How an address is written in United Kingdom

The postal format table for United Kingdom — the order the lines go in, the parts its operator requires, what it calls them, and the words it prints on a box — and, separately, what this server actually holds for United Kingdom, so the page never implies a check it cannot run.

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Response

Look up any address to see the full API response, straight from the live service. The country decides which format it is read against.

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The order the lines go in

The parts are named rather than filled in: Spaw does not know an address in United Kingdom and will not invent one. This block is produced by the same function that rewrites a real address, so the line order, the capitals United Kingdom asks for and any text its operator prints on every envelope are the checker's own behaviour rather than a second description of it.

Organisation
12 Street name
Flat or unit
POST TOWN
POSTAL CODE

No recipient line: nothing in the response is about a person, so the name the envelope carries is not part of what is checked.

field	called here	required	capitals
organization	Organisation	optional	—
addressLine1	Street name	required	—
addressLine2	Flat or unit	optional	—
locality	Post town	required	yes
postalCode	Postal code	required	yes

No house-number rule is carried for United Kingdom, so the international default is used: the house number comes before the street name. The postal code is written after the town.

The postal code

United Kingdom postal codes are checked against the pattern below rather than a description of it, because the shape is too particular to summarise without losing a case.

pattern GIR ?0AA|(?:(?:AB|AL|B|BA|BB|BD|BF|BH|BL|BN|BR|BS|BT|BX|CA|CB|CF|CH|CM|CO|CR|CT|CV|CW|DA|DD|DE|DG|DH|DL|DN|DT|DY|E|EC|EH|EN|EX|FK|FY|G|GL|GY|GU|HA|HD|HG|HP|HR|HS|HU|HX|IG|IM|IP|IV|JE|KA|KT|KW|KY|L|LA|LD|LE|LL|LN|LS|LU|M|ME|MK|ML|N|NE|NG|NN|NP|NR|NW|OL|OX|PA|PE|PH|PL|PO|PR|RG|RH|RM|S|SA|SE|SG|SK|SL|SM|SN|SO|SP|SR|SS|ST|SW|SY|TA|TD|TF|TN|TQ|TR|TS|TW|UB|W|WA|WC|WD|WF|WN|WR|WS|WV|YO|ZE)(?:\d[\dA-Z]? ?\d[ABD-HJLN-UW-Z]{2}))|BFPO ?\d{1,4}

A national directory is installed for United Kingdom, so a postal code here is not only checked for shape but looked up: 2,665,797 codes from ons-postcode-directory, version 2026-08, of which 1,760,216 are live and 905,581 have been retired. A retired code is usually a real address with an out-of-date code rather than a typo, so it is scored rather than refused.

BT codes are excluded from that directory: reusing them needs a separate licence, so an address carrying one is answered as though no directory were installed rather than as though the code did not exist.

What United Kingdom calls an address that is not a front door

The words below are United Kingdom's own, taken from its postal operator's addressing guide, and they are the words the checker reads. Because they are carried, an address here with none of them answers street.

address_type	written as
private_mailbox Private mailbox at a mail-receiving agency	PMB
po_box Post-office box	PO BOX, P O BOX
general_delivery Held at the counter for collection	POSTE RESTANTE
military Military and diplomatic mail	BFPO

What can be checked for a United Kingdom address

Read from the datasets this server holds right now, not written into the page. For most countries the answer is the written form and the postcode shape and nothing beyond them — in particular not the row people assume is always there. An address can be perfectly formed and still not exist, and where no register is installed nothing here will pretend to know which.

check	for GB	what the answer means
Written form	yes	The address is split into United Kingdom's own parts and rewritten in the order above. A missing required part is named in one typed reason rather than a general failure.
postal code pattern	yes	Checked against the pattern the table carries for United Kingdom. A value that does not match answers invalid_postal_code.
postal code exists	yes	2,665,797 codes from ons-postcode-directory, live and terminated ones apart, so a retired code reads as retired rather than as a typo.
Kind of delivery point	yes	United Kingdom's own box naming is carried, so an address with no marker answers street rather than unknown.
Street exists	yes	886,152 streets from os-open-names, keyed by postcode district. match_level answers street on a hit.
Building exists	no	os-open-names lists streets, not buildings, so exists answers null here: not evaluated, never no. A street can be confirmed; a building cannot.
Companies at the address	yes	An open company register is installed for this country, so the number of companies giving the address as their registered office is counted, and a published threshold marks it as a mail drop.
Known mailbox branch	no	No operator branch list covers United Kingdom, so is_mail_drop is never set from one here.
Post actually arrives	no	Not from this page, and not from open data in any country: whether post is delivered, and the vacant, residential and agency flags that go with it, are the postal service's own licensed product. Those fields answer deliverability_checked: false rather than a guess.

Null means not evaluated, never no. How to read an address-existence answer sets out what a premise, street or postcode match proves, and what absence proves.

Other countries

address-formats 2026-09-05 · address-rules 2026-09-17 · os-open-names 2026-09-17 · ons-postcode-directory 2026-08 · company-registers 2026-09-01 · checked 2026-09-18

Wrong result, or is it about you? If this tool said something you think is wrong, tell us and a person reads it. If Spaw is holding data about you and you never signed up here — a customer may have had your address verified, or reported that a message to it bounced — erase it yourself, confirmed by mail to that address and with no account needed.

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