Naming types differ from naming fields.

-  type blogPost { # bad
-  type Blog_Post { # also bad
+ type BlogPost { # good
   title: String!
  }

GraphQL comes with built-in scalar types: String, Int, Boolean, Float. All of them are named using UpperCamelCase.

Internal GraphQL Introspection Types such as __Type, __Field, __InputValue also follow this convention with 2 underscores at the beginning.

A lot of projects are using the statically typed nature of GraphQL to generate internal type definitions, many of whom use it for static analysis. Both Flowtype and TypeScript use UpperCamelCase to name complex types.

According to Wikipedia, we should use UpperCamelCase in JavaScript, Java, Swift, and Kotlin for classes and type declarations.

This rule can be validated using graphql-eslint, read more about naming-convention rule.