This topic describes how to use the simulation call function of Alibaba Cloud CLI. You can use this function to simulate a call when you need to check if a request to the server is valid but you do not want to perform any action that will affect your resources on the cloud.

You can simulate call by printing and checking a request by using --dryrun.

For example, to check the format of a request generated when the DescribeInstances API of ECS is called, run the following command:

aliyun ecs DescribeInstances --dryrun

The system displays an output similar to the following output:

Skip invoke in dry-run mode, request is:
POST /? AccessKeyId=AccessKeyId&Action=DescribeInstances&Format=JSON&RegionId=cn-hangzhou&Signature=MoLDYgpNzikuFXe%2BY16LXcicPks%3D&SignatureMethod=HMAC-SHA1&SignatureNonce=e473d1c890604d7a917409459fc74ce8&SignatureType=&SignatureVersion=1.0&Timestamp=2019-05-29T09%3A05%3A17Z&Version=2014-05-26 HTTP/1.1
Accept-Encoding: identity
Content-Type: application/x-www-form-urlencoded
x-sdk-client: golang/1.0.0
x-sdk-core-version: 0.0.1
x-sdk-invoke-type: common