A crawler — also called a bot — is an automated software program that constantly roams the internet, reading websites, following links, and gathering information for search engines. Think of it as a robot that systematically visits web pages the way a human would, but at massive scale and speed.
Here's how it works in practice. You type "best laptop brands in Bangladesh" into Google. Ever wonder how Google instantly pulls up thousands of relevant results? That's crawlers at work. Programs like Googlebot continuously scan the web, analyze what's on each page, and store that information in Google's index. When you search, Google simply retrieves the most relevant pages from its pre-built database.
Crawlers are essential for making the internet searchable. When you launch a new website, Google's bot eventually discovers it, crawls through your pages, and adds them to search results. That's how new content becomes discoverable. But not all bots are good. Some malicious bots scrape content without permission, send spam, or overload servers with requests. That's why website owners often use tools like robots.txt to control which bots can access their site.