JSON to GraphQL Type Definitions Generator

JSON to GraphQL Type Definitions Generator

Paste any JSON object or array and instantly receive a GraphQL Schema Definition Language (SDL) document that describes its shape. The generator walks the JSON tree, infers scalar types, names nested objects, merges array-of-object variants, and emits an optional root Query type so the output is ready to drop into a server like Apollo, Yoga, Mercurius, or graphql-go.

Why a Deterministic JSON to GraphQL SDL Converter Matters

Hand-writing GraphQL types from a sample payload is mechanical but error-prone. A single missed nullable, an inconsistent Int vs Float, or a forgotten non-null marker on a list element can break code generation for every downstream client. A rules-driven generator treats the same JSON sample identically every time, which makes it safe to regenerate on every API change.

How to Use

1. Paste a JSON object or array into the input box, or click Try an example to load a representative payload.
2. Set the Root Type Name if you want something other than Root.
3. Choose a Field Nullability strategy – strict (!) for required fields or all nullable for prototyping.
4. Toggle ID Detection to auto-promote id and *Id keys to the GraphQL ID scalar.
5. Optionally include a root Query type with single-entity and list-entity fields.
6. Copy the SDL or download it as schema.graphql.

Features

• Scalar Inference – distinguishes String, Int, Float, Boolean, and ID deterministically.
• Nested Object Types – generates a separate named type for every nested object using PascalCase from the field key.
• Array of Object Merging – unions every field across array items so optional fields are correctly marked.
• Nullable vs Non-Null Toggle – emit strict ! markers or relax everything to nullable for early prototypes.
• Auto ID Detection – upgrades id, userId, orderId style keys to the ID scalar.
• Root Query Scaffold – optional type Query { ... } with single and list resolver signatures.
• Client-Side Only – your JSON never leaves the browser, so the tool is safe for sensitive payloads.

Type Inference Rules

• Integer numbers map to Int; numbers with a fractional part map to Float. A field seen as both promotes to Float.
• Strings map to String. With ID detection on, keys named id or ending in Id become ID.
• Booleans map to Boolean.
• null values mark the field as nullable so the generated SDL skips the trailing !.
• Empty arrays default to [String] because no element type can be inferred safely.
• Arrays of objects merge into one named type; fields missing from any element become nullable automatically.

Who Uses It

• Backend engineers wrapping a REST endpoint or a JSON file in a GraphQL gateway.
• Frontend developers prototyping a schema against a fixture payload before the API is ready.
• API designers documenting third-party response shapes as a typed contract.
• Code-generation pipelines that need a reproducible SDL artefact from a stable JSON sample.