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Where the postcode data comes from

Updated

The plugin looks postcodes up in data that ships inside it. This article explains where that data comes from, what it covers and how it stays current.

Japan Post’s postcode files

Japan Post publishes two files of postcodes for anyone to use:

  • the postcodes of addresses, about 120,700 of them;
  • the postcodes Japan Post assigns to a single large business, such as a company’s head office or a government office, about 22,200 of them.

Version 1.0.0 carries Japan Post’s release of 30 September 2026, about 142,900 postcodes in all. Japan Post states that it does not claim copyright on this data and that anyone may redistribute it: Japan Post’s notes on the postcode data, in Japanese.

How the data is stored

The data sits in the plugin’s assets/data folder, in 1,000 small files, one for each set of first three digits. When a customer types a postcode, the browser loads only the one file it needs, from your own site. No database table is created and nothing has to be imported.

Keeping the data current

Japan Post adds, changes and retires postcodes every month. New versions of the plugin bring newer data, and the changelog says which Japan Post release each version carries, so keep the plugin up to date to get the latest postcodes.

A postcode the data does not list is not an error. The customer types the address as they would without the plugin.

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