# Search by UDPRN

UDPRNs are an eight-digit unique numeric code (e.g. 25962203) for any premise on the Postcode Address File. It's essentially a unique identifier for every address in the UK that Royal Mail has in its database.

To test your implementation of our API we have a range of test [UDPRNs](/docs/api/udprn.md) that yield both successful and unsuccessful responses to your request.

## Example[​](#example "Direct link to Example")

```
/v1/udprn/[UDPRN]?api_key=ak_test
```

```
/v1/udprn/23747771?api_key=ak_test
```