YAML

`.yaml` or `.yml`

According to the Original YAML Website’s FAQ¹, please use .yaml when possible.
According to Official YAML Website’s FAQ², the .yaml extension is preferred but .yml is common and acceptable.

¹

https://github.com/yaml/www.yaml.org/blob/a860a2423cdeb77994034e5a58b2c7ef00153aa7/faq.html#L61

²

https://github.com/yaml/www.yaml.com/blob/ad9b7dee6e2707a9448fbf73de2dda67882d1c16/src/faq.md?plain=1#L12