# Welcome
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Welcome to the Amazon Certificate Manager (ACM) API Reference. This guide provides descriptions, syntax, and usage examples for each ACM API operation.

You can use ACM to manage SSL/TLS certificates for your Amazon-based websites and applications. For general information about using ACM, see the [Amazon Certificate Manager User Guide](https://docs.amazonaws.cn/acm/latest/userguide/).

Instead of using the ACM API directly, you can use one of the Amazon SDKs or command line tools to interact with the ACM API. These tools are available for a variety of programming languages and platforms. For more information, see [Tools for Amazon Web Services](http://www.amazonaws.cn/tools/).

**Signing API Requests**  
You must sign your API requests to ACM using Signature Version 4. When you use the Amazon SDKs and command line tools, they sign API requests for you. If you do not use these tools, you must calculate the signature yourself. For more information, see [Signature Version 4 Signing Process](https://docs.amazonaws.cn/general/latest/gr/signature-version-4.html) in the *Amazon Web Services General Reference*.