Web Crawler
A web crawler systematically discovers and follows links across a site or the broader internet to build an index. Commonly known as a crawler bot or spider, this automated system maps the topology of the web by resolving DNS records, parsing HTML documents, and extracting href attributes to map out navigation paths. Search engines like Google and Bing rely on these systems to feed their global indexes.
While the terms are often used interchangeably in casual speech, a web crawler vs web scraper distinction is crucial in data engineering. A crawler focuses on discovery and link traversal, whereas a scraper targets specific pages to extract structured fields. A typical web crawler example involves crawling an entire e-commerce domain to collect a master list of product URLs, which are then passed to an extraction pipeline. Understanding how a web crawler works is foundational when building any data collection infrastructure, as discovering URLs is the necessary precursor to extracting data.
Key Specifications & Comparison
Understanding the technical boundaries between crawling and scraping determines your infrastructure choices.
| Feature / Operation | Web Crawler | Web Scraper |
|---|---|---|
| Primary Goal | URL discovery and site indexing. | Field extraction and structural parsing. |
| Logic | Follows href links recursively. |
Selects CSS classes or XPath nodes. |
| Data Output | Raw HTML or lists of URLs. | Structured JSON, CSV, or database records. |
| Tooling | Scrapy (Spiders), Apache Nutch. | Web Scraper API, Puppeteer. |
Related terms
Pagination (Web Scraping Pagination)
Learn what pagination means in web scraping, how numbered, next-link, and cursor patterns differ, and how to work through paged results without missing records.
Read more →XPath
Learn what XPath is, how it selects nodes by structure and content in HTML, and how it compares to CSS selectors for web scraping, with a syntax cheat sheet.
Read more →Public Data Scraping
Learn what public data scraping means, how hiQ v. LinkedIn shaped the legal picture, and why public access does not mean unrestricted use of the data.
Read more →Web Scraper API
Developer-friendly endpoints that return structured data in milliseconds.
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