# Duplicate content

Canonical HTML: /atlas/duplicate-content
Atlas version: atlas-2026-07-28-v1
Category: Quality, provenance, and observability

## Definition

Duplicate content exposes the same or nearly the same material at more than one URL.

## How it works

Crawlers cluster similar representations and choose a canonical using redirects, link signals, sitemap entries, declarations, and content comparison.

## How to validate it

Inventory normalized hashes by URL, identify intended variants, and make canonical and internal-link signals consistent.

## Common failure

Parameter combinations and printer views can multiply one article into thousands of crawlable addresses.

## Related topics

- [Canonical links](/atlas/canonical-links)
- [Crawl traps](/atlas/crawl-traps)