Understanding How Search Engines Work: Crawling And Indexing Pages

Summit Ghimire January 5, 2023 - 16 minutes to read
Understanding How Search Engines Work: Crawling And Indexing Pages

When it comes to SEO, there is a lot of talk about “crawling” and “indexing pages.” But what does that mean? 

Here’s a simple explanation, crawling is the process by which search engines discover new content on the web. Indexing, on the other hand, is the process of adding new content to the search engine’s database. In other words, crawling is like going on a treasure hunt, while indexing is like adding treasure to your hoard. 

This blog post will take a more in-depth look at how search engines crawling and indexing pages works. By understanding how this process works, you can optimize your website for crawlers and improve your chances of ranking high in search results.

An elementary understanding of Search Engine

Search engines are programs that search the internet for websites that match the keywords entered into the search bar. Search engines work by indexing, or cataloging, all of the websites on the internet. When a user enters a keyword into the search bar, the search engine uses its index to find websites that contain that keyword. Search engines are essential for finding information on the internet. Without them, users would have to manually browse through every website to find what they were looking for. 

Did you know?

  • The most popular search engine, Google, handles over 3.5 billion daily searches.

Except for google, other popular search engines include Bing and Yahoo. Search engines are constantly evolving, with new features frequently added. For example, Google now has results from news articles and maps in its search results. As the internet continues to grow, so do the capabilities of search engines.

Main parts of Search Engine: Web crawler, Search Index, & Search Algorithm(s)

Search engines are one of the most commonly used tools on the internet, but how do they work? 

The main parts of a search engine are the web crawler, search index, and search algorithm

  • The web crawler explores new and updated websites and adds them to the search index. 
  • The search index is a database of all websites and pages the web crawler finds.
  •  The search algorithm then uses this index to match websites with user queries, considering factors like relevancy and popularity.

Extensively explaining, search engines maintain a database known as a search index containing billions of documents across the web. The search engine uses a complex algorithm to scour its index and return relevant results when you perform a search. 

The search algorithm considers factors like:

  • The location of the document’s search terms.
  • How many other websites link to that document? 

At their core, search engines rely on these three main components.

How does Search Engine Ranking work?

Search engine ranking is how search engines like Google order search results. It’s a complicated process. Google considers more than 200 factors to determine which websites to show on the first page of search results and which to deliver on later pages.  

Some of the factors that search engines look at when ranking websites include:

  • The quality and quantity of the site’s content, 
  • The number of other websites linking to it, and 
  • The speed and usability of the site. 

Search engine ranking is an important factor in determining how much traffic a website receives, and it can have a big impact on a business’s bottom line. That’s why many companies invest heavily in search engine optimization, or SEO, improving a website’s search engine ranking.  

Introduction to the functions of Search engines


The URL, or Uniform Resource Locator, is the starting point for all search engine queries. The URL is the first thing the search engine checks when you enter a question into a search engine. If the URL matches the query, the search engine will return results from that website. If not, the search engine will search other websites until it finds a match. The URL is thus essential for finding the right results in a search engine query. 

How does Google discover URLs?

Google uses a variety of methods to discover URLs. 

One common method:

When Google crawls the web, it follows links from one site to another.  As it does so, it discovers new URLs that it can add to its index. 

Google can also discover URLs:

  • By crawling XML sitemaps that website owners submit. 

These sitemaps help Google find pages that might not be easily discoverable through traditional link crawling. 

Note: Google also offers a URL submission tool that allows website owners to manually submit their URLs for inclusion in the search index. 

URL submission tool is often used for new websites or for pages that have been recently updated and still need to get indexed through other methods. 

By combining these different methods, Google can keep its search index up-to-date with all the latest URL discoveries.

B. Crawling

It all starts with spiders

When you enter a search query into a search engine, it scours its index of websites to find the best possible matches for your question. The search engine uses special software called web crawlers, or spiders, to crawl and index web pages.

Spiders start at a list of known good pages (typically provided by the search engine operator) and then visit each page. As they visit each page, they read the content and follow any links. They then add those new pages to their list of available pages, and the cycle continues. The more pages a spider crawls, the larger the search engine’s index. And the larger the search engine’s index, the more accurate its results will be when you search.

For example,

Google uses a crawler called Googlebot to crawl the web and index pages. When Googlebot visits a site, it reads the page’s HTML code to identify links on the page. It then follows those links to discover new pages. Once it has uncovered new pages, it adds them to its list of pages to crawl in the future. In this way, crawling is essential for search engines like Google to keep their results up-to-date.

Types of crawling

  1. Depth-first crawling
  2. Breadth-first crawling

Depth-first crawling explores a website by starting at the home page and then going down through the links to find new pages. This crawling finds new content quickly.

On the other hand, Breadth-first crawling starts at the home page and then goes out to explore all of the links before moving on to the next page. This type of crawling is often used for websites with many pages, ensuring that all pages get crawled eventually. 

There are also hybrid methods that combine both depth-first and breadth-first approaches. Ultimately, the best method depends on the specific website and what type of information is being sought.

Can crawlers find all the content?

  • Crawlers are the unsung heroes of the internet- they help search engines index content so that we can find the information we need. 

But can crawlers find everything? 

  • The answer is yes and no. 

Crawlers are very good at finding static content that is updated frequently. This static content includes things like the following:

  • Product pages, 
  • Blog posts, and 
  • Articles 

However, they need help finding dynamic content, such as user-generated content or comments. This difficulty happens because this dynamic content is often created or updated in real-time, making it harder for crawlers to keep up. As a result, search engines do not index some ranges. 

Additionally, crawlers can sometimes have difficulty accessing certain types of content, such as Flash or JavaScript. So, website owners need to take measures to ensure that crawlers can easily find and index their content. 

Note: Self-indexing can involve using Crawler Instructions, which guide how to find and index specific types of content. 

These steps help website owners ensure that their site’s content is properly indexed and crawled.

The crawling errors when accessing URLs

When you try to access a URL and receive an error, it’s often due to the following:

  • 4xx Codes
  • 5xx Codes

4xx codes are client-side errors, which means there’s something wrong with the request you’re sending.

Common 4xx codes include:

  •  404 (not found) and 
  • 400 (bad request). 

5xx codes are server-side errors, which means the problem is on the website’s end.

Common 5xx codes include:

  • 500 (internal server error) and 
  • 502 (bad gateway)

While 4xx and 5xx errors can be frustrating, there are ways to troubleshoot and fix them. 

Note: 4xx errors are usually due to incorrect URLs or syntax issues, while 5xx errors happen due to overloaded servers or database issues.

If you encounter a 4xx or 5xx error when trying to access a URL, 

  • Check the address for typos, and make sure you’re using the correct syntax. 
  • If that doesn’t work, contact the website’s owner or administrator to report the issue. They should help you resolve the error so you can access the content you’re trying to reach.

C. Indexing

Indexing is a crucial process for optimizing the performance of databases. By indexing data, DBMSs can more quickly locate and retrieve specific records. There are several different indexes, each with its strengths and weaknesses. 

The most common index type is:

  • B-tree index (which organizes data in a hierarchical tree structure)

The B-tree index efficiently retrieves records based on their key values. 

Another popular index type is:

  • The hash index (which uses a hashing algorithm to map key values to specific records)

Hash indexes are particularly well suited for performing equality comparisons. 

Finally, there is:

  • The bitmap index (encodes data as an array of bits)

Bitmap indexes are very space efficient and can efficiently answer range queries. You can create indexes on almost any data type, including numerical data, text data, and images. Indexes can be made on one or more columns in a table and can even be created on expressions that combine multiple columns. 

Database administrators can create indexes manually, or the DBMS can automatically generate them. You must carefully choose indexes to strike the right balance between performance and space usage. Too many indexes can result in excessive disk usage, while creating too few indexes can degrade performance. Indexes are a powerful tool for optimizing database performance, but you must use them judiciously to achieve the best results.

Search engine interpretation and restoration of pages

Indexing is the process that search engines use to interpret and store your pages. 

  • To do this, they first need to understand what your pages are about. This is done by looking at the content on your pages and any metadata you may have included.
  • Once they understand your pages well, they can start indexing them.
  • Indexing involves storing your pages in a database to easily retrieve them when someone searches for a relevant term. However, indexing can also store other information, such as the popularity of your pages or the number of inbound links. This information can help determine how to rank your pages in the search results.

As you can see, indexing is a vital part of how search engines work, and it is important to ensure that your pages are properly indexed to ensure that they are visible in the search results.

However, sometimes these algorithms can misinterpret a page, or a website can change and no longer be about the same topic. In these cases, it’s important to submit a request to the search engine to have the page re-indexed so that it can be accurately represented in search results. This process is called “restoration.” 

By restoring pages that have not properly been indexed or are no longer relevant, search engines can provide more accurate and helpful results to users. As a result, restoration is essential to maintaining a healthy website.

How to tell search engines to index your site faster?

1.  Check Your Site’s Indexing Status

Before you can tell search engines to index your site, you must check its current indexing status. You can do this using a tool like Google Search Console. Enter your website’s URL into the tool, and Google will show you which pages are currently indexed.

2.  Submit a Sitemap

If you want search engines to index all of the pages on your site, you need to submit a sitemap. A sitemap is a file that contains a list of all the URLs on your website. This sitemap makes it easy for search engines to find and index your content.

3.  Use robots.txt

Another way to tell search engines which pages on your site to index are by using the robots.txt file. This file contains instructions for how search engine bots should crawl and index your website.

4.  Add Structured Data Markup

Structured data markup is code added to your website’s HTML code that helps search engines understand the meaning of your content. This data can tell search engines what type of content is on each page, such as articles, products, or events. Adding structured data markup to your website can improve search engines’ chances of indexing it.

5.  Promote Your Content

Once you’ve ensured that search engines properly index your website, you need to promote your content so people will see it in the search results. The best way to do this is by creating high-quality content that people are likely to search for. You can also promote your content through social media and other online channels.

How to index your content faster?

1. Use sitemaps

A sitemap is an XML file that contains a list of all the URLs on your website. By submitting a sitemap to the major search engines (Google, Bing, etc.), you’re giving them a road map of your site so they can easily find and index all your content. There are two types of sitemaps: XML and HTML sitemaps. XML sitemaps are meant for search engines, while HTML sitemaps are for human visitors to your site. Generally speaking, you should submit both sitemaps to the major search engines. That way, they can find and index all your content as quickly as possible.

2. Optimize your robots.txt file

Your robots.txt file is a text file that contains instructions for the search engine bots that visit your site. You can use it to tell the bots which areas of your site you do or don’t want them to crawl and index. 

For example, if you have pages on your site that are still under construction and not ready for public consumption, you would add those URLs to your robots.txt file so the bots wouldn’t try to index them (and they would eventually get an error message). 

You can also use wildcard characters in your robots.txt file, so you don’t have to list out each URL you want to block individually; block all URLs that match a certain pattern. 

3. Submit individual URLs directly to the search engines 

If you have new content on your site that you want to be indexed right away, one of the best things you can do is submit those URLs directly to the major search engines using their respective webmaster tools platforms: Google Search Console and Bing Webmaster Tools. Once you submit a URL, you will add it to the queue of pages waiting to get crawled and indexed; generally speaking, it will be picked up and indexed within a day or two (sometimes even faster). 

4. Diversity is Key

One common mistake people make when trying to improve their SERP ranking is keyword stuffing—adding too many keywords into their content to game the system. However, this is unnecessary and will hurt your chances of being ranked well by the search engines because it creates a bad user experience (UX). Instead of stuffing keywords into every nook and cranny of your site, focus on ensuring each page has high-quality, keyword-rich content relevant to what people are searching for. In other words, focus on quality over quantity—the opposite of what most people think they need to do! 

Focus on making sure each page has high-quality, keyword-rich content that’s relevant.

5. Include images & videos 

In addition to text-based content, another great way to improve your SERP ranking is by including images and videos on your website wherever possible—especially if those images and videos get optimized with keywords! Not only will this help improve your ranking, but it will also help keep visitors engaged with your site longer (which is always a good thing). 

Indexing vs. Rendering

The two important steps in search engine optimization (SEO) are: 

Indexing: Adding web pages to a search engine’s database. This addition enables the pages to be found and displayed in search results. 

Rendering: The process of generating HTML code for a web page. This code displays the page in a web browser. 

Indexing is generally performed by bots or crawlers, while browsers perform rendering. Both processes are important for SEO, as they determine what content a search engine can find and how it will get displayed in search results to users. Google indexes first, followed by rendering, allowing the search engine to show users the most up-to-date web page version. 

How do searchers interact with your site from search results?

When someone enters a query into a search engine, it scours its indexed pages to find the most relevant results. A complex algorithm determines the order in which these results get displayed. The search engine considers dozens of factors, such as: 

  • The quality of the content, 
  • The popularity of the site, and 
  • The user’s previous search history. 

However, even the most well-optimized site will not get many clicks if its listing isn’t eye-catching and informative. This is why it’s important to understand how searchers interact with your site from the search results page.

Types of searchers

There are different types of searchers, each using another method to find the information they are looking for.

Searcher #1: Navigational

One type of searcher is the navigational searcher. These users already have a specific website in mind that they want to visit. They use the search engine to find the correct URL. For example, if you wanted to visit Amazon, you might type “amazon.com” into the search bar.

Searcher #2: Informational

Another type of searcher is the informational searcher. These users are looking for specific information but need to have a particular website in mind. They use the search engine to find the best source of information for their needs. For example, if you wanted to learn about the history of pandas, you might type “panda history” into the search bar.

Searcher #3: Transactional

The last type of searcher is the transactional searcher. These users are looking to buy something online. They use the search engine to find websites where they can purchase. For example, if you want to buy a new pair of shoes, you might type “shoes” in the search bar.

Types of Queries

a. Keyword query

The most common search engine query type is a keyword query, which consists of one or more keywords that the user enters into the search engine.

b. Boolean query

Search engines rely on algorithms that match the keywords to relevant websites to interpret keyword queries. Another type of query is a Boolean query, which uses operators such as “AND” and “OR” to combine multiple keywords. Experienced users search these queries to narrow their search results. 

c. Natural language query

Finally, some users may enter a natural language query, a sentence or phrase describing what the user is looking for. Natural language queries are typically processed using artificial intelligence techniques. 

By understanding how different types of searchers interact with search engines, businesses can design their websites and content in a way that is more likely to be found by potential customers.

Relationship of queries and SERP Features

Search Engine Results Pages (SERP) feature snippets directly result from users’ search queries. The snippets are generated algorithmically by matching the user’s query with the content on web pages. 

The relationship between queries and SERP features is important for anyone who wants to optimize their website for search engine ranking. 

Note: When a user enters a query, the search engine looks at the SERP features to determine what information to return. 

The SERP features have two categories: 

  • Organic 
  • Paid

Organic SERP features are unpaid results displayed based on relevance to the user’s query. 

Paid SERP features are the results that are displayed because the website has paid for them to Google to show. The goal of SEO is to rank high in the organic results, as this will result in more traffic to the website. 

Did you know?
  • Google uses an artificial intelligence system that ranks 
    websites based on user engagement called RankBrain.

Several factors determine how well a website will rank for a particular query. Still, one of the most important is the relationship between the question and the SERP features. If a website can optimize its content and structure to align with the SERP features, it will likely see an increase in its search engine ranking.

This way, a searcher types the query and gets its required information through search engines.

[Bonus] How does Google adjust SERP order in response to searcher engagement?

Google is constantly tinkering with its search algorithms to provide the best possible user experience. 

  • A major factor in determining the order of results on a given search engine results page (SERP) is engagement

One of the most important factors that Google takes into account when ordering results is the–

  • Clicked-through rate (CTR). 

CTR measures how often searchers click on a particular result when it appears on the SERP. It stands to reason that Google would prefer those results that get clicks more often, as they are more relevant and useful to searchers. 

In addition to CTR, Google also looks at other engagement metrics, such as–

  • Dwell time 
  • Pogo-sticking

Dwell time is what a searcher spends on a particular website after clicking through from the SERP. 

Pogo-sticking refers to clicking back to the SERP after quickly realizing that the clicked-through result is irrelevant. Again, it makes sense that Google would prefer those results that keep searchers engaged once they click through. 

By taking into account a variety of engagement metrics, Google can deliver more relevant and useful results to its users.

However, engagement happens due to several factors, such as:

  • The relevance of the result to the user’s query
  • The title and description of the result
  • The overall reputation of the website. 

Google considers all of these factors when determining SERP order, and it is constantly tweaking its algorithms to provide the most relevant and engaging results for users. 

As a result, businesses that want to ensure their website appears prominently on SERPs must focus on creating relevant and engaging content for users.

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