Hreflang: Getting Multi-Language Pages Mapped Correctly

Hreflang tells search engines that 2 or more URLs are the same content for different languages or regions, so the right version surfaces for the right searcher. It is the most error-prone markup in technical SEO, because it is the only markup that requires every page in a cluster to agree with every other page. The rules are unforgiving in a specific way. Each page must reference itself. Every page it names must name it back. Language and region codes must be valid ISO values, where en-GB is correct and en-UK is a common invalid guess. URLs must be absolute. If one page in a 12-language cluster omits its return link, search engines can discard the mapping for the whole cluster rather than for the single broken edge. Hreflang also has to agree with your canonicals. A page whose hreflang names a URL that canonicalizes elsewhere sends 2 conflicting instructions, and the engine resolves the conflict by trusting neither. The checks below verify the structure declared on the page, then fetch each alternate to confirm it responds, stays indexable, and canonicalizes to itself. Structure and target health are separate problems: a cluster can be perfectly formed and still point at 3 pages that no longer exist.