Duplicate Content
Substantially similar content appearing on multiple URLs. Confuses search engines about which version to rank. Fix it with canonical tags, redirects, or by consolidating pages.
Why It Matters
Duplicate content doesn't trigger a "penalty" in the traditional sense - Google won't manually punish your site for it. But it does cause problems. When the same content exists at multiple URLs, Google has to choose which version to index and rank. It splits crawl budget, dilutes ranking signals, and often picks the wrong version.
Duplicate content is also far more common than most people realise. URL parameters, session IDs, print-friendly versions, HTTP vs HTTPS, trailing slashes - all of these can silently create duplicates.
In Practice
Audit your site for duplicates using Screaming Frog or Sitebulb. Look for pages with identical or near-identical content at different URLs.
Fix duplicates with the right tool: canonical tags for URL parameter variants, 301 redirects for old URLs that should point to new ones, and content consolidation for pages that genuinely compete with each other.
Set up proper URL standardisation from the start. Pick HTTPS, pick www or non-www, handle trailing slashes consistently, and redirect all variants to your canonical format.
Common Mistakes
Ignoring URL parameter duplicates. Using 302 redirects instead of 301s for permanently moved pages. Having both HTTP and HTTPS versions live without redirects. Creating separate pages for topics that should be consolidated.
Related Terms
Glossary
Canonical Tag
Tells search engines which version of a page is the original when duplicates exist.
Glossary
Redirect (301 vs 302)
301 is permanent (transfers ranking signals), 302 is temporary - use the right one.
Glossary
Keyword Cannibalisation
When multiple pages on your site compete for the same keyword, splitting authority.
Glossary
Crawl Budget
How many pages Google will crawl on your site in a given timeframe.
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