Introduction to Web Crawling
Search engines use automated programs called crawlers (also known as spiders or bots) to systematically browse the internet. These crawlers follow links from page to page, building an index of all the content they discover. Understanding how crawling works is fundamental to ensuring your website appears in search results.
The Crawling Process
When a crawler visits your website, it goes through several steps. First, it checks your robots.txt file to understand which pages it is allowed to access. Then, it fetches the HTML of each allowed page, parses the content, extracts links, and adds newly discovered URLs to its queue for future crawling.
Discovery Methods
Crawlers discover pages through multiple channels:
- Following links from other indexed pages
- Reading XML sitemaps submitted through search console tools
- Processing redirects from old URLs to new destinations
- Revisiting previously crawled pages to check for updates
Crawl Budget
Each website receives a limited crawl budget, meaning search engines will only crawl a certain number of pages per visit. Large sites with millions of pages need to be especially careful about making their most important content easily discoverable within the first few levels of their site architecture.
Common Crawling Issues
Several technical problems can prevent search engines from properly crawling your website. Broken links lead to dead ends. Redirect chains waste crawl budget. Pages blocked by robots.txt may be the ones you actually want indexed. Orphaned pages with no internal links pointing to them may never be discovered at all.
How to Diagnose Problems
The best approach is to run a site crawl using a dedicated SEO crawler tool. This simulates what search engines do and reports on all the issues it finds, from broken links to missing meta tags to duplicate content. Regular crawls help you catch problems before they impact your rankings.
Conclusion
A well-maintained website with clean internal linking, proper sitemaps, and no technical errors will be crawled more efficiently. This translates directly into better visibility in search results and more organic traffic to your most important pages.
Related reading: See our perfect SEO example page for a checklist of all the elements a well-optimized page should have.