# Reference

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This page was generated from content adapted from the [AWS Developer Guide](https://github.com/awsdocs/iam-user-guide.git)
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## IAM identifiers

* **Note**\
  When you use ARNs to identify resources in an IAM policy, you can include *policy variables*. Policy variables can include placeholders for runtime information (such as the user's name) as part of the ARN. For more information, see [IAM policy elements: Variables and tags](https://github.com/kevinslin/aws-reference-notes/blob/main/services/aws_identity_and_access_management_iam/reference_policies_variables.md)

## Quotas, name requirements, and character limits

* **Note**\
  To get account-level information about IAM usage and quotas, use the [GetAccountSummary](https://docs.aws.amazon.com/IAM/latest/APIReference/API_GetAccountSummary.html) API operation or the [get-account-summary](https://docs.aws.amazon.com/cli/latest/reference/iam/get-account-summary.html) AWS CLI command.

## Signing AWS API requests

* **Important**\
  If you use an AWS SDK or AWS command line tool to send API requests to AWS, these tools sign the API requests for you. You must only sign AWS API requests as described in this documentation if you do not use an AWS SDK or AWS command line tool to send AWS API requests.