What Is Web Scraping? Data Extraction Explained
Web scraping is the automated extraction of data from websites. A scraper fetches HTML pages, parses the DOM, and extracts structured data — prices, job listings, research data, sports scores. Scraping powers search engines, price comparison sites, academic research, and business intelligence tools.
How Scrapers Work
Basic scraper: HTTP request → parse HTML with a library (Beautiful Soup, Cheerio, lxml) → extract elements by CSS selector or XPath → store data. For JavaScript-rendered pages, a headless browser (Puppeteer, Playwright) renders the full DOM before parsing. For large-scale scraping, tools like Scrapy manage request queues, politeness delays, and deduplication.
Robots.txt and Polite Scraping
robots.txt tells scrapers which paths are off-limits. Always check and respect robots.txt (though it is not legally enforceable). Polite scraping rules: identify yourself with a descriptive User-Agent containing a contact URL, add random delays between requests (1–5 seconds), don't hammer servers during peak hours, cache pages to avoid re-fetching, and don't use scraped data to compete directly with the source.
Legal Considerations
Scraping public data is generally lawful (hiQ v. LinkedIn, 2022 9th Circuit ruling). Scraping copyrighted content may infringe copyright. Scraping personal data in a GDPR jurisdiction requires a legal basis. Terms of Service violations are contractual, not criminal — but violating them may result in IP bans or legal action. Creating derivative products or selling scraped data has additional considerations.