What draft version does it output?

Draft 2020-12 by default (the current version). Toggle to Draft-07 for compatibility with older validators that haven't upgraded.

Does it detect types correctly?

Usually — primitives, objects, and arrays infer cleanly. Mixed-type arrays (sometimes strings, sometimes numbers) become anyOf. Null values make fields nullable.

Are required fields detected?

Yes — fields present in every sample record are required; fields missing from any record become optional. Small sample sizes can mislead — verify the output.

What about format hints?

Heuristics for common formats: ISO 8601 dates get `format: date-time`, email-shaped strings get `format: email`. Review and refine manually.

JSON Schema Generator | DevTools Surf

DevTools Surf

Example: JSON Schema Generator

A worked example, rendered from real sample data. Sign in to run the tool on your own input.

Input

{"id":1,"name":"John Doe","email":"john@example.com","age":30,"active":true,"tags":["admin","user"],"address":{"city":"NYC","zip":"10001"}}

Output

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "id": {
      "type": "integer"
    },
    "name": {
      "type": "string"
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "age": {
      "type": "integer"
    },
    "active": {
      "type": "boolean"
    },
    "tags": {
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "address": {
      "type": "object",
      "properties": {
        "city": {
          "type": "string"
        },
        "zip": {
          "type": "string"
        }
      },
      "required": [
        "city",
        "zip"
      ]
    }
  },
  "required": [
    "id",
    "name",
    "email",
    "age",
    "active",
    "tags",
    "address"
  ]
}

About JSON Schema Generator

JSON Schema Generator preview - Generators tool

Generate JSON Schema from a sample JSON object. Part of the DevTools Surf developer suite. Browse more tools in the Generators collection.

Use Cases

Generating validation schemas from existing API responses
Creating OpenAPI spec components from sample JSON payloads
Building form validation rules from backend data models
Documenting API contracts by inferring schemas from examples

Tips

Paste a sample API response to auto-generate its schema
Review inferred types and add constraints like min/max manually
Use the generated schema for request validation middleware

Fun Facts

JSON Schema was first proposed by Kris Zyp in 2009 and reached its most recent stable draft (2020-12) after 11 years of evolution.
JSON Schema is used by the OpenAPI Specification (formerly Swagger) to define request and response body structures.
The $ref keyword in JSON Schema enables schema composition, allowing reuse of type definitions across an entire API specification.

FAQ

What draft version does it output?: Draft 2020-12 by default (the current version). Toggle to Draft-07 for compatibility with older validators that haven't upgraded.
Does it detect types correctly?: Usually — primitives, objects, and arrays infer cleanly. Mixed-type arrays (sometimes strings, sometimes numbers) become anyOf. Null values make fields nullable.
Are required fields detected?: Yes — fields present in every sample record are required; fields missing from any record become optional. Small sample sizes can mislead — verify the output.
What about format hints?: Heuristics for common formats: ISO 8601 dates get `format: date-time`, email-shaped strings get `format: email`. Review and refine manually.

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