"required" property should be a must-have

[manudiv]

[AaronTorgerson]

Agreed. It is rather odd to not be able to specify that "this property must be set from either a file or environment variable - no default is allowable".

[ath88]

I would love this feature.

[arminrosu]

Additionally, the currently suggested way of setting default: null and format: String properties means that typings infer the values as null | undefined. Thus your build will fail if using Typescript, though on runtime only .validate() will throw an error.