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

PolyForm Noncommercial 1.0.0. Personal, research, and nonprofit use is allowed. Commercial use needs a separate license from the author.