The same content at several addresses.
WHERE IT COMES FROM
Both www and non-www resolving Both HTTP and HTTPS resolving Alias domains serving the same site Filter and sort parameters creating variations Printer-friendly versions Tag and category pages duplicating content
WHY IT MATTERS
Search engines must choose which version to show.
Ranking signals split between versions.
THE CANONICAL TAG
Tells search engines which version is authoritative.
SEO plugins handle it for most cases.
THE REDIRECT APPROACH
Better where possible. Redirect all versions to one.
FOR WWW AND NON-WWW
Choose one. Redirect the other permanently.
FOR HTTP AND HTTPS
Redirect all HTTP to HTTPS.
FOR PARAMETERS
Canonical tags pointing at the clean version.
FOR TAGS AND CATEGORIES
Consider whether they add value.
If a tag page has three posts and no description, it may be better not indexed.
WHAT TO CHECK
Search for a distinctive phrase from your site and see how many addresses appear.
