A crawler, also known as a web spider or web robot, is an automated program that searches the Internet to find, read and index websites.

By systematically browsing the web, crawlers collect information about websites, which is then used by search engines to catalog the content and make it available in search results. Crawlers are crucial for the functioning of search engines, as they help to organize the immense volume of information on the Internet and make it accessible.

This makes it a crucial aspect that we need to understand if we want to understand how on-page optimization works as an example.

But what exactly are the roles of crawlers in search engine optimization?


The role of crawlers in search engine optimization

Crawlers play a central role in search engine optimization (SEO). They determine which pages are found on the Internet and how they are displayed in the search results. It is therefore essential for website operators to make their pages crawler-friendly in order to achieve good visibility in the search results. This includes optimizing the website structure, providing relevant and high-quality content and implementing meta tags that help the crawlers to index the page correctly.


How crawlers work

In order to use crawlers for us, we need to understand how they work.

Crawling process in detail

The crawling process begins when a crawler receives a list of web addresses (URLs) that serve as a starting point. This start list is often obtained from previous crawling runs, sitemaps, or from external links on other websites. The crawler visits each URL, reads the contents of the page and collects links to other pages. The crawler then adds these new URLs to its list and repeats the process. During crawling, pages are evaluated according to various criteria, such as topicality, relevance and authority, which influence indexing and ranking in the search results.

How crawlers index websites

After a crawler has visited a website and read its content, the page is indexed. This means that the information on the page is stored in the database of a search engine. Indexing enables the search engine to display the page as a result for relevant search queries. During indexing, crawlers extract important information from the page, such as text content, images, videos and meta tags. This information helps the search engine to understand what the page is about and for which search queries it could be relevant.


Types of crawlers

Basically, there are 3 types of crawler:


  1. Web crawler
  2. Focus crawler
  3. Hybrid crawler


But what makes them different?

Web crawler

Web crawlers are the most common type of crawlers that search the entire Internet to find, index and update web pages. They are designed for general purposes and form the backbone of search engines such as Google, Bing or Yahoo. Their main task is to continuously search the web for new or updated pages in order to keep the search engine databases up to date.

Focus crawler

Focus crawlers differ from general web crawlers in that they concentrate on specific subject areas or industries. They are programmed to identify and collect websites that contain certain keywords, phrases or topics. Focus crawlers are often used by research organizations, academic institutions or specialized search engines to more efficiently find relevant information within a specific area of interest.


Hybrid crawler

Hybrid crawlers combine features of web crawlers and focus crawlers. They use sophisticated algorithms to search the Internet for general information, but can also search for content within specific subject areas. Through the use of artificial intelligence (AI) and machine learning (ML), hybrid crawlers dynamically adapt to their search targets, improving their efficiency and accuracy over time.

Importance of crawlers for SEO

Crawlers therefore have a direct influence on the ranking of a website in the search results. Websites that are well optimized for crawlers have a higher chance of being discovered, indexed and positioned well in the search results. Factors that influence the crawling and thus the ranking include the website structure, the speed of the page, the relevance of the content, the quality of the incoming links and the correct use of meta tags.

We summarize even more ranking criteria here: On Page Optimization.

Websites that are regularly updated and offer high-quality, relevant content are preferred by crawlers and generally receive better rankings.

To optimize a website for crawlers and improve the SEO ranking, webmasters should observe the following best practices:


  • Submit sitemaps: An XML sitemap helps crawlers to understand the structure of a website and to capture all pages efficiently.
  • Robots.txt: This file specifies which areas of a website should not be crawled, which improves the efficiency of the crawling process.
  • Responsive design: A mobile-friendly website is preferred by search engines as more and more users are accessing the Internet via mobile devices.
  • Optimize loading times: Fast loading times improve the user experience and are rated positively by search engines.
  • High-quality content: Regular updates with relevant and high-quality content attract both users and crawlers.
  • Internal linking: A smart internal linking strategy helps crawlers understand the relevance and hierarchy of pages and promotes deeper indexing.


The future of crawlers

The future of web crawlers lies in the further development of the technologies that drive them. With advances in artificial intelligence (AI) and machine learning (ML), crawlers are becoming increasingly intelligent. They become better at understanding content in context, evaluating the relevance of information and even searching complex websites more efficiently. In addition, crawlers are expected to use more advanced algorithms to deliver personalized search results based on user behavior and preferences.

The further development of crawlers and their adaptation to new technologies will be decisive for how information is organized and made accessible on the web. For SEO experts and webmasters, this means that they need to stay up to date and continuously optimize their websites to keep up with the changes and ensure their visibility in search results.