NPI validator
Check whether a 10-digit National Provider Identifier is structurally valid. Validation runs entirely in your browser using the NPI check-digit algorithm, so nothing is sent anywhere.
How NPI check-digit validation works
An NPI is a 10-digit number whose last digit is a Luhn check digit. To validate it, the first 9 digits are prefixed with 80840 (the ISO issuer identifier for US health applications), the Luhn algorithm is run over those 14 digits, and the result must match the 10th digit. A number that fails this test cannot be a real NPI. Passing it only proves the number is well-formed, though, not that it's actually assigned to anyone. To confirm a provider exists, look it up in the NPPES registry.