GraphQL Schema Generator

GraphQL schema generator for a structured SDL starting point

The GraphQL schema generator turns a compact type description into a Schema Definition Language document. Enter one type per line, choose Query, Mutation, Input, and simple pagination, and the tool builds a consistent API starting point. Names and type references are checked in the component, preventing empty argument lists, missing Input definitions, and extra SDL fragments hidden in invalid input.

GraphQL and the role of Schema Definition Language

A schema is the central GraphQL contract. It defines available types, fields, arguments, and return values, while client tools use it for completion and query validation. SDL is the textual representation of that contract. A type User definition describes an output object, input UserInput describes values accepted by operations, type Query defines reads, and type Mutation defines changes. The generator creates structure, but resolvers and access rules remain application responsibilities.

Input format

User: id: ID!, name: String!, email: String!, age: Int
Post: id: ID!, title: String!, author: User

Every non-empty line starts with a type name, a colon, and comma-separated fields. Each field uses the name: Type format. Supported references include built-in scalars, declared object types, DateTime, lists, and non-null markers such as [String!]!. A name must begin with a letter or underscore. The __ prefix belongs to introspection and is rejected.

What each option generates

Required values, lists, and references

An exclamation mark after a type means non-null. String! cannot be null, [String!] is an optional list of non-null elements, and [String!]! also requires the list itself. The generator preserves list semantics in output types. In the automatically built Input it removes only the outer non-null requirement, producing a flexible starting point. Required input fields should then be selected according to domain rules.

Queries without invalid empty arguments

For a first type named User, the tool emits user(id: ID!): User and users: [User!]!. Enabling pagination adds limit and offset arguments to the list. With pagination disabled it does not write an empty users() pair, because SDL permits parentheses only when a field actually declares arguments. That small detail determines whether a parser accepts the schema.

Input, Mutation, and the boundary of automation

GraphQL input and output types belong to different categories. An output object called User cannot directly become the type of a field inside UserInput; a separate nested input definition would be necessary. The generator therefore stops with a clear message when the first definition contains an object relationship and Input is requested. Mutation also requires both Query and Input. These checks prevent a document that looks complete but references a definition that does not exist.

Name validation and generated document safety

The form is a convenient interface, not a trust boundary. The component rechecks total length, type and field counts, duplicates, reserved names, and the type-reference grammar. Braces, directives, and additional definitions cannot be smuggled into a field name or type. The output is displayed as text and is never executed by the server. You should still run a GraphQL parser and application integration tests before deployment.

How to prepare a schema step by step

1. Start with the main resource and list its stable fields with scalar types.
2. Add more types on separate lines when output fields reference objects.
3. Enable Query for record and list reads; add pagination for a potentially large collection.
4. Enable Input and Mutation only when the first type has fields suitable for input values.
5. Copy the SDL and add descriptions, enums, directives, interfaces, and domain-specific input types.
6. Run a schema parser, implement resolvers and authorization, add complexity limits, and test operations.

Working with JSON, client types, and configuration

A GraphQL response is JSON, so a sample payload can first be checked with the JSON validator. Once the contract is stable, code generation tools can derive client types; configure a TypeScript project with the tsconfig generator. For a formal description of standalone JSON documents rather than a graph API, use the JSON Schema generator. The formats solve different problems: SDL defines an API graph and its operations, while JSON Schema defines the shape of a document.

Frequently asked questions