Subdomain (International)

A subdomain structure hosts each language or country version on its own hostname under your domain: fr.example.com, de.example.com, uk.example.com. The stakes: you're betting that whatever forced you onto separate hosts is worth links and authority consolidating less cleanly than they would in folders on one domain.

What it looks like in the wild

Recognizable patterns:

• fr.wikipedia.org, de.wikipedia.org — the canonical example of subdomains at massive scale, one per language
• es.example.com — Spanish-language version on its own host
• uk.example.com — a market subdomain (note: the hostname label uk is branding; in hreflang the region code must be GB)

Technically each subdomain is a separate host with its own DNS record, and can have its own server, stack, and deployment pipeline. That independence is the whole reason to choose it — and the source of the SEO argument against it.

The "separate site" question

Google's official line has been consistent for years: subdomains and subdirectories are both fine, use what works. Practitioners keep finding cases where content moved from a subdomain into a subfolder gained visibility, and cases where it made no difference. The honest reading: Google treats subdomains approximately as separate sites for some signals — link equity and quality evaluation don't flow across hosts as freely as within one host — but it's not a binary wall, and results vary by site. The site's own subdomain vs subdirectory study digs into real performance data, and the subdomain vs subdirectory comparison walks the argument end to end.

When a subdomain actually makes sense

Don't frame this as "which is better in a vacuum" — frame it as "what constraint are you under." That's the honest decision:

If none of the "good" rows describe you, default to a subdirectory structure and move on.

Subdomains and hreflang

Hreflang works identically across hosts — annotations can point from fr.example.com to de.example.com without issue, since hreflang is a clustering signal, not a directive tied to one host. The rules don't change: full absolute URLs, reciprocal return tags, and one implementation method only. Because each subdomain is often deployed independently, subdomain sites are especially prone to one host emitting hreflang via HTTP headers while another uses head tags — that mix silently breaks the cluster. The hreflang implementation guide has the full method rundown.

How to check it

1. List every live language subdomain from DNS or your CDN config — shadow subdomains (old www2., staging hosts) that still resolve are duplicate-content generators.
2. Crawl each subdomain in Screaming Frog with crawl scope set to include subdomains, then open the Hreflang tab and check "Missing Return Links" across hosts — cross-host reciprocity is where subdomain setups break first.
3. Compare headers per host: curl -sI https://fr.example.com/ vs curl -sI https://de.example.com/. Different stacks drift: one host redirects HTTP→HTTPS, another doesn't; one emits a Link: hreflang header, another has head tags.
4. Verify each subdomain in Search Console separately (or verify at the domain level) — a subdomain that nobody added to GSC is a market flying blind.

Common mistakes

• Choosing subdomains for "cleanliness" with no operational reason. If one team runs one CMS, you took the authority split and got nothing back. Fix: migrate to folders before the content footprint grows.
• Country-code hostnames leaking into hreflang. uk.example.com is fine as a hostname, but hreflang="en-uk" is invalid — the ISO region is GB. Fix: decouple branding labels from annotation values.
• Wildcard DNS. *.example.com resolving means anything.example.com serves your homepage — infinite duplicate hosts. Fix: explicit DNS records per subdomain, 404 or redirect the rest.
• Inconsistent canonical domains per host. fr. canonicalizes with a trailing slash, de. without. Each inconsistency doubles hreflang permutations. Fix: enforce one URL normalization policy across all hosts at the edge.
• Forgetting subdomains in analytics and monitoring. Rank tracking, log analysis, and uptime checks configured for the root only. Fix: treat every language host as a first-class property everywhere.

FAQ

Is a subdomain a separate website to Google?

Partially, and it's contested. Google says both structures work; observed migrations sometimes show gains moving subdomain content into folders. Treat the safe assumption as: authority consolidates less reliably across hosts than within one.

Can hreflang connect a subdomain to a subdirectory site?

Yes — hreflang can cluster URLs across any hosts and even different domains, as long as annotations are absolute and reciprocal. It's ugly to maintain, but valid.

Do I need separate Search Console properties for each subdomain?

A domain-level property covers them all in one view. Add per-subdomain URL-prefix properties too — that's how you get clean per-market performance and indexation data.

We're on subdomains and it's working. Should we migrate to folders anyway?

No. Migrations have real costs and "working" is evidence. Migrate when subdomains are demonstrably underperforming, when infrastructure consolidates anyway, or when maintenance pain exceeds the switching cost — not because a blog post said folders are better.