Hreflang checker — tags & return links, tested live

What the hreflang checker verifies

• Language & region codes — ISO 639-1 language (plus optional ISO 3166-1 region or script subtag), hyphens not underscores, and the classic en-UK mistake (the code for the United Kingdom is GB).
• Self-reference & x-default — the page must list itself in its own hreflang set, and Google recommends an x-default entry for the fallback version.
• Absolute URLs & duplicates — relative hreflang URLs are invalid, and one language must not point at two different URLs.
• Return links (reciprocity), tested live — every alternate is fetched and its own hreflang set is read to confirm it links back to the page you're checking. If page A references page B but B doesn't reference A, Google ignores the annotation entirely.

Why return links are the check that matters

Most hreflang audits stop at syntax — but the rule that actually breaks international SEO in practice is reciprocity. Google only honors hreflang annotations when every page in the cluster confirms them: your English page says "the French version is over there", and the French page must say the same about the English one. A redesign that drops the tags from one template, a locale added on one side only, or a trailing-slash difference between the declared URL and the real one is enough for the whole cluster to fall apart — with no error anywhere in Search Console, just the wrong language showing up in the wrong country. Because this tool fetches each alternate live, it catches exactly that class of silent breakage.

Common hreflang mistakes it catches

en_US with an underscore, en-UK instead of en-GB, a region code alone (fr the language ≠ FR the country), relative URLs, a missing self-reference, the same language declared twice with different URLs, alternates that redirect or 404, and hreflang tags on a noindex page. Each check explains the fix inline.

This check runs live and stores nothing. To monitor the hreflang clusters across your whole site on a schedule — and get an email when a return link disappears — try siteOS. Also useful: the meta tags checker for titles and canonicals across your sitemap, and the OG image checker for your share images.