Every day, invisible robots quietly scour the internet, follow links, and index billions of pages to serve us the right search results in a split second. These digital explorers, known as crawlers, are a key tool for search engines and for companies that want to be seen.
A digital explorer of the internet
A crawler, sometimes called a spider, robot, or bot, is a specialized program that tirelessly traverses the internet and follows links between pages. Its main task is to automatically collect and analyze data, for example to index new content for search engines, check website functionality, or look for specific information. It works by visiting pages in sequence, reading their content, and sending it back to a system that processes the data further. Thanks to crawlers, search engines learn about new pages, analytics tools help webmasters fine-tune their sites, and unfortunately, spammers also look for email addresses for unsolicited advertising. Whether they serve helpful or less useful purposes, crawlers are an essential part of the digital world and the internet as we know it.
Key players of the online world
Thousands of crawlers operate on the internet, but the most important include search engine robots that determine how well a website will be visible in search results. In the Czech Republic, two have the upper hand: Google’s Googlebot and Seznam’s Seznambot.
Although it may seem that search engine robots do whatever they want on the web, in reality their movement can be regulated to some extent. Website administrators can, for example, block access to an entire site or just specific parts via the robots.txt file. If you need to prevent the indexing of specific links on a page, the robots meta tag helps. For even more granular control, you can use the rel attribute with the value nofollow, which tells robots to ignore a given link.
How to control what appears in search results
Crawling a website is just the first step; what’s crucial is whether the crawler saves a page to its index. You can influence this in several ways. The simplest is again the robots meta tag, where the values index or noindex determine whether a page should be included in search. For files such as PDFs or images, the HTTP header X-Robots-Tag serves the same purpose.
Status codes also matter: if you delete a page, the 404 status code ensures its removal from the index, while the 301 status code informs the robot about its move. When managing duplicate content, canonicalization helps—specifically, the canonicalization of URL, which marks the primary version of a page and passes link equity to it. Proper indexing practices ensure that only relevant and useful pages appear in search results.
How often bots visit websites
The frequency of crawler visits depends on how important a site appears in the eyes of a search engine. Pages with high authority and regularly updated content can expect robots on a daily basis, while less significant sites may be crawled only once a week or even monthly.
Malicious bots and how to stop them
Not all crawlers are useful and beneficial. Some robots focus solely on quickly downloading a large number of pages, which can significantly burden a server, slow its response, or temporarily take it offline. There are ways to defend against these unwanted visitors.
First, it’s important to identify the malicious robot via its user agent and IP address from server logs. You can then attempt to restrict its access using robots.txt, but if it ignores this, you need to act more decisively. An effective method is blocking on the server via the .htaccess file, which ensures the malicious robot cannot load the site at all.
Try your own crawler
Want to see exactly how a crawler works in practice? Just get your own! A simple and free solution is Xenu’s Link Sleuth, which works just like search engine robots: it starts at a site’s home page, explores all links, continues further, and gradually goes through the entire site. In the end, you get a clear report of found links, including those that point to non-existent pages or are redirected. This makes it easy to fix broken links and improve your site’s trustworthiness for search engines.
Conclusion
Although we often don’t realize it, the internet would look completely different without crawlers. Every day they traverse billions of pages, organize information, and help users find what they’re looking for. If you manage a website, it’s good to understand how they work, because proper indexing and optimization can be the difference between success and obscurity. And if the world of digital robots fascinates you, you can try out how a crawler works yourself with tools that reveal what search engines see on your site.
Frequently asked questions
How do I find out whether a crawler visits my website?
You can monitor crawler activity using tools like Google Search Console, where you’ll find an overview of how often Googlebot crawls your site.
Why is a crawler important for search engines?
Crawlers are key to how search engines work because they traverse the internet, collect data about pages, and enable them to be included in the index. Without them, search engines couldn’t show current and relevant results.
How can I improve my website’s visibility for crawlers?
The most important factors are a solid site structure, proper internal linking, and fast page loading. Registering in Google Search Console and creating an XML sitemap also helps.
Useful links:
- https://en.wikipedia.org/wiki/Web_crawler
- https://www.akamai.com/glossary/what-is-a-web-crawler
- https://www.cloudflare.com/learning/bots/what-is-a-web-crawler/