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What is a Web Crawler?

What is a Web Crawler?

I don’t know about you, but I wouldn’t describe myself as a “technical” person. In fact, the technical aspects of marketing are usually the hardest ones for me to conquer.

When it comes to technical SEO, it can be difficult to understand how the process works. But it’s important to gain as much knowledge as we can to optimize our websites and reach larger audiences. One tool that plays a large role in search engine optimization is none other than the web crawler.

In this post, we’ll learn what web crawlers are, how they work, and why they should crawl your site.

Free Guide: How to Run a Technical SEO Audit



You might be wondering, “Who runs these web crawlers?”

Usually, web crawlers are operated by search engines with their own algorithms. The algorithm will tell the web crawler how to find relevant information in response to a search query.

A web spider will search (crawl) and categorize all web pages on the internet that it can find and is told to index. So you can tell a web crawler not to crawl your web page if you don’t want it to be found on search engines.

To do this, you’d upload a robots.txt file. Essentially, a robots.txt file will tell a search engine how to crawl and index the pages on your site.

For example, let’s take a look at for visual learners.

Nike robots.txt to instruct web crawler what to index

For Nike, it used its robot.txt file to determine which links in its website would be crawled and indexed.

Nike robots.txt file instructing web crawler to allow seven pages to be crawled and disallow three

In this portion of the file, it determined that:

  • The web crawler Baiduspider was allowed to crawl the first seven links
  • The web crawler Baiduspider was disallowed to crawl the remaining three links

This is beneficial for Nike because some pages the company has aren’t meant to be searched, and the disallowed links won’t affect its optimized pages that help them rank in search engines.

So now that we know what web crawlers are, how do they do their job? Below, let’s review how web crawlers work.



A search engine’s web crawler most likely won’t crawl the entire internet. Rather, it will decide the importance of each web page based on factors including how many other pages link to that page, page views, and even brand authority. So, a web crawler will determine which pages to crawl, what order to crawl them in, and how often they should crawl for updates.

how web crawlers work visual chart

Image Source

For example, if you have a new web page, or changes were made on an existing page, then the web crawler will take note and update the index. Or, if you have a new web page, you can ask search engines to crawl your site.

When the web crawler is on your page, it looks at the copy and meta tags, stores that information, and indexes it for Google to sort through for keywords.

Before this entire process is started, the web crawler will look at your robots.txt file to see which pages to crawl, which is why it’s so important for technical SEO.

Ultimately, when a web crawler crawls your page, it decides whether your page will show up on the search results page for a query. It’s important to note that some web crawlers might behave differently than others. For example, some might use different factors when deciding which web pages are most important to crawl.

Now that we’ve gone over how web crawlers work, we’ll discuss why they should crawl your website.

Why is website crawling important?

If you want your website to rank in search engines, it needs to be indexed. Without a web crawler, your website won’t be found even if you search for over a paragraph directly taken from your website.

In a simple sense, your website doesn’t exist unless it’s crawled once.

To find and discover links on the web across search engines, you must give your site the ability to reach the audience it’s meant for by having it crawled — especially if you want to increase your organic traffic.

If the technical aspect of this is confusing, I understand. That’s why HubSpot has a Website Optimization Course that puts technical topics into simple language and instructs you on how to implement your own solutions or discuss them with your web expert.

Expand Your Reach With Web Crawling

Web crawlers are responsible for searching and indexing content online for search engines. They work by sorting and filtering through web pages so search engines understand what every web page is about. Understanding web crawlers is just one part of effective technical SEO that can improve your website’s performance significantly.

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