Crawler (Web Crawler / Spider / Bot) is a bot program that automatically crawls web pages, collects their content, and processes it into the search engine database.
The best-known crawlers:
- Googlebot: Google’s crawler; it also has subtypes such as Googlebot Smartphone (mobile) and Googlebot Image.
- Bingbot: Microsoft Bing’s crawler.
- YandexBot: Yandex’s crawler.
- Baiduspider: Baidu’s (China) crawler.
- SEO tools (Ahrefs, Semrush, Moz) and social media bots (FacebookExternalHit) also use their own crawlers.
How a crawler works:
- It starts from a known URL (sitemap, previously crawled pages)
- It downloads the page and analyzes the HTML
- It adds all links on the page to the queue
- It visits new URLs while following the robots.txt rules
- It sends the content it finds to the index database
Tip: Monitor Googlebot visits in your server logs. Which pages are crawled and how often can tell you a lot about your site’s technical health.