Attest.DataAnnotations 1.0.0

Attest

Validates national identification numbers, tax identification numbers, VAT codes and postal codes for 80+ countries.

Attest started as a fork of CountryValidator by Anghel Valentin, which has had no release since 1.1.3 and a number of open validation bugs. The country rules and coverage come from that project; see CHANGELOG.md for what has been fixed since, and NOTICE for attribution.

Install

Install-Package Attest
Install-Package Attest.DataAnnotations

Use

using Attest;

var validator = new CountryValidator();

ValidationResult result = validator.ValidateIndividualTaxCode("93051822361", Country.BE);
if (!result.IsValid)
{
    Console.WriteLine(result.ErrorMessage);
}

Asking by category

When you do not want to name a method — "is this any business identifier for this country?" — ask by kind:

using Attest;

var validator = new CountryValidator();

IdentifierResult result = validator.Validate(value, Country.BE, IdentifierKind.Business);

if (result.IsValid && !result.IsAmbiguous)
{
    // definitely a company number or a VAT number
}

IdentifierKind is a flags enum: PersonalId, PersonalTaxCode, CompanyNumber, Vat, PostalCode, plus the combinations Person, Business and Any (the default, which covers personal and business identifiers but not postal codes).

Two things the result tells you that a plain boolean cannot:

• IsAmbiguous — a few countries issue one number that serves as both a personal and a business identifier. Armenia (the 8 digit ՀՎՀՀ, whose digits carry no meaning by the State Revenue Committee's own account) and Nigeria are the two here, and in Russia a sole trader files VAT under his personal number, so that one number is both. There, a value asked about as a business identifier can be valid and indistinguishable at the same time, and the flag says so instead of guessing.
• Supports(country, kind) — whether the country has a rule for that kind at all. A kind with no rule reports every value invalid, which is not a verdict on the value. 33 of the 435 country/kind pairs in this library have no rule.

Matched lists every kind the value is valid as, and Details carries the individual ValidationResult for each kind that was evaluated.

Each country also has its own validator class in Attest.Countries, if you want to skip the dispatch:

using Attest.Countries;

bool valid = new BelgiumValidator().ValidateVAT("BE0428759497").IsValid;

Using Data Annotations

[HttpPost]
public IActionResult ValidateSSN([Required, SSNAttribute(Country.US)] string ssn)
{
    if (!ModelState.IsValid)
    {
        return BadRequest();
    }

    return Ok();
}

Supported Countries

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Contributing

CONTRIBUTING.md has the rules this project runs on — every one of them exists because a validator here was wrong for years without anyone noticing. The short version: cite a published source for any rule you change, compute your own test numbers rather than copying them, and never write a test that asserts behaviour you believe is wrong.

docs/adding-a-country.md walks through adding or fixing a country.

KNOWN-ISSUES.md is the backlog: weaknesses found and deliberately left alone, each with the reason. Most are one validator and its test file, which makes them the natural place to start.

Security reports go through SECURITY.md. Conduct: Contributor Covenant.

License

Apache License, Version 2.0 — see LICENSE.

Copyright 2020 Anghel Valentin (original work) Copyright 2026 Yehor Hrabovskyi (changes)

Special thanks

Python Stdnum