Quick answer
An invalid hreflang annotation has a language value or URL that does not meet the format NOTABIS can validate. The current check accepts x-default, two or three lowercase language letters, optional region forms, and an absolute resolved URL. It does not prove that alternate pages exist, link back, or are the right translations, so review the full international setup before changing a valid exception.
What the issue means
Hreflang annotations connect alternate versions of a page for different languages or regions. They are commonly declared as <link rel="alternate" hreflang="en-gb" href="https://example.com/uk/page">. Typos, malformed region casing, empty values, or unusable URLs can make the relationship unreliable.
Why it matters for SEO
Correct alternate annotations can help search systems choose a suitable regional or language URL when several versions exist. They are hints about equivalent pages, not translation quality checks or ranking guarantees. A malformed annotation can be ignored, while changing a valid language strategy without checking all alternates can create a different problem.
How NOTABIS detects it
NOTABIS inspects link[rel="alternate"][hreflang] elements. It accepts x-default, a two or three lowercase letter language code, and an optional region written with the implementation's supported casing; it also requires the href to resolve to an absolute URL. Invalid annotations are counted and shown with their language, raw URL, resolved URL, and validity state.
The rule does not validate ISO vocabularies beyond that format, request each target, check reciprocal annotations, compare content languages, or decide whether a region is commercially correct.
How to check it yourself
- List every alternate annotation in the HTML head.
- Check language and region values against your intended locale plan.
- Resolve each URL and request it as a normal user.
- Confirm that alternates describe the same page purpose and that each version points back where your strategy requires it.
- Check XML sitemap or HTTP-header annotations if you use those instead of, or in addition to, HTML links.
How to fix it
Generate annotations from one locale mapping, use consistent language and region values, and emit absolute URLs that resolve to the intended alternate pages. Remove stale locales, correct casing and spelling, and test the complete set on every template. Re-run the audit, then validate the international targeting in search documentation and your own regional results.
When this is intentional or does not need fixing
A monolingual site may have no hreflang annotations. A site can also intentionally use only x-default or a language-only target. The finding concerns an annotation that is present but malformed; do not add alternate pages solely to clear a warning.
Related issues
Read crawl coverage and audit limitations, canonical tags, and duplicate URLs. Google’s localized-versions guidance covers the broader language and regional relationship that this syntax check cannot prove. Review when an audit finding does not need fixing when the locale strategy is deliberate.
Run a NOTABIS audit
Run a NOTABIS SEO audit to list invalid hreflang annotations measured in your page HTML, then verify their targets and relationships manually.