STATION 03 · CHECKSUMS RUN FOR REAL

Validation & formatting bench

Paste a number; the bench parses it or tells you exactly why not. Failures are loud and specific — a validator that waves bad data through is worse than none.

What "valid" means here — and what it does not

A passing checksum proves the digits are internally consistent: the Luhn digit matches, the IBAN mod-97 remainder is 1, the phone number obeys NANP rules. It does not prove a card, account, or subscriber exists — no bench can know that, and any tool claiming otherwise is guessing. The phone bench also flags the fictional 555-01XX range when it sees it, so test data never masquerades as a real contact in your pipeline.