https://docs.aws.amazon.com/boto3/latest/
I am just linking to the Python version because it’s all on one page. All of the other supported languages are the same - they are all autogenerated from the same definition file by AWS.
Also consider these same APIs are surfaced by the CLI, Terraform, CloudFormation and the AWS CDK.
I’ve been testing writing code and shell scripts against the AWS SDK since 3.5. It helped then, I can mostly one shot it now as long as the APIs were available when it was trained. Now I just have to tell it to “search for the latest documentation” if its a newer API