Duplicate Content

Definition

Duplicate content occurs when identical or substantially similar content exists at multiple URLs — either within the same website (internal duplication) or across different websites (external duplication). It's one of the most common SEO issues. Internal causes include: www vs. non-www versions, HTTP vs. HTTPS, trailing slash variations, URL parameters (filtering, sorting, session IDs), print-friendly pages, and paginated content. External causes include: content syndication, scraped content, and boilerplate legal pages. While Google doesn't penalize duplicate content with a formal penalty, it does: choose only one version to index (potentially the wrong one), split ranking signals between duplicates, and waste crawl budget on redundant pages. Fixes include: canonical tags (rel='canonical') to specify the preferred version, 301 redirects for retired URLs, robots.txt or noindex for non-canonical versions, and using hreflang for international content variants.