# Premise key

A premise key is the digest of one building — country, postcode or town, folded street name and house number — that every spelling of the same address shares.

Date: 2026-09-16

A premise key is the digest of one building: the country, the postcode or the town where there is no postcode, the street name folded to its comparison form and the house number, hashed so that "12 High St", "12 High Street" and "12, HIGH STREET" all share one key.

## What Spaw answers

`premise_key` carries that digest in hex on every valid answer that names a street and a house number, and `null` where there is no building to key — a box, a street without a number, an address with neither postcode nor town. It is the same key the national registers are compiled under, the key an account's own delivery reports are filed under, and the key the suppression list holds, so a customer can join lookups, feedback and suppressions on one value, or deduplicate a list without re-implementing the folding.

## What it is a fact about

A place, and only a place: the key is derived from the address parts and nothing else, carries no name, and is the same for everyone who writes that address. It changes only when the folding rules change, which the `address-rules` version in `sources` records.

Reference: https://spaw.co/glossary/premise-key