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Introspection

GraphQL allows clients to ask a server for information about its schema. GraphQL calls this introspection.

We can ask GraphQL for this information by querying the __schema meta-field, which is always available on the root type of a Query per the spec.

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query {
  __schema {
    types {
      name
    }
  }
}

Example:

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type Query {
  author(id: ID!): Author
}

type Author {
  posts: [Post!]!
}

type Post {
  title: String!
}

If we were to send the introspection query mentioned above, we would get the following result:

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{
  "data": {
    "__schema": {
      "types": [
        {
          "name": "Query"
        },
        {
          "name": "Author"
        },
        {
          "name": "Post"
        },
        {
          "name": "ID"
        },
        {
          "name": "String"
        },
        {
          "name": "__Schema"
        },
        {
          "name": "__Type"
        },
        {
          "name": "__TypeKind"
        },
        {
          "name": "__Field"
        },
        {
          "name": "__InputValue"
        },
        {
          "name": "__EnumValue"
        },
        {
          "name": "__Directive"
        },
        {
          "name": "__DirectiveLocation"
        }
      ]
    }
  }
}

If we query a single type with __type:

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{
  __type(name: "Author") {
    name
    description
  }
}

We’ll get:

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{
  "data": {
    "__type": {
      "name": "Author",
      "description": "The author of a post.",
    }
  }
}

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