bank-lint

Validate bank and account details offline — no API calls, no dependencies.

Supports IBAN (ISO 7064 mod-97, 89 countries) and US ABA routing numbers. UK sort codes are coming in a later release.

Part of a dual-language project: the same validation logic, verified against the same test vectors, is also available for JavaScript/TypeScript as bank-lint on npm.

Install

pip install bank-lint

Usage

from bank_lint import validate_iban, validate_us_routing

validate_iban("GB82 WEST 1234 5698 7654 32")
# ValidationResult(valid=True, value='GB82WEST12345698765432', error=None)

validate_us_routing("021000021")
# ValidationResult(valid=True, value='021000021', error=None)

Spaces and lower-case are handled for you; value is the normalised input.

API

validate_iban(value: str) -> ValidationResult

ISO 7064 mod-97 checksum plus per-country length.

validate_us_routing(value: str) -> ValidationResult

9-digit ABA routing number: prefix range + weighted checksum. Spaces and hyphens are stripped.

ValidationResult is a frozen dataclass:

valid: bool
value: str                    # normalised (spaces/hyphens removed)
error: str | None             # None when valid

error is one of:

• "INVALID_FORMAT" — pattern or ABA prefix fails
• "INVALID_LENGTH" — wrong length
• "INVALID_CHECKSUM" — fails the checksum
• "UNSUPPORTED_COUNTRY" — IBAN country code not in the registry

Scope

bank-lint checks the structural validity of a bank identifier — format, length, and checksum. It does not:

• confirm the account actually exists or is open,
• do name matching or Confirmation of Payee,
• look up bank or branch details.

Country IBAN lengths are sourced from the official SWIFT IBAN Registry.

License

MIT