What causes duplicate content problems on websites?

Duplicate content problems usually come from technical URL variations or the same text being published in more than one place.

Common causes include:

• URL parameters for tracking, sorting, or filtering, which can create multiple URLs for the same page content.
• HTTP vs. HTTPS versions of a site, or www vs. non-www versions, if both are accessible.
• Trailing slash differences or other small URL changes that point to the same content.
• Faceted navigation and filter pages on e-commerce sites, which can generate many near-identical pages.
• Pagination across articles or product listings, where each page has very similar content.
• Printer-friendly, mobile, or localized versions of pages that are too similar to the main page.
• Content syndication or scraping, where the same text is republished on another site.
• CMS or server misconfiguration, including missing or incorrect canonical tags, session IDs, or archive pages.

In short, duplicate content is usually caused by multiple URLs serving the same or very similar content, whether intentionally or accidentally.