Web Crawler
Automated programme that systematically visits web pages, captures their content, and processes it for search engines or other services.
Also known as: Spider, Bot, Robot
A web crawler is a programme that traverses the web from link to link, fetches HTML content, and transfers it into its own database. Search engines such as Google, Bing, or Yandex use crawlers to keep their index up to date. SEO tools, price comparison services, and web archives also work with crawlers.
How it works in detail
A crawler starts with a list of seed URLs, fetches pages, extracts links, and places them into a queue. Robots.txt rules and meta tags control which areas are visited and which are ignored. Modern crawlers handle JavaScript rendering, while simple crawlers only see the initial HTML and miss content loaded after the fact.
Pitfalls in SEO work
A faulty robots.txt accidentally blocks important pages, a missing sitemap makes content harder to discover. Crawl budget is limited, especially for large shops it matters that search engines do not waste resources on irrelevant filter URLs. Logfile analyses show which bots visit which sections and how often.
Context in marketing work
If you want your site to be visible in search engines, you should understand how crawlers work and which technical signals they evaluate. Structured data, clean internal linking, and fast response times make the bots' job easier. In B2B, sales teams use crawler based tools to build lists of potential customers from publicly available web data.