Private, browser-local utility
BCP 47 Language Tag Validator
Check language-tag well-formedness and show browser-runtime canonical form locally.
Your input and result stay in this browser tab. Nothing is uploaded, fetched, logged, or stored.
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Result
Validation model
The validator uses the browser’s Intl.getCanonicalLocales implementation for standards-aware well-formedness and canonicalization, plus bounded structural decomposition. Private-use-only tags and a pinned set of grandfathered preferred replacements are handled explicitly.
It does not download or claim complete current IANA Language Subtag Registry membership validation. A syntactically well-formed tag can contain subtags whose current registration status this tool does not verify. Limit: 255 characters.