Vat ID validator (EU and non-EU countries, with checksums)

Validate VAT numbers for European Union countries (and several other countries), with checksum verification.

Many libraries only check if a VAT number looks right (regex). vat_id_validator checks if it is right.

It verifies the checksum of the VAT number using country-specific algorithms (Luhn, Modulo 97, weighted sums, etc.). This means you can catch typos, transposed digits, and fake numbers instantly, without making a single network request to flaky government APIs like VIES.

Key Benefits

⚡ Instant & Offline: Zero network latency. No VIES downtime. Works everywhere.
🧮 Mathematical Verification: Catches invalid numbers that regex would pass (e.g., typos).
🛡️ Type-Safe Rust: Built for speed and reliability.
🌍 Multi-Country: Supports 30+ countries including EU, UK, Norway, Switzerland, Serbia, Russia, and Brazil.

🚀 Key Features

1. Explicit Country Validation

Don't guess! If you know the country, validate strictly against it.

// O(1) lookup - 2.3x faster than standard check!
let result = check_vat_by_country("GB999000005", "GB");

2. Serde Support

Enable the serde feature to serialize results straight to JSON.

{
  "value": "GB999000005",
  "is_valid": true,
  "is_valid_format": true,
  "is_supported_country": true,
  "country_name": "United Kingdom"
}

3. Country Identifier (GeoGuesser Mode)

Got a number but don't know where it's from?

use vat_id_validator::identify_country;

// Returns valid results for ALL matching countries
let matches = identify_country("999000005"); 

// Matches:
// - United Kingdom (it tries adding "GB" automatically!)
// - Any other country where "999000005" is valid

## Installation

Add this to your `Cargo.toml`:

```toml
[dependencies]
vat_id_validator = { version = "0.2.0", features = ["serde"] }

Usage

use vat_id_validator::check_vat;

fn main() {
    // Valid UK VAT number
    assert!(check_vat("GB999000005").is_valid);

    // Invalid format
    assert!(!check_vat("GB123").is_valid);

    // Valid format but invalid checksum
    assert!(!check_vat("GB999999974").is_valid);
}

🏎️ Benchmarks

We take "instant" seriously.

Operation	Time
`check_vat` (heuristic)	~1.06 µs
`check_vat_by_country` (direct)	~460 ns

Measured on M-series Mac. Your mileage may vary, but it will be fast.

Supported Countries

Andorra (AD)
Austria (AT)
Belgium (BE)
Brazil (BR)
Bulgaria (BG)
Croatia (HR)
Cyprus (CY)
Czech Republic (CZ)
Denmark (DK)
Estonia (EE)
Finland (FI)
France (FR)
Germany (DE)
Greece (GR)
Hungary (HU)
Ireland (IE)
Italy (IT)
Latvia (LV)
Lithuania (LT)
Luxembourg (LU)
Malta (MT)
Netherlands (NL)
Norway (NO)
Poland (PL)
Portugal (PT)
Romania (RO)
Russia (RU)
Serbia (RS)
Slovakia (SK)
Slovenia (SI)
Spain (ES)
Sweden (SE)
Switzerland (CH)
United Kingdom (GB)

License

MIT / Apache-2.0

vat_id_validator 0.2.0