Autofill a city and region from a postal code

A faster address form: the moment someone types their postal code, fill the city and region for them. It's one request, no key, and it cuts a few fields off every checkout.

The lookup

curl https://countries.dev/postal/US/10001

[{ "placeName": "New York", "admin1": { "name": "New York" }, "latitude": 40.7484, "longitude": -73.9967 }]

Wire it to the form

When the postal-code field changes, look it up and fill the rest:

zipInput.addEventListener('change', async () => {
  const [place] = await fetch(
    `https://countries.dev/postal/${country}/${encodeURIComponent(zipInput.value)}`,
  ).then((r) => r.json());

  if (place) {
    cityField.value = place.placeName;
    regionField.value = place.admin1?.name ?? '';
  }
});

Because it returns coordinates too, you can also drop a map pin or compute a shipping distance from the same response.

Pair it with a country picker

Let users choose the country first — a country dropdown gives you the ISO code to pass straight into the postal lookup. The full postal code API covers 121 countries, keyless. See the docs for the response shape.