TL;DR: Free China resident ID validator per GB 11643: checks division code, birthdate, gender digit, and the MOD 11-2 checksum locally. Format validation only — no online registry lookup.
This tool runs entirely in your browser. Open DevTools → Network panel and search your input — it appears in no request.
Usage Guide
A mistyped digit in a signup form, a valid sample needed for a test environment, dirty legacy data to scrub — "is this resident ID well-formed" is a frequent question. This tool validates the GB 11643 18-digit structure locally: 6-digit division code + 8-digit birthdate + 3-digit sequence (odd = male, even = female) + 1 MOD 11-2 check digit, with the exact failing part named. Format validation only; nothing is queried or stored.
1. The checksum in one paragraph
Each of the first 17 digits multiplies a fixed weight [7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2]; the sum mod 11 maps to the check character 1 0 X 9 8 7 6 5 4 3 2 — which is why a trailing X is perfectly normal (it encodes remainder 2, not "unknown"). Flip any digit and the check fails, which is what makes the scheme effective against typos.
2. What it deliberately does not do
It answers "is this number well-formed", never "does this number exist / belong to someone" — that requires the official registry, and any non-official site claiming online real-identity checks is suspect. Division validity is checked at province level only (county codes shift with administrative reorganization). For test fixtures use the companion generator in this suite: format-valid, sequence-randomized, mapping to no real person.