x-default

x-default is a special hreflang value that names the fallback page a search engine should show when no other language or regional version matches the user.

In a set of hreflang annotations, each version normally maps to a language and optional region, like en-us or fr-ca. The x-default value is the catch-all: it points to the page meant for any visitor whose language or country is not covered by your other versions. It is declared with the reserved value x-default in place of a language code.

<link rel="alternate" hreflang="en-us" href="https://example.com/us/" />
<link rel="alternate" hreflang="fr-fr" href="https://example.com/fr/" />
<link rel="alternate" hreflang="de-de" href="https://example.com/de/" />
<link rel="alternate" hreflang="x-default" href="https://example.com/" />

A good x-default target is usually a global homepage, a generic English page, or a country-and-language selector that lets visitors choose for themselves. The point is to give users who fall outside your targeted markets a sensible place to land instead of an arbitrary version. Imagine a site with US English, French, and German versions: a visitor browsing in Japanese matches none of them, so the x-default page is what gets served.

x-default is optional but strongly recommended. Without it, search engines pick a fallback on their own, which may not be the version you would choose. A frequent error is omitting x-default entirely, leaving unmatched users to chance. Another is pointing every page's x-default at a single homepage when a more specific fallback would serve better. Like all hreflang values, x-default should be declared consistently across the whole set and should return a self-referencing annotation where appropriate.

Related: Missing x-default, Where to declare hreflang, Hreflang best-practice scenarios, Language Targeting