Why this tool is useful
Use HTML Language Tag Checker when you need to inspect HTML lang and hreflang values for duplicates, missing declarations and malformed BCP 47 structure. The result is immediate and easy to verify before you reuse it.
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HTML Language Tag Checker
inspect HTML lang and hreflang values for duplicates, missing declarations and malformed BCP 47 structure.
Ready. Your working data stays in this browser.
How it works
Enter the values requested by HTML Language Tag Checker. The browser validates the input, performs the calculation locally and produces a copyable result with clear errors.
Practical example
A practical use is to run HTML Language Tag Checker on a small sample first, confirm the output, and then process the complete value or list.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.