These v4 APIs are now frozen. See the API versions available for details of the different API versions available.

This describes the details of the requests and responses you can expect from the addons.mozilla.org API.


All requests should be made with the header:

Content-type: application/json


Status Codes

There are some common API responses that you can expect to receive at times.

GET /api/v4/...
Status Codes:

Bad Requests

When returning a HTTP 400 Bad Request response, the API will try to return some information about the error(s) in the body of the response, as a JSON object. The keys of that object indicate the field(s) that caused an error, and for each, a list of messages will be provided (often only one message will be present, but sometimes more). If the error is not attached to a specific field the key non_field_errors will be used instead.


    "username": ["This field is required."],
    "non_field_errors": ["Error not linked to a specific field."]

Unauthorized and Permission Denied

When returning HTTP 401 Unauthorized and HTTP 403 Permission Denied responses, the API will try to return some information about the error in the body of the response, as a JSON object. A detail property will contain a message explaining the error. In addition, in some cases, an optional code property will be present and will contain a constant corresponding to specific problems to help clients address the situation programmatically. The constants are as follows:




The Authorization header is invalid.


The signature of the token indicates it has expired.


The token was impossible to decode and probably invalid.

Maintenance Mode

When returning HTTP 503 Service Unavailable responses the API may be in read-only mode. This means that for a short period of time we do not allow any write requests, this includes POST, PATCH, PUT and DELETE requests.

In case we are in read-only mode, the following behavior can be observed:

  • GET requests behave normally

  • POST, PUT, PATCH, and DELETE requests return 503 with a json response that contains a localized error message

The response when returning HTTP 503 Service Unavailable in case of read-only mode looks like this:

    "error": "Some features are temporarily disabled while we perform websi…"

In case we are not in read-only mode everything should be back working as normal. To check if the site is in read-only mode before submitting a response, the site status api can be called.


By default, all endpoints returning a list of results are paginated. The default number of items per page is 25 and clients can use the page_size query parameter to change it to any value between 1 and 50. Exceptions to those rules are possible but will be noted in the corresponding documentation for affected endpoints.

The following properties will be available in paginated responses:

  • next: the URL for the next page in the pagination.

  • previous: the URL for the previous page in the pagination.

  • page_size: The number of items per page in the pagination.

  • page_count: The number of pages available in the pagination. It may be lower than count / page_size for elasticsearch based paginations that go beyond our max_result_window configuration.

  • count: the total number of records.

  • results: the array containing the results for this page.

Translated Fields

Fields that can be translated by users (typically name, description) have a special behaviour. They are returned as an object, by default, with languages as keys and translations as values, and by default all languages are returned:

    "name": {
        "en-US": "Games",
        "fr": "Jeux",
        "kn": "ಆಟಗಳು"

However, for performance, if you pass the lang parameter to a GET request, then only the most relevant translation (the specified language or the fallback, depending on whether a translation is available in the requested language) will be returned.

Default API behavior

In API version 3 or 4 the response, if the lang parameter is passed, is a single string.

    "name": "Games"

This behaviour also applies to POST, PATCH and PUT requests: you can either submit an object containing several translations, or just a string. If only a string is supplied, it will only be used to translate the field in the current language.

Cross Origin

All APIs are available with Cross-Origin Resource Sharing unless otherwise specified.

Site Status

This special endpoint returns if the site is in read only mode, and if there is a site notice currently in effect. See maintenance mode for more details of when the site is read only and how requests are affected.

GET /api/v4/site/
Response JSON Object:
  • read_only (boolean) – Whether the site in read-only mode.

  • notice (string|null) – A site-wide notice about any current known difficulties or restrictions. If this API is being consumed by a tool/frontend it should be displayed to the user.

v4 API changelog