Generate GraphQL Schema
from JSON

GraphQL type definitions in four steps

No account. No upload. No nonsense.

Related JSON tools

Common questions answered

Converting JSON to GraphQL types

GraphQL uses a strongly-typed schema to define queryable data. Each type has field names and types (String, Int, Float, Boolean, ID). This tool generates GraphQL type definitions from JSON, mapping structures to the GraphQL type system — useful when building a GraphQL API from existing JSON data.

The converter maps JSON types to GraphQL: strings → String, numbers → Int or Float, booleans → Boolean, arrays → [Type], nested objects → separate types. Nullable fields use default behavior (nullable unless !). Output is valid SDL for Apollo Server, graphql-yoga, or any framework.

{
  "id": 1,
  "name": "Alice",
  "email": "alice@test.com",
  "posts": [
    {"id": 1, "title": "Hello"}
  ]
}

type User {
  id: Int!
  name: String!
  email: String!
  posts: [Post!]!
}

type Post {
  id: Int!
  title: String!
}

Get the most out of this tool

• GraphQL fields are nullable by default — add ! to required fields manually after generating base types.
• Use separate type definitions for nested objects — it makes the schema reusable across queries.
• Add Query type definitions manually to specify which types are accessible as top-level queries.

GraphQL type definitions from JSON

GraphQL is a query language for APIs that uses a strongly typed schema to define the shape of all data. Unlike REST APIs where the server decides what data to return, GraphQL lets clients specify exactly which fields they need. Every piece of data in a GraphQL API must be described in the schema using type definitions — this is where converting existing JSON data structures to GraphQL types saves significant development time.

The converter maps JSON structures to GraphQL SDL (Schema Definition Language) type definitions. JSON objects become GraphQL types with fields. JSON strings become the String scalar. JSON integers become the Int scalar. JSON floats become the Float scalar. JSON booleans become the Boolean scalar. JSON arrays of primitives become lists: [String], [Int]. JSON arrays of objects become lists of named types: [User]. Nested JSON objects become separate named types.

GraphQL's type system has an important distinction from JSON: non-nullable by default with optional explicit nullability. In GraphQL SDL, a field declared as name: String! is non-null (cannot return null). Without the exclamation mark, name: String is nullable (can return null). This is the opposite of TypeScript's default behavior. The converter marks fields as nullable unless all records in a provided JSON array have that field present and non-null.

The ID scalar is GraphQL's special type for unique identifiers. It accepts both integers and strings but always serializes as a string. JSON fields named "id", "_id", or ending in "Id" or "_id" are typically converted to the ID scalar rather than String or Int. This is a naming convention that this converter follows — fields that appear to be identifiers get the ID type for proper GraphQL semantics.

Custom scalars allow GraphQL to represent types beyond the five built-in scalars (String, Int, Float, Boolean, ID). Date, DateTime, JSON, UUID, URL, and Email are common custom scalars defined in many GraphQL schemas. Fields that look like dates, emails, or URLs in the JSON input are flagged as candidates for custom scalars in the converter output — you replace the generated String type with your preferred custom scalar.

GraphQL type definitions generated from JSON are the starting point for a GraphQL API, not the complete schema. You still need to define Query, Mutation, and Subscription types that reference your data types. You need to define resolvers that fetch and return data. You need to add directives for deprecation, authorization, and caching. But starting with generated types from real JSON data ensures your type definitions match the actual shape of your data from the beginning.

When developers use this tool

Additional frequently asked questions