What are the three root types in GraphQL?

GraphQL has three root operation types that serve as entry points into the API. Query is the root type for read operations — every field on type Query is a top-level data fetcher. Mutation is the root type for write operations (create, update, delete). Subscription is the root type for real-time event streams. Every GraphQL schema must have at least a Query type. Mutation and Subscription are optional. The schema declaration ties them together: schema { query: Query mutation: Mutation subscription: Subscription }.