Skip to content
Spaw
Get your API key

Company number

published · September 10, 2026

A company number is the identifier a national registrar assigns to an incorporated company, unique within that register and never within the world.

A company number is the identifier a national registrar assigns to an incorporated company. It is unique within that register and never within the world, which is why every lookup of one needs to know which country's register to read.

What Spaw answers

One register is installed: the United Kingdom's. A UK number is eight characters, and a shorter one is left-padded with zeros before it is looked up — 445790 and 00445790 are the same company.

The answer carries the legal name, the status in the register's own wording, the jurisdiction, the category, the legal form and the incorporation date, plus register naming the file that answered.

The staleness that has to be stated

The free UK company file is republished monthly and only refreshes within a few working days of month end, so an answer here can be up to five weeks behind the live register. Every response names the date of the copy it read in sources, and the monitor cadences stop at weekly for the same reason: re-checking a monthly file daily would be theatre.

An identifier from a register that is not installed answers unsupported_register, and one no installed register carries answers unknown_identifier. Both mean "not carried here" and neither means the company does not exist.

Related

markdown version: /glossary/company-number.md

Verify addresses the same way

The Spaw API runs every check described here on each lookup, with an SMTP handshake that never sends mail. 10 free lookups a month, no card required.

Get your API key

More glossary

  • ASN

    An Autonomous System Number identifies one network that announces its own routes to the internet under a single routing policy.

  • Address register

    An address register is a country's official file of every address its authorities recognise, usually keyed on buildings rather than letterboxes.

  • CIDR

    CIDR notation writes a range of IP addresses as one address and a prefix length, so 203.0.113.0/24 means the 256 addresses sharing those first 24 bits.

  • Catch-all domain

    A catch-all domain is one whose mail server accepts mail addressed to every recipient, whether or not that mailbox exists.

  • Check digit

    A check digit is a digit computed from the rest of an identifier so that a mistyped one usually fails arithmetic before anybody looks it up.

  • Credit

    A credit is the billing unit of the whole API: one credit buys one fresh lookup that produced a usable answer, on any of the six signals.

  • Datacenter IP

    A datacenter IP is an address inside a range operated by a hosting, cloud or server provider rather than by a consumer access network.

  • Delivery point

    A delivery point is the smallest unit a postal service delivers to: one letterbox, one door, one box at a counter.