Tagging Service

A dedicated TaggingService exists in moto.utilities, to help with storing/retrieving tags for resources.

Not all services use it yet, but contributors are encouraged to use the TaggingService for all new features.


When requesting a list of resources, almost all AWS services use pagination to stagger the response. Moto provides a utility class to automatically paginate a response, without having to manually write the logic.

There are three components that make this work:

  1. The Responses-method will call the backend with a max_result/next_token parameter

  2. The backend-method has a plain method that’s decorated with @paginate

  3. A configuration model is supplied to the decorator that contains all the details.

See the below example how it works in practice:

class MyResponse(BaseResponse):

    # The Response-class looks like any other - read the input parameters, and call the backend to retrieve the resources
    def list_resources():
        max_results = 100
        next_token = self._get_param("NextToken")
        # Note that we're getting both the results and the next_token
        # The decorator in the backend returns this tuple
        paged_results, next_token = self.backend.list_resources(
            max_results=max_results, next_token=next_token

from moto.utilities.paginator import paginate
class MyBackend(BaseBackend):

    # The model that contains the configuration required for the paginator
        # key = name of the method in the backend
        "list_resources": {
            # name of the kwarg that contains the next token, which should be passed to the backend
            # backend.list_resources(next_token=..)
            "input_token": "next_token",
            # name of the kwarg that contains the max number of results, which should be passed to the backend
            "limit_key": "max_results",
            # The default limit of the above parameter is not provided
            "limit_default": 100,
            # One or more attributes  that guarantee uniqueness for a given resource.
            # For most resources it will just be an ID, or ARN, which is always unique.
            # An encoded version of these attributes is used as the NextToken.
            "unique_attribute": "arn",
            # Provide a list if only a combination of attributes is guaranteed to be unique
            "unique_attribute": ["start_date", "execution_arn"],
            # By default, an exception will be thrown if the user-provided next_token is invalid
            "fail_on_invalid_token": True  # Default value - no need to specify this
            # This can be customized to:
            #   - silently fail, and just return an empty list
            "fail_on_invalid_token": False,
            #   - throw a custom exception, by providing an exception class
            #     The paginator will `raise CustomException()` or `raise CustomException(invalid_token)`
            "fail_on_invalid_token": CustomException
        # another method that will use different configuration options
        "list_other_things": {

    # The decorator with the pagination logic
    # Note that this method does not have the 'next_token'/'max_results'-arguments
    def list_resources(self):
        # Note that we simply return all resources - the decorator takes care of all pagination magic
        return self.full_list_of_resources

    # If we do need the 'next_token'/'max_results'-arguments, just add them to the function
    # The decorator will only pass them along if required
    def list_other_things(self, max_results=None):
        if max_results == "42":
            # Custom validation magic
        return self.full_list_of_resources