Form GST ITC 1 standardises reconciliation of input tax credit claims, mismatches, duplicate claims and credit note adjustments. Form GST ITC 1 establishes a structured reporting mechanism (ITC 1A, ITC 1B, ITC 1C) for reconciling input tax credit claims by itemising matched and mismatched invoices, duplicate claims, and credit note adjustments; it quantifies differences between ITC claimed and output tax declared, prescribes that unmatched recipient additions remain pending until supplier pairing or supplier return filing, and generates mismatch, duplicate claim and e commerce reconciliation reports that identify amounts to be added to output tax liability.