What ZIP code am I in?

How it works

A ZIP code is a set of mail delivery routes, not an area on a map: neighbours can be in different ZIPs, and some ZIPs are a single building or a block of PO boxes. So the answer is not "the ZIP whose shape you are standing in". It is the ZIP on the nearest address point (National Address Database or OpenAddresses), or on the nearest street segment (TIGER) when no address point is close. That is the ZIP to write on an envelope addressed to where you are.

In your code

curl "https://api.geocode.net/v1/reverse?lat=39.1582&lng=-75.5247" -H "X-API-Key: YOUR_KEY"

{ "results": [ { "formatted": "1 W Loockerman ST, Dover, DE 19904",
                 "components": { "city": "Dover", "state": "DE", "zip": "19904" } } ] }

Notes

• Census statistics use ZCTAs (ZIP Code Tabulation Areas), areas drawn from ZIP codes. Add fields=census to get the ZCTA as well; it usually matches the ZIP, but not always.
• ZIP+4 needs USPS data that cannot be redistributed, so it is not offered.
• Nothing is requested until you click, and the position is not stored.