What is a crawler?
A crawler is an algorithm designed to extract specific information from websites.
For example, there are crawlers that collect email addresses, and SEO tools also use crawlers to map websites. These crawlers are created for beneficial purposes, and their usage does not have any negative impact.
The data gathered by crawlers is processed by search engine algorithms, and these are used to rank individual web pages.
A crawler starts from a pre-defined list of URLs and follows the links found on those sites. Its operation can be regulated by various parameters, which allow for actions such as:
- How deep should it follow links within a website?
- Should it follow links to other websites, and if so, how far?
- What types of files should it download, and up to what size?
- How many parallel threads should it initiate?
- How frequently should it revisit the same website?
- Should it respect the restrictions set in the robots.txt file?