What is a web crawler? (Plus definition and importance)

By Indeed Editorial Team

Published 25 April 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Search engine optimisation, a tool that marketing professionals and businesses use, encourages search engines to rank websites as highly as possible. Web crawlers directly contribute to this ranking, using algorithms and data to position websites based on their suitability and credibility. If you work in SEO, or if this career path interests you, then you can benefit from learning the answer to 'What is a web crawler?'. In this article, we look at what a web crawler is, how web crawlers work, why they're integral for SEO and how to optimise a website for crawlers.

What is a web crawler?

In answer to the question 'What is a web crawler?', it's an automated piece of code or program that indexes, identifies and categorises websites that are typically used by search engines. Also known as a spider, crawlers search the Internet for a website and scan all the content, data and keywords to determine the purpose of the website and its functionality to better rank it for search engine users. Indexing allows that website to then show up in relevant search engine results.

Related: How to become an SEO expert

Types of web crawlers

The most common type of web crawler is a search engine crawler, which is also known as a search bot. The main goal of search engine crawlers is to index content across the Internet, making it accessible to search engine users. Crawlers are also used for a range of other reasons, including:

  • data mining for addresses and information

  • web analysis

  • comparison of data on comparison websites

  • collating news and articles

  • finding faulty or incorrect content

Web crawlers and web scrapers each have different purposes. While a web crawler indexes a website without extracting any specific data, a scraper is an automated process that extracts information from websites specifically. For example, web scraping has the functionality to build databases for particular industries to gain an insight into anything from product prices to the availability of certain services.

Related: What is an SEO specialist?

How do web crawlers work?

Below, you can find a series of steps that explain how web crawlers work:

1. Request for indexing received

When you create a new website or rework an existing one, you can send a site map to search engines to let them know that your website is ready for crawling. A site map contains all the individual pages in your website, how they connect and any internal and external links included in your website. When doing this, you can also provide a crawl exclusion list to prevent crawlers from indexing certain web pages, such as if a particular page is currently offline or not completed.

Related: How to become a web designer: a step-by-step guide

2. Website discovery through external links

If you decide not to provide a site map to search engines, your website is typically found through crawling other platforms. For example, if a directory or online magazine has a link to your website, this provides access for crawlers to reach your site and index it effectively. Crawlers revisit sites multiple times and crawling happens through links and direct access. The more links to your website, the higher the priority for the crawler to index your platform as soon as possible.

3. Page importance ranked

With millions of different websites to crawl, web crawlers identify and prioritise which sites are most important for search engine users. The number of links that connect to a specific page also help in determining page importance. In addition, the number of page views is also considered to rank pages by significance to users.

4. Webpages indexed for purpose

When crawling a webpage, a web crawler records the content within the website and the meta-information to understand the purpose of your website from keywords and other relevant information. Crawlers base each page index on searchable keywords and phrases found within the copy, which places the website in a virtual list of other relevant websites to appear in search engine results. Different search engine crawlers may prioritise different keywords and re-indexing may also lead to further indexing, with the addition of more keywords and phrases.

5. Webpages cached for quick retrieval

Following initial crawling, the crawler creates a cached version of your pages to reduce the risk of slower loading speeds. A cache is a version of your website that's saved elsewhere for quick retrieval. When you look at a search engine result, it's typically a cached page you see when you click a specific link. Cached pages are regularly refreshed and updated with re-indexing and repeated crawling, but they may not be completely up-to-date if you've made very recent changes.

Why is web crawling important for SEO?

Some of the key reasons why web crawling is important for SEO include:

Providing a ranking on search engines

Crawlers catalogue and determine the keywords and links within your website to index your page and include you in search engine rankings. Without that indexing, search engines wouldn't have your website content available to rank using its internal algorithms. The relevance of your content, the keywords you use and the links to your website all impact indexing, which influences exactly where your website ranks in search results. For example, if you sell cakes and your website includes keywords for wedding cakes, cupcakes and birthday cakes, crawlers index your site to rank you correctly for search results that involve cakes.

Adjusting crawling budgets can increase page speed

Web crawlers work to a specific budget for web pages, using internal calculations and rules to determine how many pages they index in a specified period. While this search engine crawler budget is set by default, it's also possible to manually adjust that budget to suit your needs and goals. For example, a high crawl budget is important so search engines have the latest version of your website at all times.

In the case of larger websites with many external links, lowering or limiting the crawl budget can help to prevent slower loading times. By reducing crawling to a steadier level, well-connected websites can meet the needs of a high visitor volume while also keeping their site indexed and up-to-date.

Specifying crawling pages can help with priority

A crawl exclusion list is a process that involves selecting web pages you don't want crawling, which automatically brings other pages higher up the priority list. For example, if you have older pages you don't wish to prioritise, choosing to exclude them can give newer pages a better chance of high priority. If you have web pages with similar content and keywords, this can prevent two individual pages from appearing in search rankings to provide a more streamlined solution for search engine users.

How to optimise a website for crawlers

Web crawlers index your website, regardless of its complexity or layout, but there are a few practices you can follow for crawl optimisation. Here are some steps to follow to optimise your website for crawlers:

1. Create a flat page architecture

A flat page architecture refers to a website where all the pages are instantly accessible, typically from the homepage. Websites with a flat architecture are easier for crawlers to explore, which allows them to index your site far more quickly and effectively. Nested websites, where more than one link is necessary to reach a specific page, can take longer for crawlers to index.

2. Optimise internal links

Optimising internal links to flow and connect with relevant categories and information is an effective way to optimise your website for crawlers. For example, providing links to the different service pages from the homepage can make it easier for crawlers to move around the site. Removing broken and redundant links can also help to make crawling faster and easier.

Related: Digital marketing skills: definition and examples

3. Provide your sitemap to crawlers

Your website sitemap effectively acts as signposting to show bots how your platform fits together and flows. Access to a sitemap makes it easier for crawlers to navigate your website. The sitemap is typically an XML file that you can provide directly to search engine crawlers.

4. Track crawlers to identify areas of improvement

Analytics tools can provide access to the tracking of search engine crawlers and other crawlers on your website. The information you gain from monitoring this can help you to optimise your website's crawling speed over time. For example, if tracking shows that crawlers are having a particular problem with one page, this may suggest the requirement for better SEO practices to make crawling easier.


  • What is indexing? (Including how it works and tips)

Explore more articles