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The GraphQL schema is at the core of any GraphQL server. It defines the capabilities of the API and specifies how clients can access that data. A schema includes types and fields, queries and mutations, interfaces, and unions. Hoppscotch provides you the functionality to connect to a GraphQL server and explore the GraphQL schema. A GraphQL schema defines types and the fields on those types. This allows clients to ask for exactly what they need and get exactly that - nothing more and nothing less. The schema also defines queries and mutations, which are entry points into the API to read and write data. The schema is written using the Schema Definition Language (SDL). The SDL provides a way to describe types and fields, as well as queries and mutations. Here is a very simple example of a schema in SDL: 
type Query {
  hello: String
}
This schema has one type, Query, and one field on that type, hello. A client could call the hello query to get the String value returned by that field. The schema sits at the core of any GraphQL server and defines the capabilities of the API. Understanding the structure and components of a GraphQL schema is fundamental to building and using GraphQL APIs. Hoppscotch’s GraphQL API platform provides you with the best experience to test and play around with GraphQL. Once connected to a GraphQL server, you can view the schema by clicking the schema icon on the sidebar. For example, try connecting to the following server. 
https://echo.hoppscotch.io/graphql
You’ll see a schema like the one below: 
schema {
  query: Request
}

type Request {
  method: String
  url: String
  headers: [Header]
}

type Header {
  key: String
  value: String
}
The schema has the following types: Request with queries method, URL, and headers, where the header points to another type Header.