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What you want to do can be achieved with both Scalar Types and Enum Types. In your case you probably want to go with an enum because you have a small finite list of allowed values. Using the Enum Type will show the allowed values in the documentation in GraphiQL. In most GraphQL APIs Enum values use all capital values but you could use the value property to transparently map the female value to FEMALE. This would for example allow you to treat the values as lower case on the server side (we do this a lot because the values come in lower case from our postgres). Here some code for inspiration: