HTML: Marking Duplicate Content

Canonical Tags

Marks duplicate content and refers to the URL that search engine crawlers should consider for indexing.

001  <head>
002    <link rel="canonical" href="https://canonical-url" />
003  </head>

It's also adviced for canonical URLs to refer to themselves as canonical to prevent crawlers from indexing URLs with parameters (especially with dynamic websites).

Alternate Language Content

These tags should be on all pages for all languages. Works just as well when alternative language versions are on another subdomain

001  <head>
002    <link rel="alternate" hreflang="en" href="" />
003    <link rel="alternate" hreflang="jp" href="" />
004    <link rel="alternate" hreflang="fr" href="" />
005  </head>