null. Write your client so it tolerates missing keys.
Top-level fields
An empty array is a normal result, not an error. If the engine finds no match in a taxonomy it returns
[] with a 200, so check array length before indexing.Classification entries
RTICs, RSICs and RNAICs share a shape. Only Code is guaranteed.
SICs are different, because they are the statutory codes registered at Companies House rather than something the engine infers. They carry no score:
Similar companies
Every field here is always present.
The request takes no limit or paging parameters, so the number of companies returned is whatever the classification engine gives for that input.
Ordering and stability
Array order is whatever the classification engine returns, and we don’t guarantee it. Sort byScore or Similarity yourself if you need a ranking.
Treat scores as subject to change too, since the underlying models are retrained. If you persist results, store the Code values and the date you fetched them rather than assuming the same input always produces identical scores.