The graphql-ruby is a gem. Also the community is super helpful.
We're transitioning our jbuilder powered JSON apis to a GraphQL endpoint. In production some of our JSON endpoints are delegating requests our GraphQL endpoint, this makes our transition easier since we can rely on existing tests and do benchmarking. The most time so far we've spent on security. Because a client can request everything we've to ensure we're not exposing private data and have some default safety mechanisms so other team members feel safe to work on GraphQL.