Glossary

Web Crawler

An automated program that systematically browses the web to discover and index content.

Definition

A web crawler (also called a spider or bot) is an automated program that systematically browses the World Wide Web by following links from page to page, downloading and analyzing content, and feeding information back to a search engine's index. Google's crawler is called Googlebot. Crawlers discover new pages, detect content changes, and update the search index regularly. The rate and depth at which a crawler visits a site is called its 'crawl budget'.

Why It Matters

Understanding how web crawlers work is fundamental to technical SEO. If a crawler cannot access, render, or understand your content, that content cannot be indexed or ranked. Issues like blocked resources in robots.txt, slow page load times, broken internal links, and JavaScript rendering problems all impede effective crawling. Ensuring your site is crawler-friendly through proper internal linking, sitemaps, and technical configuration is a prerequisite for SEO success.

Examples

GooglebotGoogle's official web crawler that discovers and indexes pages for Google Search

Crawl budgetGoogle allocates a limited number of crawl requests per site per day — large sites with many pages must prioritize crawl efficiency

Robots.txtA file that tells crawlers which pages they are allowed or disallowed from accessing

Common Mistakes

Blocking important pages in robots.txt accidentally during development and not reverting before launch.

Not creating XML sitemaps — sitemaps guide crawlers directly to important pages.

Having too many orphan pages — crawlers primarily discover pages through internal links.

Ignoring JavaScript rendering — some crawlers struggle to render client-side JavaScript content.

Related Tools

Word Counter

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Meta Description Length Checker

Check if your meta description is the ideal length for Google.

Related Terms

Indexing

The process by which search engines store and organize web page content in their database.

Technical SEO

The optimization of a website's technical infrastructure to improve crawlability and indexing.

XML Sitemap

A file that lists all important pages on a website to help search engines crawl and index them.

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