Crawler
Definition
A crawler, also known as a web spider or bot, is an automated program used by search engines to systematically browse the internet. Its primary function is to discover and scan webpages, collecting data to be stored and indexed for use in search results. Crawlers follow links from one page to another, building a map of websites and their relationships.
For businesses, crawlers are critical because they determine how search engines see and interpret content. If a site is not effectively crawled, important pages may not be indexed, reducing visibility and limiting organic traffic opportunities.
Advanced
Crawlers operate by sending HTTP requests to servers, downloading HTML and resources, and analyzing elements such as meta tags, structured data, and internal linking. They respect directives like robots.txt, nofollow attributes, and canonical tags to determine what should or should not be indexed.
Search engines manage crawl budgets to decide how often and how deeply a crawler visits a site, which is particularly important for large websites. Advanced SEO teams use log file analysis and crawl simulation tools to study crawler activity, optimize site performance, and ensure important pages are prioritized for indexing.
Why it matters
Use cases
Metrics
Issues
Example
An e-commerce site launches thousands of new product pages. Googlebot begins crawling them, but only a portion is indexed due to limited crawl budget. By improving site structure and prioritizing high-value URLs, the company increases crawl efficiency and boosts organic visibility.