# Schema ## Overview Hydra input schema is a dialect of the GraphQL schema definition language enriched with the additional directives and built-in primitive types described in what follows. The input schema is consumed by `hydra-cli codegen` to generate the entity classes for the database and the final API GraphQL schema served by the server. The latter is auto-generated and can be previewed by running ``` $ hydra-cli preview && cat apipreview.graphql ``` In windows, you should run: ``` $ hydra-cli preview && type apipreview.graphql ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://dzhelezov.gitbook.io/hydra/docs/schema-spec.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.