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Version: 3.1.0

API Reference - AddressZen

Getting Started



All API methods are either a GET, POST or OPTIONS request.

The API communicates over both HTTPS and plain HTTP using IPv4 and IPv6.

We recommend using HTTPS only although HTTP is available.

We use appropriate HTTP status codes where possible to indicate the request status.

Rate Limiting

Each IP address is rate limited at 30 requests per second. Tripping the rate limit will result in a 503 response.

The autocomplete API also has an additional rate limit.

If you expect to breach the limit please contact us and we can move you to an endpoint with a higher limit.


JSONP requests are supported. Include a callback= in your request as a query parameter. Your results return wrapped in a function designated by your request.


Most requests require an API key for authentication. Authenticate by passing an api_key as part of the query string. For example:

Alternatively, authentication can be transmitted via the Authorization header using the following scheme:

Authorization: api_key="iddqd" [other_key="foo"]


This API is versioned with a simple prefix in the URL. The current version is /v1/. We will maintain backwards-compatibility by releasing breaking changes under a new version.

Please note that the following changes are backwards-compatible:

  • Adding new properties to existing API responses
  • Adding new API endpoints
  • Adding new optional request parameters to existing API endpoints
  • Changing the order of properties in existing API responses
  • Changing the autocomplete address suggestion format

Error Handling

A successful lookup is accompanied with a HTTP status code of 200 and a response code of 2000 (found in the body).

An error has occurred if the HTTP status code is not 200. Errors can range from a benign 404 (resource not found) to more urgent errors (your API Key ran out of credit, failed authentication, etc).


Each new account comes with a free test balance. Contact us if you need more for testing and integration.

Community Key

Our documentation and demos make heavy use of our community key iddqd. This allows for convenient access for trialing the API.

Many restrictions on this key are relaxed to allow developers make test requests. This key has a limit of 15 lookups per IP address per day as well as a daily usage cap. If you hit any limit restrictions, you can continue testing the API by creating a key of your own and using our free test methods.

Please be kind with the community key. We're trusting everyone to use it responsibly so that other developers may trial the API. Thank you!


Requests that affect your balance may be annotated with arbitrary metadata. This data is stored along with your lookup history and can be queried at a later date via the API or the dashboard. We call the ability to label your requests tagging.

Response Codes

The API returns two indicators to help you to determine the status of each HTTP request.

The first is the HTTP Status, which is found in the status-line of all HTTP requests. The API will return status codes that adhere to HTTP /1.1 Specifications wherever possible.

2XX status codes indicates success while 4XX and 5XX indicate client and server errors respectively.

The second is the API response code, which can be found in the code property of the response body. This code will provide a more specific reason if a failure has occurred and can point you in the right direction when debugging.

Please use the glossary of code numbers and HTTP status codes below when debugging your requests.

200 Request Success

HTTP CodeAPI CodeDescription
2002000Success. Request was completed successfully.

400 Bad Request

The request could not be understood due to some input error.

HTTP CodeAPI CodeDescription
4004000Invalid syntax submitted. Some part of your request was malformed or did not match our specifications.
4004001Validation failed on your submitted data. Some of the data you provided did not meet our validation requirements, e.g. string length.
4004005Invalid start date. Please ensure start dates are provided as a UTC Timestamp in milliseconds.
4004006Invalid end date. Please ensure end dates are provided as a UTC Timestamp in milliseconds.
4004007Invalid date range. Check if your start and end dates are in the right order.
4004008Invalid date range. Check that your date range is 90 days or less.
4004009Too many tags. Please specify no more than 3 tags to query.

401 Unauthorised

Authorization credentials are not valid.

HTTP CodeAPI CodeDescription
4014010Invalid Key. The api_key you provided is not valid.
4014011Requesting URL not on whitelist. The cross domain request is not coming from a whitelisted URL. You can update or disable your allowed URLs via your Key settings.
4014012Failed user authentication. Invalid user_token presented.
4014013Licensee Key is required. Sublicensed keys require you need to present licensee credentials via the licensee parameter.

402 Request Failed

Your request is well-formed but are not able to complete your request for another reason.

HTTP CodeAPI CodeDescription
4024020Key balance depleted. You're out of lookups on your API Key.
4024021Limit reached. One of your lookup limits has been breached for today. This could either be your total daily limit on your key or the individual IP limit. You can either wait for for the limit to reset (after a day) or manually disable or increase your limit.

404 Resource Not Found

The resource you requested does not exist.

HTTP CodeAPI CodeDescription
4044040Postcode not found. The postcode you have submitted does not exist.
4044041User not found. Your user could not be identified given the credentials you presented.
4044042Key not found. Your key could not be identified given the credentials you presented.
4044044No UDPRN found. No address is associated with the UDPRN queried
4044045No licensee found. Your licensee could not be identified given the credentials you presented.
4044046No UMPRN found. No Multiple Residence premise is associated with the UMPRN queried.

500 Server Error

A error occurred on our server.

HTTP CodeAPI CodeDescription
5005000An error occurred on our end. These errors are logged and queued so we can understand what went wrong. However, if you need speedy resolution please email support
5005001Akin to 5000.
5005002The server took too long to process on our end, so we aborted the request. You may retry the request.