Web crawlers (also called spiders or bots) are programs used by search engines to discover and catalog web pages. They follow links from page to page, building an index of content.
How web crawlers work
- Discover: Find URLs from sitemaps and links
- Request: Download page content
- Parse: Extract text, links, and metadata
- Store: Add content to the index
- Follow: Visit linked pages
Major web crawlers
- Googlebot: Google's crawler
- Bingbot: Microsoft's crawler (also powers Yahoo Search)
- DuckDuckBot: DuckDuckGo's crawler
Crawl budget
Search engines allocate a limited "budget" for crawling each site:
- Large sites may not have all pages crawled
- Important pages should be easily discoverable
- Fast servers allow more pages to be crawled
Managing crawlers
- robots.txt: Control which pages can be crawled
- Meta robots: Page-level control
- Sitemaps: Help crawlers find important pages
- Internal linking: Ensure pages are discoverable
How VitalSentinel handles this
Crawlers are how search engines find your revenue, so anything that blocks them is a silent emergency. VitalSentinel pairs Robots.txt Monitoring with Indexing Monitoring to watch both sides of the crawl: what you tell bots they can fetch, and what Google actually keeps in its index. You find out in hours, not weeks, when a directive change or a noindex tag starts pulling pages out of search results.
Related Terms
Google Search Console
A free tool from Google that helps website owners monitor, maintain, and troubleshoot their site's presence in Google Search results.
Indexing
The process by which search engines store and organize web content so it can be retrieved and displayed in search results.
robots.txt
A text file at the root of a website that tells search engine crawlers which pages or files they can or cannot request from the site.
Sitemap
A file that lists all the URLs of a website that should be indexed by search engines, helping crawlers discover content.