web crawler
A web crawler is a program that systematically browses the web by following links, collecting data from pages it visits.
A web crawler (also called a spider or bot) is a program that systematically browses the web by following hyperlinks from page to page. It starts from one or more seed URLs, downloads the page content, extracts links, and then visits those linked pages. This process repeats until the crawler reaches a defined limit or runs out of new URLs to visit.
How web crawlers work
A typical web crawler follows this cycle:
- Start with a seed URL
- Download the page and parse its HTML
- Extract all links from the page
- Add new, unvisited links to a queue
- Pick the next URL from the queue and repeat
Crawlers track which URLs they have already visited to avoid infinite loops. They respect robots.txt rules and may throttle their request rate to avoid overloading servers.
Types of web crawlers
- Search engine crawlers - Googlebot, Bingbot, and others that build the search engine index
- SEO crawlers - Tools that audit websites for technical SEO issues
- Data collection crawlers - Programs that extract specific data for research or analysis
- Monitoring crawlers - Bots that check for uptime, content changes, or security issues
How crawler.sh works
crawler.sh is an SEO-focused web crawler built in Rust for speed and low memory usage. It performs breadth-first crawling within a single domain, recording status codes, redirects, meta tags, and content for every page. The crawl data can be analyzed with crawler info for statistics, crawler seo for SEO issues, and exported to JSON or sitemap XML formats.
