GraphQL-JS is a reference implementation of the GraphQL spec that also serves as a library for building servers, clients, and tooling for GraphQL. It exports several useful functions such as parse, which can be used to parse queries and schema notation, introspectionQuery, buildClientSchema, printSchema, validate, execute, and buildASTSchema. These functions provide various features for building and working with GraphQL schemas, including parsing and validating queries, printing schemas in a readable format, executing queries on the server, and creating executable schemas. Additionally, it has a little tool kit called graphql-tools that can be used to add resolve functions to a schema created with buildASTSchema.