your website and not just to it.

Login Form

Requiring users to log in and fill out forms before accessing certain content means search engines won't see those protected pages.

Search Form

As with login forms, website crawlers can't use search features on your site. So if your site relies heavily on a search box you might have crawl issues.

Site navigation is crucial when crawling a website as it plays a central role in helping search engine crawlers efficiently access and index web content. A clear and well-structured site navigation system ensures that search engine crawlers can easily navigate through your website. Additionally, it helps determine the relative importance of pages by signaling which content should be prioritized for indexing, potentially boosting their visibility in search results.

Unclear or Hidden Navigation: If your site's navigation is unclear, hidden behind JavaScript or other dynamic elements, or primarily relies on images without alternative text, crawlers may struggle to follow links and access your content. Use clear, text-based navigation and avoid excessive reliance on JavaScript or images for critical links.
Orphaned Pages: Orphaned pages are those that lack internal links to them. If certain pages on your site are not linked to from other pages or the main navigation, crawlers may have difficulty discovering and indexing them. It's essential to include internal links to all important pages.
Complex URL Structures: Complex URL structures with multiple parameters or dynamically generated URLs can confuse crawlers. A clean and consistent URL structure is preferable, making it easier for crawlers to understand and index your pages.
Excessive Reliance on AJAX or Flash: Using AJAX or Flash for navigation elements can create issues for crawlers because these technologies often hide content from traditional crawling methods. Providing alternative HTML-based navigation and content is important for accessibility and indexation.
Broken Links and Redirect Loops: Broken links or redirect loops within your site's navigation can disrupt the crawling process. Crawlers may struggle to follow these links and may miss out on content. Regularly check for broken links and ensure that redirects are correctly configured.

If your site doesn't have any other sites linking to it, you still might be able to get it indexed by submitting your XML sitemap in Google Search Console.

Crawl Errors

In the process of crawling the URLs on your site, a crawler may encounter errors. You can go to Google Search Console’s “Crawl Errors” report to detect URLs on which this might be happening

4xx Codes

4xx status codes are client error responses in HTTP, indicating that the request sent by the client (usually a web browser) is problematic or incorrect. These codes are typically caused by issues on the client's side, such as requesting a non-existent page (404 Not Found), unauthorized access (401 Unauthorized), or a forbidden resource (403 Forbidden). They signify that the client needs to rectify the request to access the desired content.

5xx Codes

5xx status codes are server error responses in HTTP, signifying that the server has encountered an issue or failure while attempting to fulfill a valid client request. These codes indicate that the problem lies on the server's side and not with the client. Common 5xx codes include 500 Internal Server Error, which suggests a generic server problem, and 502 Bad Gateway, indicating a server acting as a gateway received an invalid response from an upstream server.

Thankfully, there is a way to tell both searchers and search engines that your page has moved by using the 301 (permanent) redirect.

Once you’ve ensured your site is optimized for crawlability, the next order of business is to make sure it can be indexed.

Indexing: Organizing the Web

As crawlers discover web pages, the content and data from each page is stored and organized in a massive index. This search index is like a giant database of web pages that allows for efficient look-ups and matches.

When indexing pages, search engines analyze page content and associate pages with relevant keywords or concepts. This enables fast matching between search queries and related pages when users perform searches. The search index is constantly evolving as crawlers revisit sites and update the index with new content and links.

Are Your Pages Missing?

You can use the URL Inspection tool to learn the status of the page you think might not be indexed. If you do find that one or multiple of your pages aren't indexed you can request indexing within GSC to submit individual URLs to the index.

Tell Search Engines How to Index Your Site

To convey specific indexing instructions to search engines, webmasters can utilize robots meta directives, robots meta tags, and the X-Robots-Tag HTTP header.

Robots Meta Directives

Robots meta directives are HTML elements placed in the head section of a web page and specify whether search engines should crawl or index the page. The "noindex" directive, for instance, tells search engines not to index the page, while "index" indicates the opposite. Similarly, the "nofollow" directive tells search engines not to follow the links on the page, which can be useful for preventing the indexing of unimportant or duplicate content.

Robots Meta Tags

Robots meta tags are another way to convey these directives and are placed in the HTML code of individual pages. They can be useful for fine-tuning indexing instructions on a per-page basis.

X-Robots-Tag

In addition to HTML-based methods, webmasters can use the X-Robots-Tag HTTP header to communicate directives for indexing to search engines. This header is sent from the web server to the search engine crawler and can be used to instruct crawlers not only at the page level but also at the server level, influencing how all pages on the site are treated. For instance, we can use this header to specify that certain types of files or sections of the website should not be indexed. Utilizing these methods, we have a range of tools at their disposal to precisely control how search engines crawl and index their site, ensuring that only the most valuable and relevant content is included in search engine results.

Ranking: Determining Relevancy

The indexing process ensures search engines can quickly find web pages for any search query. But determining the most useful and relevant pages requires a ranking system. When you search for something, the matching pages are ranked based on key elements like:

Keywords - Pages containing your exact search terms will rank higher.
Content - The relevance of page content to the query.
Popularity & Backlinks - Popular pages and pages linked to by other sites rank better.
User experience - Metrics like click-through rates, dwell time.
Freshness - Newer pages may rank higher for breaking queries.

Search engines use complex, secret ranking algorithms that assign a score representing overall relevancy. Pages with the highest scores appear first in search results. The ranking algorithm is continually tweaked based on user searches and interactions to improve search quality.

How SEO Relates In All This

Websites that secure higher positions in search engine results pages enjoy greater visibility to users actively seeking information or services. This heightened visibility translates into increased click-through rates, boosting the site's organic traffic, user engagement and SEO. Additionally, high-ranking websites are often deemed more credible and trustworthy by users, an essential factor in building user trust and facilitating conversions. The criteria used by search engine algorithms to determine rankings are multifaceted, encompassing elements like content quality, relevance, user experience, site speed, and mobile-friendliness.

Achieving top positions in SERPs offers a competitive edge in the online marketplace, positioning a website as a leader in its niche. This elevates brand exposure and market share.

Localized Search

Localized search is a search engine process that provides users with results specifically tailored to their geographical location or search intent. It's a fundamental aspect of search engine technology, particularly for queries related to local businesses, services, or events. Localized search relies on three primary factors: relevance, distance, and prominence.

Relevance

Relevance refers to how well a particular listing or webpage matches a user's search query. In localized search, the results must closely align with the user's location and intent. For example, if someone searches for "coffee shops," a relevant result would be a nearby coffee shop that matches the user's preferences. Search engines analyze various signals to determine relevance, including the presence of location-specific keywords, the content on webpages, and user reviews.

Distance

Distance signifies the proximity of a business or location to the user conducting the search. Search engines use the user's current location, or a location they specify, to calculate how far a given result is from them. Results that are geographically closer to the user are more likely to be prioritized. This factor ensures that users receive relevant results that are conveniently accessible.

Prominence

Prominence takes into account the reputation and credibility of a business or location. Factors such as the number and quality of reviews, the quantity and quality of backlinks to the website, and the overall online presence contribute to prominence. A well-known, highly-rated business is more likely to be considered prominent and, therefore, ranked higher in localized search results.

Why is Google So Popular?

Not all search engines are equal when it comes to SEO. The truth is that despite the existence of more than 30 major web search engines, the SEO focus is mostly on Google. But why? Simply put, Google is where the vast majority of people search the web. More than 90% of web searches happen on Google, nearly 20 times Bing and Yahoo combined. With Google's dominance over the search market, it's important to focus your time and SEO there.

Closing Thoughts