Web Crawler

A web crawler (also called a spider or bot) is an automated program that systematically browses the web by following links from page to page, downloading and indexing content as it goes. Search engines use crawlers to discover and index pages; data engineers use them to collect specific data at scale.

A crawler starts with seed URLs, downloads each page, extracts links, and adds new URLs to a queue that repeats until exhausted or a limit is reached. Unlike scraping a single page, crawling is about discovery and traversal at scale - combining a crawler with a parser creates a complete data collection pipeline.

Crawlers must handle rate limiting, session management, JavaScript-rendered pages, and anti-bot defenses. This ongoing maintenance cost is one of the primary reasons developers prefer data APIs - a stable API endpoint eliminates the need to crawl and re-parse websites every time the source changes.