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Web Crawler 101: What Is a Web Crawler and How Do Crawlers Work?

Search engines are the gateway of easy-access information, but web crawlers, their little-known sidekicks, play a crucial role in surfacing and rounding up content around the web. Plus, they are essential to your search engine optimization (SEO) strategy.

What is a web crawler?

All in one icon with four dots with lines from each connecting them in the center.

Web Crawler defined

A web crawler, also referred to as a search engine bot or a website spider, is a digital bot that crawls across the World Wide Web to find and index pages for search engines.

Search engines don’t magically know what websites exist on the Internet. The programs have to crawl and index them before they can deliver the right pages for keywords and phrases, or the words people use to find a useful page.

Think of it like grocery shopping in a new store.

You have to walk down the aisles and look at the products before you can pick out what you need.

In the same way, search engines use web crawler programs as their helpers to browse the Internet for pages before storing that page data to use in future searches.

This analogy also applies to how crawlers travel from link to link on pages.

You can’t see what’s behind a can of soup on the grocery store shelf until you’ve lifted the can in front. Search engine crawlers also need a starting place — a link — before they can find the next page and the next link. Screenshot of Link Paths for Web Crawlers Full width

How does a web crawler work?

Search engines crawl or visit sites by passing between the links on pages. However, if you have a new website without links connecting your pages to others, you can ask search engines to perform a website crawl by submitting your URL on Google Search Console.

You can learn more about how to check if your site is crawlable and indexable in our video!

Crawlers act as explorers in a new land.

They’re always looking for discoverable links on pages and jotting them down on their map once they understand their features. But website crawlers can only sift through public pages on websites, and the private pages that they can’t crawl are labeled the “dark web.”

Web crawlers, while they’re on the page, gather information about the page like the copy and meta tags. Then, the crawlers store the pages in the index, so Google’s algorithm can sort them for their contained words to later fetch and rank for users.

What are some web crawler examples?

So, what are some examples of web crawlers?

Popular search engines all have a web crawler, and the large ones have multiple crawlers with specific focuses.

For example, Google has its main crawler, Googlebot, which encompasses mobile and desktop crawling. But there are also several additional bots for Google, like Googlebot Images, Googlebot Videos, Googlebot News, and AdsBot.

Here are a handful of other web crawlers you may come across:

  • DuckDuckBot for DuckDuckGo
  • Yandex Bot for Yandex
  • Baiduspider for Baidu
  • Yahoo! Slurp for Yahoo!

Bing also has a standard web crawler called Bingbot and more specific bots, like MSNBot-Media and BingPreview. Its main crawler used to be MSNBot, which has since taken a backseat for standard crawling and only covers minor website crawl duties now.

Why web crawlers matter for SEO

SEO — improving your site for better rankings — requires pages to be reachable and readable for web crawlers. Crawling is the first way search engines lock onto your pages, but regular crawling helps them display changes you make and stay updated on your content freshness. Since crawling goes beyond the beginning of your SEO campaign, you can consider web crawler behavior as a proactive measure for helping you appear in search results and enhance the user experience.

Keep reading to go over the relationship between web crawlers and SEO.

Crawl budget management

Ongoing web crawling gives your newly published pages a chance to appear in the search engine results pages (SERPs). However, you aren’t given unlimited crawling from Google and most other search engines.

Google has a crawl budget that guides its bots in:

  • How often to crawl
  • Which pages to scan
  • How much server pressure is acceptable

It’s a good thing there’s a crawl budget in place. Otherwise, the activity of crawlers and visitors could overload your site.

If you want to keep your site running smoothly, you can adjust web crawling through the crawl rate limit and the crawl demand.

The crawl rate limit monitors fetching on sites so that the load speed doesn’t suffer or results in a surge of errors. You can alter it in Google Search Console if you experience issues from Googlebot.

The crawl demand is the level of interest Google and its users have on your website. So, if you don’t have a wide following yet, then Googlebot isn’t going to crawl your site as often as highly popular ones.

Roadblocks for web crawlers

There are a few ways to block web crawlers from accessing your pages purposefully. Not every page on your site should rank in the SERPs, and these crawler roadblocks can protect sensitive, redundant, or irrelevant pages from appearing for keywords.

The first roadblock is the noindex meta tag, which stops search engines from indexing and ranking a particular page. It’s usually wise to apply noindex to admin pages, thank you pages, and internal search results.

Another crawler roadblock is the robots.txt file. This directive isn’t as definitive because crawlers can opt out of obeying your robots.txt files, but it’s handy for controlling your crawl budget.

Optimize search engine website crawls with WebFX

After covering the crawling basics, you should have an answer to your question, “What is a web crawler?” Search engine crawlers are incredible powerhouses for finding and recording website pages.

This is a foundational building block for your SEO strategy, and an SEO company can fill in the gaps and provide your business with a robust campaign to boost traffic, revenue, and rankings in SERPs.

Named the #1 SEO firm in the world, WebFX is ready to drive real results for you. With clients from a range of industries, we have plenty of experience. But we can also say that our clients are thrilled with their partnership with us — read their 1,100+ testimonials to hear the details.

Are you ready to speak to an expert about our SEO services?

Contact us online or call us at 888-601-5359 today — we’d love to hear from you.

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