FAQ

Short answers, each with the rule of SPEC.md that backs it.

Is 00000000T a valid DNI?

Yes. 00000000T has the right check letter, and no law forbids it, so it is valid by default, like the other well-known placeholders 00000001R, 99999999R and X0000000T. Some registries, such as ESNIC (the .es domain registry), filter them as known placeholder values, but being on that list doesn’t prove that a number was never assigned. If you want to refuse them too, pass rejectPlaceholders: true (an opt-in policy), and validate() reports the code PLACEHOLDER (POLICY-1).

import { isValidDni, validate } from "nif-dni-nie-cif-validation";

isValidDni("00000000T");                                   // true
isValidDni("00000000T", { rejectPlaceholders: true });     // false
validate("x-0000000-t", { rejectPlaceholders: true }).error?.code; // "PLACEHOLDER"

Are old CIFs still valid?

Yes. In 2008 Orden EHA/451/2008 replaced the name “CIF” with “NIF of a legal person or entity”, but the numbers didn’t change, and no organisation key has ever been removed (CIF-2). What the order did change is the 7 digits: they became random and no longer encode a province, so the library doesn’t check province codes (CIF-5).

One kind of old value fails by default: a CIF with the keys C, D, F, G, J, U or V and a letter as its control character. See the next question.

Why is G1234567D invalid?

Because the key G takes a digit. The AEAT’s technical note on the NIF gives a digit to the keys A B C D E F G H J U V and a letter to N P Q R S W (CIF-3). Many libraries, and version 1 of this one, accepted either for C, D, F, G, J, U and V, which has no official basis. The digit with the same value is valid:

import { isValidCif, validate } from "nif-dni-nie-cif-validation";

isValidCif("G1234567D");                            // false
validate("G1234567D").error?.expected;              // "4"
isValidCif("G12345674");                            // true
isValidCif("G1234567D", { cifControl: "lenient" }); // true: the version 1 behaviour

If your stored data has such numbers, pass { cifControl: "lenient" } while you clean it up. It only changes the keys C, D, F, G, J, U and V: A, B, E and H always take a digit, and N, P, Q, R, S and W a letter.

Is there an NIE that starts with T?

No. No official source defines a NIF or an NIE starting with T. NIEs start with X, Y or Z (NIE-1), and a value that starts with any character that no kind of NIF uses is rejected with the rule NIF-1:

import { validate } from "nif-dni-nie-cif-validation";

validate("T1234567A").error?.code; // "INVALID_FORMAT"
validate("T1234567A").error?.rule; // "NIF-1"

Must a CIF starting with 00 have a letter?

No. Some libraries require a letter control when the digits of a CIF start with 00. That rule traces back to an uncited table, and no official list has ever had a province code 00, so the library doesn’t apply it (see Explicitly NOT implemented). The control type depends on the key only:

import { isValidCif } from "nif-dni-nie-cif-validation";

isValidCif("B00123455"); // true: B takes a digit, whatever the digits

Does a valid VAT number mean it is registered in VIES?

No. isValidSpanishVat() checks the format: ES followed by a valid NIF (VAT-1). Whether the number is registered for intra-EU trade is a fact only the tax administration knows: query the European Commission’s VIES service for that. Likewise, a valid NIF is a well-formed number, not proof that it was ever issued to anyone: the AEAT has its own service to check the NIF of a third party.

import { isValidSpanishVat } from "nif-dni-nie-cif-validation";

isValidSpanishVat("ES12345678Z"); // true: the format is right
isValidSpanishVat("12345678Z");   // false: the ES prefix is required

Is the old 10-character NIE still valid?

Yes. NIEs issued before 2008 have an X, 8 digits and a letter, such as X01234567L. They stay valid, and their canonical form drops the zero after the X: X1234567L (NIE-3). validate() returns that form in normalized.

Why does isValidDni accept K, L and M?

Because K, L and M NIFs are issued to people who have no DNI, and they use the DNI’s check letter (KLM-1, KLM-2). isValidDni() has accepted them since version 1. To accept a DNI only, use validate(value, { types: ["DNI"] }):

import { isValidDni, validate } from "nif-dni-nie-cif-validation";

isValidDni("K1234567L");                                 // true
validate("K1234567L", { types: ["DNI"] }).error?.code;   // "UNSUPPORTED_TYPE"

Where does the DNI letter algorithm come from?

From the Ministerio del Interior, which publishes it, and the AEAT’s technical note on the NIF. It is not in any law: the law only says that a DNI ends with a check letter. How the control character works explains it step by step, with the source of every rule.