Number Validator Guides
How each number is built and how its check digits are calculated, with worked examples from the official sources.
Spanish DNI, NIE and NIF
How the control letter is calculated, NIE prefixes X, Y and Z, and company NIFs.
Read guide →Turkish Identity Number
The T.C. Kimlik No check digits, why the last digit is even, and what the number does not reveal.
Read guide →Russian INN and SNILS
Check digits of 10- and 12-digit ИНН and of the СНИЛС, with worked examples and the 2026 order.
Read guide →Brazilian CPF and CNPJ
Check digits of the CPF and CNPJ with worked examples, and what the alphanumeric CNPJ of July 2026 changes.
Read guide →IBAN Structure
Country formats from the SWIFT registry and the MOD 97 check digits, validated and calculated step by step.
Read guide →Italian Codice Fiscale
How the 16 characters are built, the control letter step by step, omocodia and the numeric code.
Read guide →Use the Number Validators
The guides explain the rules; the validators check numbers in your browser.
Frequently Asked Questions
Does a correct check digit mean the number exists?
No. It only shows that the number is well formed. Whether a number was really issued, and to whom, can be confirmed only by the authority that issues it.
Are the numbers I enter stored?
No. The validators run in your browser, and what you enter is not sent to LeedyBox or saved.