Check the control letter of a Spanish DNI or NIE locally in your browser - with no upload, even offline.
Running locally on your device ...
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
The DNI (Documento Nacional de Identidad, 8 digits + control letter) identifies Spanish nationals; the NIE (Numero de Identidad de Extranjero, a leading X/Y/Z + 7 digits + control letter) identifies foreign residents. Both share the same official algorithm: the 8-digit number modulo 23, the remainder maps to a letter via a fixed table - the letters I, N, O and U deliberately never appear in it (risk of confusion with 1, Ñ, 0 and the letter N).
For a NIE, the leading letter is replaced by a digit before the calculation (X becomes 0, Y becomes 1, Z becomes 2), and the resulting 8-digit number is treated exactly like a DNI. This tool auto-detects from the first character whether a DNI or a NIE number was entered. Spaces and dashes in the input do not matter.
The whole calculation runs entirely locally in your browser in pure JavaScript - the number is not uploaded, not stored, and no foreign library is loaded from a CDN. You can download the result as a JSON file or read it directly.
| Input formats | Text input |
|---|---|
| Output format | JSON |
| Batch processing | No |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
Limitations: This tool performs only a mathematical checksum/format check. It is not an official identity, existence, or registry verification and not a request to any authority. Any additional information derived from the number's structure is based solely on the publicly documented encoding logic of the issuing authority.
No. The check runs entirely locally in your browser; the number never leaves your device and is not stored.
No. The tool only checks the mathematical control letter and the format - not a lookup against an official registry.
To avoid confusion: I with 1, O with 0, and because of the Spanish letter Ñ, N is also skipped. The official table deliberately leaves these four out.
By the first character: input starting with a digit is checked as a DNI; input starting with X, Y or Z is checked as a NIE.