CloudFormation templates are written in JSON or YAML. Both support data in key-value pairs, objects, arrays, and so on .YAML also supports additional features such as multi-line strings, comments, and so on. I will also be using YAML for the examples. Since YAML support was introduced later for CloudFormation, you will also see a lot of JSON templates in the web. So, it is also good to have a decent understanding of YAML and JSON. If you are familiar with one, you may also use one of the JSON to YAML or YAML to JSON converters available online.