JSON Schema Generator: Infer Draft-07 Schemas from Sample Data

What is JSON Schema?

JSON Schema is a vocabulary for annotating and validating JSON documents. It defines the expected structure, types, and constraints of your data. Draft-07 is the most widely supported version, compatible with AJV, Joi, Fastify, OpenAPI 3.0, and more.

Why Generate Schemas from Sample JSON?

Writing JSON Schema by hand is tedious and error-prone. Our generator infers the schema directly from your sample payload — perfect for documenting APIs, validating incoming data, or creating OpenAPI spec components.

Schema Inference Rules

• Every key becomes a property with an inferred type
• All keys present in the sample are added to required
• Nested objects generate nested $defs references
• Arrays infer items type from the first element
• Null values generate ["string", "null"] union types

// JSON Input
{ "id": 1, "name": "Alice", "email": "a@example.com", "active": true }

// Generated JSON Schema (Draft-07)
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "required": ["id", "name", "email", "active"],
  "properties": {
    "id":     { "type": "integer" },
    "name":   { "type": "string" },
    "email":  { "type": "string" },
    "active": { "type": "boolean" }
  }
}