Websites deploy a layered stack of anti-scraping measures at different levels of sophistication. Network-layer defences include IP rate limiting, IP reputation blocklists, and geographic IP filtering. Application-layer defences include JavaScript challenges, CAPTCHAs, honeypot fields, and dynamic HTML that changes selector paths. Browser-layer defences use fingerprinting to detect non-standard clients.
Legal measures — Terms of Service restrictions, DMCA notices, and cease-and-desist letters — complement technical defences. These are particularly relevant for large-scale commercial scraping operations targeting sensitive data.
Effective anti-scraping systems use a defence-in-depth approach: no single measure is impenetrable, but stacking multiple layers raises the cost of bypassing them enough to deter most scrapers. Professional scraping APIs like AlterLab are specifically engineered to navigate this stack, maintaining up-to-date compatibility techniques as protection vendors update their models.