Web Crawling: What Is It, How Does It Work, & Why Should Care?

on SEO June 03rd, 2021

Not everyone is aware of web crawling or how it influences user behavior on the internet. 

Crawling is an essential process that helps us organize and access the immense amount of information found online. This is crucial for you if you want your business to be found in organic search results on Google and other platforms. 

Having the help of an expert is a great way to boost your results. But, make sure to research the different SEO companies and work with one that understands how crawlers impact search rankings. 

In this article, we’ll share our knowledge of crawling and how you can make sure that your website is easy for web crawlers to find and read. This includes the web crawler definition and how it differs from web scraping as well as everything you need to know about site indexation.

More Helpful Reading: https://www.fannit.com/seo/google-index/

What Is Web Crawling and What Are Web Crawlers?

But what is a web crawler? How exactly do this software help search engines organize and filter the entire internet? How do we define web crawlers?

First, a web crawler is a type of program that’s also called a web spider, crawler bot, or simply a bot. 

Crawlers are used by search engines to read and organize the contents of every single page of every single website on the internet. 

These programs essentially feed search platforms all the web information they need to create a giant database.

A web crawler is a type of software that acts on behalf of search engines and other types of platforms, so each platform has developed one or more unique web spiders. 

Just like they sound, these programs read every single part of your site line by line. Having a logical site structure and developing unique content for each page can help crawlers understand your site.

Every time it comes across a site, a web crawler starts to learn everything it can about the page’s data.

Crawlers work hard and try to do this for as many web pages as possible.

Once a web page is known to the crawler tool, the web crawling software indexes it along with the others, making sure the data is known and easy to find for a search engine.


web crawlers

The Web Crawlers-Search Engine Link

When you type a search term into Google or another free search engine tool, it will present you with a list of relevant links.

However, it would not have known this information and data wouldn’t be readily available if it was not for its web crawler trawling through the world wide web and sorting it into easy-to-find categories. 

Web crawling software allows search engines to get a user’s results as efficiently as possible.

You may have known about them under a different name.

Crawlers are often called spiders, robots, or bots, and it sums up nicely exactly what they do. 

These automatically crawl through the world wide web in a process that sorts sites out into different categories based on their available information and data. 

So the crawler can then gather information and send it back so that search engines index each site properly.

Have you ever color-coded your filing cabinet to make it simpler and faster to get relevant files? 

Or perhaps used the Dewey decimal system to help get a book at the library, amongst a huge number of shelves? 

A web crawler program is the digital search engine’s equivalent to physical data sorting systems.

How Do Web Crawlers Work?

Sifting through the reams of data and millions of pages on the internet is certainly no small feat.

On top of this, new websites are being designed and uploaded all the time. This means more new data is being created every day that isn’t yet known by any search engine.

There have been many new websites launched since you started reaching this blog! 

So, how does a crawler program manage to undertake the seemingly gargantuan task to get and download all this data?


First of all, they start with a list of already known and reliable sites and known URLs whose data they have already finished categorizing and indexing. 

This list is known as a ‘seed’.

The web crawler then looks for links on these pages and follows them through. 

Each link presents an opportunity for the crawler to index a new website, sort its data, and send it back to the search platform. 


The web crawler will then scan each page it visits, recording all the information and data.

It scans this data for a number of factors such as keywords. This gives the bot insight into which categories it should index each page under.

This is how Google ends up with a list of relevant sites whenever a user performs a search.

Bots then repeat the web crawling process, going from link to link, and recording information as well as data from each site. This regular crawling goes on around the clock. 

If you’ve ever used Wikipedia then you will probably be able to relate to what web crawling is. 

Of course, as anyone who’s ever used the internet knows, there are countless links on every website. So, the crawling process of each one could easily go on forever.

Categorizing and indexing the data for all the websites and each and every page on the internet would require a massive amount of time, even for the fastest web crawler. 

Work-wise this is possible, but it requires planning. 

Without proper guidance, web crawling could easily get bogged down amongst the millions and millions of web pages. 

Some of these might not have relevant or useful data, thus leading to poor results for search engine users.


Search engines use algorithms for web crawling, giving crawlers a specific set of instructions and conditions for choosing which links to follow and which to ignore.

They also control a number of other factors, such as how long to crawl each page and how often crawlers should check back to check for new updates.

More Helpful Reading: https://www.fannit.com/blog/google-ranking-check/ 

Remember, the websites deemed important enough for crawlers to spend a lot of time on tend to get a higher ranking on relevant SERPs.

The more your website appeals to a crawler the higher up it will appear in Google’s results.

Let’s take a look at the different factors web crawlers and bots consider when crawling for data.

what is a web crawler

How Does Web Crawling Work?

First of all, a crawler checks if a website is authoritative. Some pages and websites have more reliable data than others after all.

This is why crawlers do not sort through every single page on the internet and do not need to. 

But, how is a crawler able to tell which ones are reliable, ample sources of information, and which sites are duds?

There are a number of markers that can give away a website’s importance to crawlers.

These may be based on how many pages link back to it, the amount of traffic the site receives, and anything else the search algorithm coder deems to be important.

All these together mean that the sites a crawler indexes for its search engine are more likely to be authoritative, contain high-quality data and information, and be useful for users.

These are the sites that a crawler will prioritize and are likely to find themselves at the top of the search results.

How Often Should a Website Be Crawled?

As we mentioned before, the internet is constantly changing. 

Websites are updated, and web data is edited every day, not to mention the creation of new platforms.

If a search engine wants to continue to provide relevant and useful information to its users, it needs to constantly monitor websites for any changes which might affect their indexing.

The importance of the website is also a crucial factor in deciding how often a web crawler should revisit a page.

Authoritative and reliable pages are likely to have the best and most up-to-date information, so a standard web crawler will want to keep checking back.

What Are a Web Crawler’s Robots.txt Requirements?

One way that a web crawler makes a choice about what page to the index is by using something called a robots.txt file.

A robots.txt is a file hosted by the target website and includes certain rules for any visiting crawler to that website. 

The robots.txt rules define what pages it allows a spider bot to crawl and if it allows them to follow a certain link or not.

Here’s how major search engines use robots.txt files. 

If there is no robotx.txt file, then the spider will proceed to crawl your website as normal, as you have not stipulated any restrictions.

If there is a robots.txt file, then of course, it will follow any instructions there. 

However, if your robots.txt has errors within it then a web crawler may not crawl that website, so it will not be indexed.

Why Do Many Websites Use a Robots.txt File?

So why do some web pages use a robots.txt file that allows what a web crawler can and cannot do on their site? 

There are many reasons they may consider when writing the robots.txt file and deciding if you want a spider to crawl your page based on factors such as server resources and page relevance.

Do You Have Enough Server Resources?

First of all, whenever someone accesses a website they create requests that the web server has to respond to. This uses the server’s resources. 

It’s no different for a bot.

When a bot tries to crawl a website to index it, it also sends a request to the server to download data using its resources.

For some web servers that do not have the bandwidth to cope with multiple requests at once, it may be wise for them to deny web crawling on their site.

Otherwise, multiple crawlers cause the webserver to drastically slow down, crash, or drive up bandwidth costs as crawlers attempt to download too much data at once.

search engines crawler

Restricting Access to Irrelevant or Confidential Web Pages

There could also be pages and data that the website owners do not want the crawler to have access to. 

Perhaps it could be because they have their own search function on the site. It makes sense for them to stop their internal search results from ending up on the search engine results page.

Maybe they currently have an ongoing marketing campaign, such as a discount voucher, and only want to direct certain people onto specific pages that contain different discounts. 

They wouldn’t then want just anyone turning up on the discount page because it showed up on a search engine, so they would bar crawling to this page.

As the website owner in this scenario, you’d be able to decide if the page gets crawled or not. 

Making Efficient Use of a Web Crawler’s Time

Another point is that a search engine’s web crawler bots have their own set of instructions. This dictates what pages they search, which sites to revisit, and importantly for robots.txt, how long to crawl them for.

This is important because a crawler may have a set URL budget. This determines how long it spends crawling a particular site in order to save resources.

You, therefore, want to make sure that a web crawler does not waste its allocated time on your website crawling through irrelevant pages you do not need to be seen.

Robots.txt files can help here by directing crawlers to the right pages. In other words, you can tell bots what parts of your site should appear on relevant search engine results pages. 

In major search engines, web crawler bots do the following:

Site Crawling

First of all, they crawl online for the content, data, and information search engines need, scouring each site’s HTML code and the content on it.


Once the online web content and data have been found, the web crawler will index it into different categories based on content, making it readily available to show up at the next relevant query.


Not only do they rate URLs based on what information they contain for different categories, but a crawler also advises on how highly they should be ranked based on relevance, quality, user experience, and more.

How Can Web Crawling Help Your SEO (Search Engine Optimization)?

We’ve discussed what web crawlers, bots, or spiders are and how they work.

But why do you and your marketing team need to know about them?

The reason is that a better understanding of how these web crawler bots work will give you insight into how to improve your website’s SEO, pushing it up the search results rankings.

So how can you use a web crawler Google strategy to boost your SEO?

More Helpful Reading: https://www.fannit.com/seo/technical-seo/

Manage Your Robots.txt Restrictions

First of all, remember the robots.txt file. 

While some people use robots.txt to block crawlers from crawling and indexing their page if you want to improve your SEO make sure you do not do this.

If a web crawler can’t search your page and index it, it will not even show up in the search engine’s results, where no one will find it.

Therefore, when writing your website’s robots.txt file, make sure that all the pages you want to be found are actually accessible to web crawling.

This will ensure they will all be properly searched and indexed, giving them a chance to appear on the search engine’s results page.

Don’t Forget About a Web Crawler’s Own Restrictions

Restrictions aren’t just placed by those hosting a server. The owners of a crawler also use restrictions to make sure they only crawl web pages that are relevant and don’t get bogged down on secondary ones.

Google, for example, restricts its bots in: what pages to scan, how often to crawl, and how much pressure to put on a server.

Do Your Backlink Outreach

This is why it’s so helpful for your SEO to get as many backlinks to your URLs out there as possible.

There are a few ways you can do this, such as pushing out online content that has links within the text or images. 

Investing in some PR can help too, as it can get your web content with the ingrained links on multiple websites belonging to different media outlets.

Another factor was website traffic, or how many views your page gets. 

Understanding crawling strategies and using other marketing methods to drive users to your site will therefore help your SEO a lot.

Of course, the more your SEO improves, the more you’ll increase traffic to your site, helping to create a cycle of great reach!

More Helpful Reading: https://www.fannit.com/seo/free-backlinks/

How Using a Web Crawler Can Help Your Marketing

While content-focused web crawlers are predominantly used by search platforms, not all are.

In fact, there are many publicly available paid or free open-source web crawlers available online that you could use to assist your marketing strategy. So how does this work?

web crawler google

Evaluate Your Website

First of all, your web crawler can evaluate your website, analyze its performance, and compare it to competitors. It can also show you how search platforms see your pages.

If you use a spider on your own website you can therefore see if your pages have a good technical performance and if not, what areas are in need of improvement.

Check on Your Competitors

Of course, you could also do the same with your competitors’ sites to check on who’s outperforming who.

Knowing which factors you need to improve over your main competitors can help give you an edge.

If you want to do a quick check to see if Google’s web crawler is even reading your website. 

Why Isn’t My Website Being Crawled?

The first thing to do is to make sure that your entire site is being indexed, then install Google Search Console, and learn to request a crawl through there. 

Moreover, this may also be due to your pages being too new, meaning a web crawler has not had a chance to crawl them yet.

Maybe no other external site is linking back to your website. This is a pretty important factor for search platforms, so you need to invest in backlink outreach with other websites.

If your site has a poor user experience and is difficult to navigate, it might have made it too hard for the spider to crawl it properly, leading it to be improperly indexed.

Also, make sure you do not use tactics that could be viewed as spam on your site, as this will cause you to be blacklisted from Google.

How to Ensure Web Crawlers Can Find Your Webpages

So what can you do to make sure the pages you want to be found actually end up on a search engine’s results page? 

You may find that Google or another search engine can find your website but is not displaying all the pages on the site, even if they’re important.

Here’s what you can check for:

Is the Web Crawler Being Blocked by Your Login Forms?

First of all, does your website use login forms? 

If any content or information is hidden behind a login page, a web crawler may not be able to access it.

After all, the bot itself won’t set up its own account!

Search Engine Crawlers Cannot Use Search Bars Themselves!

Also, do not try to use an internal search bar and expect people to simply use this to find pages on your site rather than links.

Not only is this not the most user-friendly experience, but also bots do not know how to crawl through a search bar.

All they know to do is crawl through links to new pages, so if your landing page has no links to the rest of your site, the web crawler will not explore the rest of it.

Web Crawlers Prefer Text to Images, Video, or Other Media

In recent times, search platforms and their web crawlers have made headway with image search, and this is still improving.

However, it’s not yet perfect, and search platforms still prefer to crawl through text.

This is why you need to find a balance and write for both users as well as bots if you want your page to rank. 

Do not place your text inside of images, videos, or GIFs if you want the web crawler to read it and index it.

It’s still beneficial to have visual elements on your site. But make sure the actual text is included within your HTML code. 

Otherwise, it will not show up on a results page as the crawler won’t index it.

Using a Web Crawler for Maintenance

A web crawler could also be used for simple site maintenance. It will help show you which links are working and if your HTML code is valid.

This will keep your pages running smoothly and improve the user experience. 

The better the user experience, the more time they’ll spend on the page, and the more likely they’ll be to return, all of which help improve your SEO.

Using Web Crawling to Improve User Experience

Google rewards pages that deliver a good user experience with improved positions in its rankings.

If your page is easy to navigate and provides the information that meets the search intent, Google’s crawlers will give it a higher preference.

Content is a valuable resource for all websites. It helps engage your audience, bring new users in, and expand your reach when it is widely shared.

But it’s not just users who are reading it. It’s also the bots who are in charge of web crawl duties.

The way that web crawlers analyze content directly influences your search engine rankings.

You should make sure your web content is produced with web crawling in mind. 

Web Crawling and Web Scraping

You may have seen web crawling and web scraping being used interchangeably, but these processes are actually different. 

While web crawlers keep on following URLs from site to site in perpetuity, web scraping is actually much more focused and targeted.

Also called content scraping and data scraping, the web scraping process can actually revolve around one website or even just a particular page.

Web Scraper Bots that Copy Data

The other difference is the extent and purpose of the data extraction. 

While a web crawler merely collects the data for indexing purposes, the process of web scraping will actually copy the data and download it to another site.

Web scraping does not just gather metadata and other unseen information like web crawling. Instead, web scrapers actually perform data extraction content to be used on another site.

These can consist of specific elements within the site or entire downloaded pages. Scrapers collect data from private pages and public websites alike, storing huge amounts of information about all the URLs they visit. 

Web Scrapers Ignore Robots.txt Restrictions

Finally, web scraping bots do not follow the requirements on a page’s robots.txt, so could end up straining the server’s bandwidth.

This is because web scraping does not seek the website owners’ permission; instead, it will just download its content and data without checking its robots.txt.

Web scraping is commonly used for malicious purposes, which could include spam or data theft.

Malicious web scraping bots, therefore, need to be blocked.

If not, a server could fall victim to theft, the user experience can be severely hurt, and the website could even crash completely.

It is possible to block web scraping bots from accessing a website. 

However, you need to be careful your robots.txt filters out the harmful web scraper attacks yet still allows a legitimate crawler to browse.

This will protect the server without harming the website’s SEO.

What Are the Different Types of Web Crawlers?

So now we know what web crawlers do, how they work, and how they differ from web scraping. 

Next, let’s take a look at some of the different types of bots that search platforms use today.

As mentioned earlier, the most common users of web crawlers are search engines, using them to crawl and index pages across the internet. 

Here are the ones used by the biggest:

Google – Googlebot

Googlebot is Google’s main crawler but is actually composed of at least two web crawlers.

These are Googlebot Mobile and Googlebot Desktop, designed for browsing the different platforms to index both kinds of sites.

With this in mind, it’s important to make sure your website is mobile-friendly for easy crawling by Googlebot Mobile, as this will help boost search rankings.

The search giant also uses a number of other web crawler browser bots for different purposes.

These include Googlebot Images, Googlebot Videos, Googlebot News and AdsBot.

All of these have a specific type of content they focus on as their names suggest.

Bing – Bingbot

Bingbot is the main web crawler for Microsoft’s Bing. It covers most of Bing’s everyday crawling needs.

However, Bing does use a few more specific crawlers, much like Google. This are:

BingPreview which is used to generate page snapshots and has both desktop and mobile variants. AdidxBot crawls ads and follows through to the sites linked in those ads. And MSNBot was originally Bing’s main web crawler but has since been relegated to minor crawl duties

Baidu – Baidu Spider

Baidu is the main search engine in China and is actually the fourth largest website according to the Alexa Internet Rankings, so it has a huge number of users.

Google is unavailable in China, so if you’re looking to expand your marketing into the country, a good knowledge of how Baidu Spider works will help make sure Baidu will index your site.

One thing to remember is that it will have high latency when crawling a site hosted outside of China, hurting its SEO as crawlers do not like a slow website.

You can mitigate this by using a Content Delivery Network on your website. This will help speed up your site for Chinese users, making it easier for Baidu Spider to crawl through your pages without getting slowed down.

There are other slight differences too. For example, Baidu Spider focuses mostly on home pages, while Googlebot places more relevance on internal pages.

Baidu Spider also prefers fresh content and information rather than long, in-depth articles.

Yandex – Yandex Bot

Yandex is Russia’s main search engine, and it uses its own web crawler, Yandex Bot.

The platform has more than 60% of the market share for search engines in Russia so if you want to target Russian users it’s worth getting to know this bot and making sure it’s given permission to crawl your sites. 

This allows it to index your webpage without getting blocked.

Want to Leverage Web Crawling and Other Techniques to Boost Your SEO Marketing? Contact Fannit Today

Search engines are probably the most important tool on the internet and available to all.

They are the main conduit for digital information and how the majority of users consume data on the internet. 

Therefore, their importance for digital marketing cannot be understated if you want users to find your products and services, you simply have to make use of search engines.

In order to use search engines effectively, then it is crucial you understand how their main tool, web crawlers, works.

A thorough understanding of crawlers and bots will help guide you to optimize your site and content to make them as web crawler friendly as possible and ensure that these bots will index all your pages.

At Fannit, we have plenty of experience in SEO marketing, and we know how to take advantage of web spiders and their crawling processes. 

If you want help to make your website and content perfect for a crawler to read, index, and hit the top spot on Google’s search results, then contact Fannit today.

More Helpful Reading: http://carl.cs.indiana.edu/fil/Papers/crawling.pdf

Keith Eneix

My brother Neil and I founded Fannit in 2010 and set out to help entrepreneurs just like us achieve their dreams of being successful business owners. It’s been a rewarding journey for us, and we love every day of it. Inside of Fannit, I work with both our internal team and our clients to make sure that we have everybody working the right roles and we’re being as efficient as possible as a team. I’m always happy to step in whenever there is a difficult SEO challenge at hand... it’s the element of marketing that I’m most passionate about. We’re all here to get better and grow, and that’s what gets me up in the morning! Connect with me on LinkedIn >