I'll Set Up Instant INN/OGRN Format Validation for Your Form

I take on the part of onboarding forms that most teams patch only after a bad tax number slips into their database: real-time validation of a counterparty's INN and OGRN numbers, checked the moment someone types them rather than after the form is submitted. The script knows the expected length before the person finishes typing — 10 digits for a legal entity, 12 for a sole proprietor, 13 or 15 for OGRN — and recalculates the checksum using the standard tax-authority formula as each digit lands. The moment the digits match, the field turns green; if something is off, it turns red with a short note explaining exactly what's wrong — a missing digit, an extra character, or a checksum that doesn't add up.

This is pure format validation, done without contacting any external registry or business database — I'm not building a lookup or a status check, just a fast, self-contained sanity check on the number itself. The logic runs in the browser for instant feedback, and I mirror the same check on the server before the record is saved, so a disabled script or a form submitted outside the usual flow still can't push a malformed number into your system. The submit button stays disabled until both checks — length and checksum — pass.

What's included in the setup:
— checksum calculation for both INN formats (10 and 12 digits) and for OGRN/OGRNIP, using the standard published algorithms;
— live inline highlighting and error text, no page reload;
— submit blocked while the number is invalid;
— matching server-side validation for direct form submissions;
— styling adapted to your existing form markup, no external libraries or third-party services.