Japan Postal Validator

Japanese postal code (郵便番号, yūbin bangō): seven digits behind the 〒 mark

The Japanese postal code is a 7-digit number written as NNN-NNNN and preceded by the 〒 symbol (the postal mark, derived from the katakana テ of teishin, the old Ministry of Communications). The current 7-digit format was introduced by Japan Post on 2 February 1998, extending the original 3-digit/5-digit system in place since 1 July 1968. The validator on this page checks the structural format — three digits, an optional hyphen, then four digits — accepting both 〒100-0001 and the bare 1000001.

The first three digits identify the delivery area (prefecture down to a city or ward), and the last four narrow it to a town, district or large building. There is no check digit: validity is defined by membership in Japan Post's master file, the KEN_ALL.CSV dataset, published monthly, which maps every code to its prefecture (todōfuken), municipality (shikuchōson) and town (chōiki) in both kanji and katakana.

How the seven digits are structured

• Digit 1: broad region (e.g. 0 Hokkaidō, 1 Tokyo, 5 Osaka/Kinki, 9 Tōhoku/Hokuriku).
• Digits 1–3: the old pre-1998 code — still the area sorting key.
• Digits 4–7: town / block, or a dedicated code for a high-volume recipient (a skyscraper, a large company, a PO box bank).
• 〒 prefix: optional in data, customary on printed mail and forms.

Where it shows up

• Address auto-fill: nearly every Japanese checkout form looks up the 7-digit code and fills prefecture + city + town automatically (the famous yūbin bangō kara jūsho lookup).
• E-commerce & logistics: Yamato (Kuroneko), Sagawa and Japan Post all route on the code; an invalid one stalls the shipment.
• Forms & tax: tax returns, residence registration (jūminhyō) and bank KYC all require it.
• Mock data / testing: generating valid-format codes for fixtures and address-form QA.

Gotchas

• Format-valid ≠ real: 999-9999 passes the regex but may not exist in KEN_ALL.CSV. Use the official dataset for true existence checks.
• Full-width digits: Japanese input often produces full-width characters (１００); normalise to half-width before validating.
• Big-building codes: some codes map to a single tower, so the last four digits are not a geographic block — don't infer coordinates from them.
• Monthly churn: codes are added and retired every month; cache the dataset, don't hard-code.

FAQ

Is the hyphen required? No. 100-0001 and 1000001 are equivalent; the hyphen is purely a readability convention after the third digit.

Does Japan have a check digit? No. The code is validated by lookup against Japan Post's master table, not by an arithmetic checksum.

What is the 〒 symbol? It is Japan's postal mark, registered in 1887. On envelopes and forms the boxes for the code are usually printed right after it.