Try GET- or POST-requesting this page, with the parameter "zipcode", and a Danish zip code :-)

New: The service now accepts a 

country
parameter, which can be used to switch to Norwegian zipcodes.

Examples

GET http://postnr.io/8000/

GET http://postnr.io/?zipcode=8000

POST http://postnr.io/
Body: zipcode=8000

Result

{"error":false,"message":"","result":"Aarhus C"}

GET http://postnr.io/no/6048/

GET http://postnr.io/?zipcode=6048&country=no

POST http://postnr.io/
Body: zipcode=6048&country=no

Result

{"error":false,"message":"","result":"\u00c5lesund"}