How to Validate Spanish NIF, NIE, CIF and IBAN in Python

If you've ever built a form or backend system for the Spanish market, you've likely had to validate fiscal identifiers like NIF, NIE, CIF or IBAN. Each one has its own algorithm, edge cases, and validation rules — and implementing them correctly from scratch is surprisingly tricky. In this article, I'll show you how to validate all four identifier types with a single API call using Python, without having to implement or maintain the validation algorithms yourself. The Problem with DIY Validation Spanish fiscal identifiers are more complex than they look: NIF: 8 digits + 1 letter, validated with a modulo-23 algorithm NIE: Starts with X, Y or Z, then follows the NIF algorithm with substitution CIF: Letter + 7 digits + control character (can be a letter or digit depending on the entity type) IBAN: ES + 2 check digits + 20-digit BBAN, validated with MOD-97 Most implementations online have subtle bugs — incorrect CIF letter validation, missing NIE edge cases, or IBAN check digit errors. Get