PostalCode is an iPhone app with Japan's complete postal code database built in. Type a 7-digit postal code and tap Search to get the address instantly. Or use the three-level address picker — prefecture, city, street — to reverse-look up the postal code for any location. Tap a result to see it on a geocoded map with a red marker. Everything works without an internet connection after the first launch.
Type the 7-digit postal code into the search field and tap Search. The matching address — prefecture, city, and street — appears in the results immediately. The Search button stays disabled until exactly 7 digits are entered, preventing accidental searches with incomplete input.
Use the Address Search section to pick a prefecture, then a city, then a street from cascading pickers. As soon as you select a street, the matching postal code appears automatically. Perfect for when you know the address but need the code.
Japan's entire postal code dataset is bundled inside the app. On first launch, the data is loaded into an on-device database. Every search after that runs locally with no internet required — useful in basements, tunnels, rural areas, or airplane mode.
Tap any search result to open the detail screen. The app geocodes the address and shows it on a map with a red marker at street-level zoom. Postal code, full address, and map — all on one screen.
The Postal Code Search section accepts 7-digit numeric input. The Search button activates only when exactly 7 digits have been entered. After tapping Search, the result appears in the results section formatted as 〒XXX-XXXX with the full address below it. If no address matches, the app tells you clearly so you can check for a typo. Previous results are cleared before each new search so the display is never confusing.
The Address Search section uses three cascading pickers. Selecting a prefecture loads the list of cities in that prefecture. Selecting a city loads the street list. Selecting a street triggers an automatic search and displays the corresponding postal code in the results section — no button tap needed. The pickers update asynchronously in the background so the interface stays responsive throughout.
Every search result is a tappable navigation link. Tap it to open the detail screen, which shows the formatted postal code and full address at the top, and a geocoded map below. A red marker pinpoints the location. If geocoding takes a moment, a loading indicator appears while the coordinates are resolved. The map uses street-level zoom so you can recognize the surrounding area.
The postal code data is shipped as a TSV file bundled inside the app. On first launch, it's imported into a SwiftData database stored on the device. All subsequent searches query that local database directly — no API calls, no rate limits, no latency from network conditions. You don't need to create an account or sign in to use any feature.
Tap the postal code input field and type the 7-digit number using the numeric keyboard. The Search button becomes active when 7 digits are entered. Tap it and the matching address appears in the results section. Tap the result to see it on a map.
In the Address Search section, select a prefecture from the first picker. The city picker updates automatically. Select a city and the street picker updates. Select a street and the matching postal code appears in the results section without any additional button tap.
Tap any result in the search results section to open the detail screen. The app geocodes the address and displays a map with a red marker at the correct location. The formatted postal code and full address are shown above the map for easy reference.
"I fill out shipping forms every day and I'm always looking up postal codes from addresses I already know. The reverse lookup — pick prefecture, city, street, get the code — is exactly what I needed. No more typing addresses into a browser just to find a seven-digit number."
"I work at sites that often have no signal. The fact that everything is stored on the device means it works the same underground as it does in the office. The map view is a bonus I didn't expect to find this useful."
"Used this constantly during a move. Went back and forth between looking up postal codes from addresses and addresses from postal codes. Having both directions in one app, offline, with no account required — it just worked."
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