15-character gstin, explained. state · pan · entity code · checksum.
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structure
gstin = state code (2) + PAN (10) + entity-within-state (1) + "Z" (1) + checksum (1).
the checksum uses a modulo-36 algorithm over base-36 digits. this tool validates format and checksum — not whether the entity is registered or active. for live lookup, use the GSTN portal.