CDS and NCTS live behind the same Government Gateway session, but the payloads they accept are not the same shape. Teams building integration layers keep discovering this the hard way.
CDS payload essentials
A CDS declaration carries classification, valuation, origin evidence and the duty and VAT position. It represents a settled customs event. Every field maps to an obligation HMRC will audit against.
NCTS payload essentials
An NCTS declaration is built around a guarantee reference, a consignment structure and an itinerary of offices. It represents a suspended customs event. This technical comparison of NCTS and CDS walks through the operational implications.
Where integrations fail
Shared credentials trick teams into designing one connector for both. Amending a commodity code through the CDS endpoint does nothing to the NCTS record. A robust integration writes to both explicitly.
What to build for
Model each system as its own service. Reconcile at the consignment level using shared references, not shared assumptions.
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