About this tool
Customs paperwork is full of codes and abbreviations. A document code such as N935, a procedure code such as 4000 or an acronym such as MRN can stop you mid-declaration. This tool explains them. Say what kind of thing you saw, type it, and you see what it is, where you use it, an example and the source.
New staff, drivers, traders reading an error message and experienced declarants checking a code use it. It reads CDUK's own glossary, the CDS code lists on GOV.UK and the UK Trade Tariff. Search forgives typos, spacing and aliases. When a string has more than one meaning, every meaning is shown, labelled by type.
It explains terms and codes. It does not tell you which code to use on your declaration, which depends on your goods and the transaction.
How this was worked out
What the tool does with your answers, in order.
Say what you are looking up: a document code, a procedure code, an additional procedure code, a term or acronym, or “I’m not sure”.
Type the code, data element, acronym or phrase, or pick a popular one; matches appear as you type.
The tool searches an index held in your browser and tolerates typos, spacing and aliases.
If a string has several meanings, each is shown with its own type chip.
Each entry gives what it is, its category, jurisdiction and system, where you use it, an example and related terms.
Open the source link and note the date shown, because code lists change.
Worked example: Searching N935
- SearchN935
- One entry returneddocument code, Commercial invoice
- Jurisdiction and systemUnited Kingdom, CDS
- Where usedCDS import declaration, data element 2/3
- ExampleN935 · INV-2026-0412 · status AE
- Source and date are shown with the entry
Illustrative example. Check the source and date shown with each entry before you rely on it.
Your questions, answered.
Short answers about the Customs Acronym & Code Explorer.
What does N935 mean on a customs declaration?
N935 is a CDS document code for a commercial invoice, the invoice on which the declared customs value is based. It is entered in the documents data element of a CDS declaration, with the invoice reference and a status code. Search N935 in the tool to see the entry, the example and the source list.
What is an MRN?
MRN stands for Movement Reference Number. It is a unique reference given to a customs declaration or movement by the customs system that accepted it. You quote it on a GMR, on a transit accompanying document and in amendments. Search MRN to see related terms such as NCTS and the office of departure.
What is the difference between a procedure code and an additional procedure code?
A procedure code on a CDS declaration says what you are doing with the goods, for example 4000 for free circulation, and a previous procedure where relevant. Additional procedure codes add detail, such as C07 for a particular relief. Together they describe the customs treatment. Search either to see its definition and source.
Why does a code show more than one meaning?
Some strings are used in more than one list. Codes such as C21 and 000 can mean different things as a declaration type, a procedure code or an additional code. The tool shows every meaning with its type chip rather than guessing, so you can pick the one that matches where you saw it.
What are CDS data elements?
Data elements are the numbered boxes of information on a customs declaration, written as DE followed by a class and number, such as DE 2/3 for documents and references. Searching 2/3, DE 2/3 or de 2 3 finds the same entry. The tool explains what each element holds and where it is used.
Where do the definitions come from?
From a glossary CDUK authors and reviews, from the CDS code lists and tariff guidance on GOV.UK, and from the UK Trade Tariff for certificates, additional codes and footnotes. NCTS, ICS2, GVMS and ELO terms are sourced to each authority. Every entry shows its jurisdiction, source and the date it was reviewed.
Can I rely on a definition when completing a declaration?
Use it to understand a code, then check the official source before you file. Code lists change, and the right code depends on your goods and transaction. Every entry links to its source and shows its review date. Customs authorities decide what applies to your declaration.
What does this tool not cover?
It does not tell you which code to use, classify goods or check a declaration. It covers customs terms, CDS codes, tariff terms and related acronyms, not every code in every country. If your term is missing, use Suggest this term and it goes to our content owner.
Data sources
- CDS code lists (UK Trade Tariff volume 3 for CDS, GOV.UK) United Kingdom · Monthly check
- UK Trade Tariff: certificates, additional codes, footnotes United Kingdom · Daily
- CDUK customs glossary (authored, each entry sourced and dated) United Kingdom · On regulatory change
United Kingdom and European Union · data checked 3 Oct 2026. UK government data is reused under the Open Government Licence v3.0.
Guidance only — not adviceWhat this tool is, and is not
This tool gives general guidance and indicative figures based on the information you enter and on official data available at the date shown. It is not legal, tax, customs or financial advice, it is not a ruling or a decision by any customs authority, and it does not recommend any course of action, guarantee, amount, route, supplier or service.
Customs authorities decide the classification, value, origin, charges and guarantee amounts that apply. You remain solely responsible for your declarations, guarantees, shipments and transactions, and for checking every figure against HMRC’s published guidance and the official sources before you rely on it or act on it.
Rates, rules and data can change without notice, and the results may be incomplete or inaccurate. To the fullest extent permitted by law, Customs Declarations UK accepts no liability for any loss, cost, penalty, delay or damage arising from the use of, or reliance on, this tool or its results.
