A web crawler, also known as a spider, is a software program that systematically browses the internet to index and collect information from websites. Here’s how a web crawler works:
- Seed URLs: The web crawler begins with a set of seed URLs, which are typically provided by the search engine or determined by the crawler itself.
- Crawling: The web crawler follows each URL to the website and begins to crawl through the website’s pages, starting with the homepage.
- Indexing: As the crawler navigates through the website, it collects and indexes the content it finds, such as text, images, and metadata.
- Link analysis: The crawler also analyzes the links on the website to determine which pages to crawl next. It follows both internal links within the website and external links to other websites.
- Recursion: The crawler continues this process, recursively following links and collecting information until it has crawled all the relevant pages on the website.
- Storing: The information collected by the crawler is stored in a database or index, which can be used by search engines to provide relevant results to users.
Some additional points to keep in mind:
- Crawlers typically follow a set of rules, such as the robots.txt file, which specifies which pages the crawler can and cannot access.
- Crawlers may prioritize certain pages based on factors such as page authority and freshness.
- Crawlers may also use various techniques to handle dynamic content, such as JavaScript and AJAX, in order to properly index the content.
In summary, a web crawler is a software program that systematically browses the internet to collect and index information from websites. It follows links and recursively crawls through the website, storing the collected information in a database or index that can be used by search engines.