Search engines are your portal to the internet. They break down huge mountains of information to answer a user's query in milliseconds. They make it seem simple, so how do search engines actually work?

To discover, categorize, and rank the billions of websites that make up the internet, search engines use sophisticated algorithms with a goal to answer search intent. They have already qualified the pages in their database, so they can answer those queries with matching URLs at lightning speed.

It's a complex process that's broken into this basic summary:

  • Search engines send out bots to read web pages,
  • They store what they find in a massive database, and
  • They answer searches using the data they stored about each page.

All of that data includes ranking factors, or qualities, about the page itself. Those details help search engines determine which pages are most likely to give the user what they're hoping to find.

Understanding the behind-the-scenes processes that make search engines work can help in your SEO work. When you are mindful about why certain pages rank well, you can craft strong content with the potential to rank higher.

How Do Search Engines work?

To be effective, search engines need to understand exactly what kind of information is available and present it to users logically. The way they accomplish this is through three fundamental actions: crawling, indexing, and ranking.

Search engine process flow

Through these actions, they discover newly published content, store the information on their servers, and organize it for your consumption.  Here's a look at what happens during each of these actions.

Crawling: How search engines find your pages

What does crawling mean to search engines?

Crawling is the way that search engines find your pages. They send out their own web crawlers, but you might be more familiar with the terms bots and spiders. I love the imagery that these are straight out of a Spider-Man movie, but sending out crawlers is less "spider-army" and more "massive wall of dedicated computers."

These crawlers "read" your web page to review the content, especially new pages and existing content that has recently been changed. Crawling is the process of identifying URLs, sitemaps, text and code to understand the type of content being displayed and learning where to crawl next.

Internal links play a big role in guiding the bots to other pages on your site. Those links support sitemaps in helping crawlers discover the pages on your site and the context to what they are about. That's why a good internal linking practice is such an important part of growing your SEO footprint.

Tell search engines how to crawl your site

Depending on the stage from crawling to ranking, the amount of control that you have over search engines ranges from "give it directions" to "just hope for the best." In this stage, you have a say in how your site is crawled. Search engines use their own algorithms to determine how to crawl your pages, but you set additional permissions through your Robots.txt file. Since crawling is just a matter of bots discovering your pages--one after another--this is more like allowing guests to tour your house, but some doors are closed.

Robots.txt

Robots.txt file is the set of rules about which pages are allowed to be crawled and which should be ignored. It's a simple text file that lives at the root of your site. (www.domain.com/robots.txt) It establishes a user agent and the files that specific bot has access to (or not). The user agent can be specific, like "googlebot" or use an asterisk "*" as a wildcard, applying to all bots that crawl your site.

Google Search Central explains that the purpose of robots.txt is to keep their bots from overloading your site with requests. Blocking Google entirely from a page is best handled through "noindex." Look for more information on that in the Index section further ahead.

Sitemaps

A sitemap helps crawlers learn where pages are located on your site, how they are organized, and which ones should be crawled more often than others. It's a list of all of your site's URLs and helps search engines crawl your site efficiently and thoroughly.

A well-optimized sitemap also includes information on the format of the page (video, for example), how recently the page was updated, and other languages that the page can be shown in. You can also give priority to pages that are updated more often so that crawlers will visit those more often than pages that are static and less important.

By improving the visibility and context of your pages, sitemaps enhance a website's SEO performance.

Redirects

Redirect instructions tell the crawlers that a page has been moved to a new location.

Usually when you update a page, you change the text or add rich content and set it live. Pages evolve, and crawlers pick up the new version when they return. However, if you change the URL of that page or remove a page altogether, the original URL doesn't disappear from the internet. Using a redirect tells the crawler that it should recognize a new page in its place.

A permanent 301 redirect tells the crawler that the new destination page should be treated as the final, canonical version. A temporary redirect will instruct the bots to keep your original page in the results for a while, as you aren't removing it altogether. This is helpful when you are temporarily removing a service that you offer.

Issues with your crawl

If the bots run into any issues while attempting to crawl your pages, this can turn into bigger problems for your site's SEO. Pages that aren't crawled won't be indexed and displayed in search results, hurting your site's visibility.

Why search engine bots can't crawl your pages

Crawl issues tend to have basic culprits. Bots don't crawl pages that they can't access. For instance, pages that require a login generally won't be crawled. Other causes are 404 errors (page not found), which signal a page that has been moved or deleted without a proper redirect, and 500 errors (server issues), indicating a problem with the server hosting the website.

We also found that pages cannot be crawled because of simple errors in your robots.txt file, but there's an easy fix.

You can use tools like Screaming Frog to crawl your site and detect those issues. It also detects broken links which could also point to a crawl issue on your page.

Indexing: How search engines store your page details

What does indexing mean to search engines?

The index step stores important details that the crawlers discovered about each page. Search engines use software to organize pages based on their content so it can retrieve them later to answer a search. This extensive process adds web page details to a massive database.

Indexing saves the data about a page, including positive and negative ranking signals. It also reviews the page's tags and attributes, assessing whether this page is the right one to be stored in the index so it can be served in a search.

Tell search engines how to index your site

As a site owner you have more specific ways to tell search engines how to assess your pages. Consider this less "telling" and more "strongly suggesting." Instructions in the form of metadata and schema give search engines more context about the intention of your page.

Metadata and Structured Data

The term metadata covers many search engine directions in the indexing stage. A key standout is the robots meta tags.

By adding this tag in the HTML head of a webpage, site owners can instruct search engines not to index a page or follow the links on it. Common directives include noindex, nofollow, noarchive, and nosnippet. Notice that index and follow are not listed as they are the default instructions.

An alternate way to accomplish this is by setting the X-Robots-Tag in the HTTP header. You can also set user agents here, giving nofollow instructions to googlebot and setting different instructions like noindex to the other search engine bots.

Structured data gives the search engines directions for how to interpret the page data in a system called schema markup. It's visible only to search engines and can tell them to index and display your page as a recipe, or it makes your event page more accessible when searchers are looking for its date, location, or ticket prices.

Using schema markup does not guarantee that your instructions will be followed, but it's a good bet--and a good SEO practice. It can help search engines understand the content of a page better, leading to enhanced search results like rich snippets.

Canonicalization

When search engine bots discover pages that are very similar, the crawlers need instructions to tell them apart. You can help them understand that any multiple versions of a page that they discover are actually intentional.

Duplicate or near-duplicate pages exist for good reason. For instance, the www vs non-www versions of a page look identical, but they are two separate pages as far as search engines can tell. That's also the case with mobile pages compared to desktop versions or HTTP and HTTPS.

Your solution happens to be an SEO best practice. As the site owner, you can present an organized, clean site by establishing canonical versions--the page that you want search engines to serve--that erase any confusion.

You do this by adding rel="canonical" code in the <head> section of the web page.

Issues with Indexing

Even after a successful crawl, not all web pages get indexed. Several factors can play a part in that, especially technical issues and content quality. There's also a basic reason with an easy fix. We'll take a look at all of these.

Technical Issues

Technical problems can stem from how the website is structured or from problems in the code that throw off the bots. Some issues, like sitemap errors, cause crawl issues up front. Crawl issues lead to indexing issues. However, it's possible to have pages that are crawled but not indexed.

The error "crawled but not indexed" means that Google is aware of the pages, but something about the page itself didn't make the cut. If you rule out any of the expected reasons a page is not indexed (redirected, blocked by robots.txt, etc.) consider other possibilities:

  • Server or technical issues: The website had issues during the crawl or indexing process
  • Wrong canonical: The page has the wrong canonical tag attached

Should you find a page marked with that error, run it through the URL inspection in Google Search Console for an up-to-date status. It's possible that the issue has been resolved but not yet refreshed in the Page indexing report.  

Content Quality and Relevance

Search engines aim to serve up high-quality, relevant content. Pages that do not meet these standards may not get indexed. Some possible quality obstacles are:

  • Duplicate Content: Pages with content that is identical or very similar to other pages on the same site or across the web may be skipped over.
  • Thin Content: If the page has little substance or supporting details, it won't be deemed helpful to the user.
  • Low-Quality Content: Pages that contain spammy elements, excessive ads, or content that is not useful to users may be penalized.

Content Visibility and Access

Your pages need to be accessible to search engines. Further, the content should be "visible," not just to the human eye, but to the computers doing the indexing.

Let's say that you have pages that rely on resources like CSS, JavaScript, or images in order to make the page work. If any of those elements are blocked from being crawled, the page won't render completely. If the search engine can't render the page, it probably won't index it.  

That access extends to logins, too. Search engines can't reach pages that are kept behind logins, so those won't be indexed. That allows more sensitive information to be kept private--at least limited to those with permission to reach it.

Use Google Search Console for Indexing Issues

Using Google Search Console, site owners can control various ways of how their site is indexed, especially to troubleshoot any issues that arise. This includes requesting reindexing of specific pages and finding crawl and index errors.

Ranking: How search engines show pages in search results

Serving the results--and listing them in a particular order--is called ranking, but you might also hear that a search engine is returning or "surfacing" results. The data it finds during the crawl and index stages helps the search engine determine which results to show in a user's search.

What makes a page rank better than another one?

Search engines rank the results in order of relevance. The goal is to give the searcher the best possible answer to their query that they typed. Because that can be subjective, the search engines have to rely on multiple factors to improve the chances of getting it right.

Ranking Factors

Different search engines have their own mix of factors and weights to each factor that influence how search results are ranked. Even further, they might even display the page titles and descriptions differently.

However, certain key criteria stand out. You can confidently optimize your page for these key factors, improving your ranks on any SERP.

Relevance

The page needs to ultimately answer what the searcher wanted to find. Now, you're no mind-reader, but you can create content that covers a topic but then also touches on the subtopics and follow-up questions that go along with it. Specific details inside your page could be the exact match for a long question typed into a search bar.

It's better to go deep instead of wide.

Authority

As more of your web pages rank, search engines can detect your general expertise. Even smaller sites can establish that they are authoritative on a topic just as a more established site can. Better Homes and Gardens has excellent content on houseplants, but The Sill has stronger authority. As it is dedicated entirely to producing trustworthy content on plants around the home, it is likely to get new articles on houseplants to rank high and rank quickly.

You can mimic this practice by establishing content around your core services and then building pieces for closely related topics.

Quality

No searcher wants to click through to find that the article hardly answers their question or offers a good point of view. Quality content is well-written and thorough. Search engines give weight to pages that cover the topic with clear information and fleshed-out examples. And while there's little filler on the page, it doesn't necessarily have to be a long article. Some short pieces are considered high quality pages, mostly because they clearly answer the search without dragging the reader along.

Search Engines vs. Browsers

Search engines have gotten so sophisticated that they are now a seamless part of browsers. Most browsers have integrated search into their basic operation, making it easy for people to mistake one for the other.

Still, each one has a different role.

A web browser is software that allows users to interact with web pages on the internet. Examples of web browsers include Google Chrome, Mozilla Firefox, Microsoft Edge, and Safari. You can have more than one downloaded onto a laptop or a smartphone, but you usually set a default browser to open web pages from other sources--like a link in an email.

A search engine (Google, Yahoo!, and Bing), helps users find web pages that match their search.

A browser allows users to type in a URL or click on links to get to specific websites (or pages). A search engine allows users to type in keywords and phrases to search for specific information on the internet. A browser like Chrome will often have a search engine (Google) built in, making it seem to users like they are one and the same.

How do Search Engines Make Money?

Search engines generate revenue from a variety of services, but advertising is the dominant source. Each search engine has its own ad platform, with a few overlaps between affiliated companies.  

Search engine ads allow brands to promote their products and services on a search results page in exchange for a small commission each time a user clicks on the ad.

One form of advertising is online shopping. Brands can promote their products in a separate section of the search results, usually one that involves images and more details about the item.

Apart from ad services, search engines also expand into offerings like Google Apps and Firefox's sponsored new tabs.

Understanding How Search Engines Work Helps You Create Better Content

When you know how different platforms display their results, it is easier to create content with the potential to rank well. Optimizing your pages for relevant searches can help you drive more traffic to your website. It's the basic strategy of SEO.

SEO relies on major elements like technical on-page optimization, authoritativeness, and substantial, relevant content.

Technical optimization is a part of SEO that involves making improvements to the website's technical structure to make it more search engine-friendly. It includes user-focused signals such as improving website speed, fixing broken links, and optimizing for mobile devices.

Quality backlinks are links from other websites that point to your website. Search engines consider them as a vote of confidence for your website's content and authority. Having high-quality backlinks can improve your website's search engine rankings.

Finally, content is the core of what you are optimizing. Understanding how search engines work can help you diagnose why other types of content rank better or worse than your own.

We’ve put together five tips based on this information that can help you create better content across every platform:

  • Understanding user intent is important. Every platform we looked at today prioritizes content based on how relevant it is to a user’s search query.
  • Matching keywords will only get you so far. Including relevant keywords in your content will help search engines discover and index your content easier, but ranking well is more about providing value to users.
  • Know how your target customer searches. Matching both keywords and intent requires an in-depth understanding of your customers and how they think about your product and your market.
  • New content helps boost rankings. Creating new content or refreshing your existing content helps it rank higher and boosts your credibility as a brand.
  • Gaining authoritative links is helpful. The more people link to your page, the better it will appear to search engines. This signals that it’s valuable and relevant to the content of every page it links to.

In the end, it all comes down to understanding your customer. You can’t create content that ranks well if you don’t know what people are looking for when they search for your product.

For more information on creating content for search, check out our SEO Guide to learn more!