Postal address checker
Paste an address and see what kind of delivery point it names — an ordinary street address, a post-office box, a private mailbox at a mail-receiving agency, general delivery, a rural route, military mail, a parcel locker or a business-volume arrangement — whether its postcode exists in the national directory, and what the open registers say about the building. Every check runs against data on this server, so the address is not sent anywhere else.
Live demo
POST /demo/address · no key needed
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.
Three questions, answered separately
Most address tools answer one blurred question — "is this address good?" — and leave you guessing which part failed. This one keeps them apart, because the fixes are different.
Does it stand as written for its own country?
Each country has its own format: which lines are required, which side of the street name the house number goes on, what its postcode looks like and what it calls it. The address is split into that country's parts and rewritten the way its postal operator writes it. When something required is missing or malformed, the answer says which part, in one typed reason.
What kind of delivery point is it?
A post-office box, a private mailbox at a mail-receiving agency and a front door are three different things that all look like addresses. The words the postal operator uses itself settle which — and a recognised box line replaces the street rather than sitting beside it, because that is what a box does.
Does the place exist?
The postcode is checked against the national directory, and the building is looked for in the country's own address register. Both answers carry their own limits: a postcode can be live, retired or absent, and a register only settles existence when its publisher says it lists every address.
The nine kinds of delivery point
Detection is deliberately conservative. Some spellings only count at the start of a line and with a number after them, because a Swedish "Box", a Finnish "PL" and a Spanish "Apartado" are ordinary words elsewhere; words that look like a box but name a flat — the Belgian "bus" — classify nothing at all.
| address_type | what it means |
|---|---|
| street | An ordinary street delivery point: a place, where somebody can be visited or served. |
| po_box | A post-office box, in the operator’s own words — PO Box, Postfach, Boîte Postale, Casella Postale, Skr. poczt., 私書箱. |
| private_mailbox | A box rented at a mail-receiving agency, written the way the postal service requires: a PMB or # number after a real street address. |
| general_delivery | Held at the counter for collection: General Delivery, Poste Restante, Postlagernd. |
| rural_route | A rural route or highway contract route rather than a numbered street address: RR, HC, RFD. |
| military | Military and diplomatic mail: APO, FPO, DPO, PSC, CMR. The address is a routing instruction, not a place. |
| parcel_locker | An automated parcel machine such as a Packstation or a Paczkomat. |
| bulk_mail | A business-volume arrangement that replaces the street address: the French CEDEX, TSA and CS, the Dutch Antwoordnummer. |
| unknown | No box naming is carried for that country, so nothing was classified. Not the same answer as street. |
A private mailbox is the one box that keeps its street line: it stands at a real address, so the street stays and the box number moves into the unit field. What a private mailbox is, and why a box cannot prove where you live explains the addressing rule it is read from.
What a postcode settles, and what it does not
A postcode is a routing unit, not an address. The check tells you whether the code matches its country's pattern, and — where a national directory is installed — whether it exists at all and whether it is live or has been retired. A retired postcode is usually a real address with an out-of-date code rather than a typo, which is why it is scored rather than refused.
Coordinates come with the same care: they are the centroid the directory publishes for the postcode, never a rooftop, and the answer says so in location_source rather than leaving you to assume precision that is not there. What open data cannot give you is the other direction — the list of addresses inside a postcode. Why a UK postcode is not an address sets out what the open releases carry and what a licence buys.
How many companies are registered at an address
An open company register names a registered office for each company on it, so an address can be counted. Past a published threshold of 25 companies at one address, the answer marks it as a mail drop and says which source decided — the operator's own published branch list, or the company count. These are real counts from the installed register, measured through this lookup on 5 September 2026; the last row is the control.
| address | companies_registered |
|---|---|
| 71-75 Shelton Street, London WC2H 9JQ | 86,788 |
| 128 City Road, London EC1V 2NX | 42,851 |
| 20-22 Wenlock Road, London N1 7GU | 15,649 |
| 27 Old Gloucester Street, London WC1N 3AX | 15,259 |
| 10 Downing Street, London SW1A 2AA | 0 |
A count is a fact about a public register and about a place. Formation agents, accountants and mailbox operators all serve honest businesses, and a high count on its own accuses nobody: it tells you the address is a service address rather than an office, which is a useful thing to know when an address is being used as evidence of where somebody is.
Why the kind of delivery point matters
Plenty of rules turn on it. A United States bank opening an account must obtain a residential or business street address for an individual, so a post-office box on its own does not satisfy the customer identification requirement. A company registered in the United Kingdom must keep its registered office at an "appropriate address" — one where a document delivered by hand or post would be expected to reach somebody acting for the company, and where delivery can be acknowledged — a test a box number alone does not meet.
None of that makes a box address wrong. It makes it a different kind of address, which is why the answer names the kind instead of collapsing everything into valid and invalid. How to read an address-existence answer covers the other half: what premise, street and postcode matches each prove, and what absence proves.
What this server holds today
Read live from the sync bookkeeping, so it is what the checks above actually ran against, not a marketing claim. Every answer also names the datasets it used and the version installed at the time, so it can be checked against the file that produced it.
| postcode directory | version | postcodes | live | terminated |
|---|---|---|---|---|
| United Kingdom ons-postcode-directory | 2026-08 | 2,665,797 | 1,760,216 | 905,581 |
BT postcodes are excluded from the United Kingdom directory: reusing them needs a separate Land & Property Services licence, so an address with one is answered as though no directory were installed rather than as though the postcode did not exist.
| address register | countries | coverage | version | addresses |
|---|---|---|---|---|
| ch-gebaeudeadressverzeichnis | Switzerland | complete | 2026-09-06 | 3,188,792 |
| at-adressregister | Austria | complete | 2026-04-01 | 2,514,543 |
| cz-ruian-adresni-mista | Czechia | complete | 2026-07-31 | 2,621,836 |
Company counts come from 3,510,720 addresses compiled from 4 open company registers (United Kingdom, United States). 5,947 branch addresses published by 2 mailbox operators (United States) back the mail-drop flag; the answer names the operator that matched.
What this checker will not tell you
- Whether post actually arrives.That answer, with the postal service's own agency, vacant and residential flags, is licensed. The fields exist and answer "not checked" rather than a guess.
- The addresses at a postcode.Every full UK list derives from a licensed file. The endpoint for it answers 501 rather than approximating one.
- That an address does not exist, from a partial register.Where a register covers only part of a country, absence is answered as null — not evaluated — and adds nothing to the score.
- Who is there.Nothing in the response is about a person: no resident, no occupancy, no name at an address. The product is about places, and no field will ever say otherwise.
Frequently asked questions
Does this tell me whether post is actually delivered there?
No, and nothing on this page pretends otherwise. Whether an address receives post — with the postal service’s own agency, vacant and residential flags — is licensed data in every country that sells it. Those fields answer deliverability_checked: false rather than a guess. What the checker does answer is whether the address stands as written for its own country, what kind of delivery point it names, whether its postcode exists, and what the public registers say about the building.
Can I get the list of addresses at a UK postcode?
Not from open data. Every full UK address list derives from Royal Mail’s Postcode Address File, which is licensed; the open releases go as far as postcodes and their centroids, not the addresses inside them. The API endpoint for it exists and answers 501 ADDRESS_LIST_UNAVAILABLE while no licensed partner is configured, so nothing changes for your client if one is ever signed.
How do you know an address is a private mailbox?
From the way the postal service requires it to be written. Mail to a customer of a commercial mail receiving agency in the United States must carry a PMB or # followed by the box number, and that spelling is exactly what the checker reads. It is a reading of the address, not a licensed flag: an agency address written without the box number reads as an ordinary street address, and saying so is better than inventing a match.
What does exists: null mean?
That no register answered about the building. Either no national address register covers that country, or the register that does covers only part of it. Null means not evaluated, never no. exists is true only on a building match, and false only when the register that answered claims to list every address in its country — so absence from a partial register is never treated as evidence that an address does not exist.
Does a high count of companies mean the address is fake?
No. It means a lot of companies give that address as their registered office, which is what a formation agent, an accountant or a mailbox operator is for. The count is a fact about a public register and about a place; it is never a judgement about a person, and the response carries no field saying who lives or works anywhere.
Is there a limit on this free check?
Ten checks a minute per visitor, and repeats of the same address are answered from a short shared cache. For volume there is an API with batches of 100 addresses per call, a browser endpoint for publishable keys, and 10 free lookups a month with no card required.
Every field, every reason and every weight is written out in the address verification guide, and the product page lists the datasets and their licences.
Need this at scale?
The Spaw API runs the same checks plus mailbox-level SMTP verification, batch and bulk endpoints, and list monitoring — 10 free lookups a month, no card required.