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A service to retrieve UK addresses by postcode.

The service consumes the OS Apis (https://apidocs.os.uk/), specifically the DPA dataset (https://apidocs.os.uk/docs/os-places-dpa-output).


npm i @planning-inspectorate/address-lookup

And add the API key in .env of your project:

OS_PLACES_API_KEY = {insert key}

You can then use the service importing

import {findAddressListByPostcode} from "@planning-inspectorate/address-lookup";
const {errors, addressList} = await findAddressListByPostcode('EC2M7PD', {maxResults: 10});


The function needs a postcode parameter with the postcode and an optional options parameter to refine the query.

This is the structure:

 postcode: string, 
 options: {
    maxResults: integer, 


postcode should be a string.

It does not get validated inside the function: in case it's not valid the API will just return an empty list of addresses.

A previous validation of it could be useful to prevent useless requests.

  • ⚠️ The OS Api does not require specifically postcodes. The string could be a street or a geographical indication as well. However that's not the purpose of this function


options is optional and contains two parameters.


Should be an integer.

Set the maximum number of results (could possibly be less if the API can't find enough) returned by the function.

Default is 100.

Return value:


If the API key is defined and the postcode is valid, the function will return an object containing a property named addressList

const {addressList} = await findAddressListByPostcode('EC2M7PD');

addressList is an array of objects with this structure:

    apiReference: string, //unique reference
    addressLine1: string, // street number and street name
    addressLine2: string, //extra info like flat number or organisation name, most likely empty
    displayAddress: string, // string to be displayed in the dropdown: extra info, number and street, town, postcode
    postcode: string,
    town: string
  • ⚠️ findAddressListByPostcode is an async function. Will return a Promise if used without the await
  • ⚠️ addressList can be empty if the API can't find any match with the given postcode. Always check for errors


If the function does not return an addressList then an error has occurred. In that case it will return:

const {errors} = await findAddressListByPostcode('EC2M7PD');

errors is an object and it's meant to be integrated with the GOVUK design system mechanism to show error messages (hence its structure with the msg property).
This is its structure:

    apiKey?: {msg: string}
    postcode?: {msg: string}


The apiKey property will be defined when the function cannot find an API key.

The content of the message will be:

An error occurred, please try again later

Cannot be more specific because this is meant to be shown to users. However an error log will explaing what's happening.

When the api key error message is returned, addressList is also returned as an empty array


The postcode property will be defined when the API cannot find any address or for any not-200 response of the OS API.

The content of the message will be:

Enter a valid postcode

When the postcode error message is returned, addressList is also returned as an empty array


To execute Jest tests for the function and its utilities, run

npm run test

To verify the actual response of the function run


It will return some address for a specific postcode hardcoded in src/dev.js. It can be changed without affecting anything else.


npm i @planning-inspectorate/address-lookup

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