Joran Hofman
March 6, 2021


Web crawlers, spiders, robots, or search engine bots are simply part of a computer program written and used by search engines to update their web content or index other websites' web content.

Crawling is when a search engine submits a bot to a page or web post, and they "read" the page. This allows crawlers to determine what is on the page. Don't confuse this with having that page indexed.

How Do Web Crawlers Work?

The Internet changes and expands. Since it is impossible to know the total number of web pages on the Internet, web crawlers start from a seed or a list of known URLs. First, they crawl the web pages at those URLs. Depending on the crawling of those web pages, they will find hyperlinks to other URLs and add them to the pages that they will crawl.

This process could be running almost indefinitely due to the large number of web pages on the Internet that could be indexed for your search. However, a web crawler follows certain policies that make it more selective about which pages to crawl, the order to do so, and how often they have to be crawled again for updates. The process goes as follows:

Discovering URLs

First, the search engine must have previously crawled a website. The search engine can then find a web page by following a link from a page that has already been crawled. The owner of a website can also request the search engine crawl a URL by delivering the sitemap.

Browsing a list of seeds

The search engine gives its crawlers a list of addresses (known as seeds) to review. The crawlers visit each one of the addresses, identify all the existing links on that page and add them to the list of URLs to visit.

Adding to the index

As crawlers visit the seeds in their lists, they locate the content and add it to the dictionary. This dictionary is where the search engine stores all its knowledge of the internet.

Update the index

Crawlers look for key signals to try to understand what a page is about.

Tracking frequency

Crawlers search and crawl the internet 24/7, but for individual page crawling, they consider factors such as demand, changes made to the page since their last visit, and level of interest from other search engines on the page.

Blocking trackers

You can choose to block trackers from indexing a site.

Using “Robots.txt” protocols

Robots.txt protocols can be used to communicate with crawlers, which always check the Robots.txt file of a page before entering it. Various rules can be included in this file, such as which pages to crawl, which links to follow.

These factors are weighted differently in the proprietary algorithms that each search engine embeds in its spider bots. The web crawlers of different search engines behave slightly differently. However, the end goal is the same: to download and index content from web pages.

What Are Different Types Of SEO Crawlers?

There are two types of SEO trackers: desktop trackers and cloud-based trackers.

Desktop trackers

Desktop trackers are the ones that are installed on your computer; they are inexpensive but have their disadvantages:

  • They consume memory and CPU.
  • Their collaboration is limited.
  • They offer fewer features or options than cloud-based trackers.
  • It is difficult for them to compare follow-ups and schedules.

Cloud-based trackers

Cloud-based trackers use the computing power of the cloud to offer greater flexibility and scale. Most of them allow online collaboration, dedicated live support. It is easier to notice changes between several crawls. They are generally more powerful than desktop ones. Some have basic data display features, but they are more expensive than desktop ones.

How To Recognize A Web Crawler?

Search engine trackers crawling a website are identified from the user agent field. They deliver to a web server when they request web pages. In this field, you can also include a URL where website administrators can get more details about the crawler. Using this information, website administrators examine their website's log and use it to determine which trackers have visited the website and how often.

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