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JSON Schema Validator / Generator

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Options

Status
Idle
Supported rules
type, required, properties, items
enum, minLength, minimum
additionalProperties: false
type: ["string", "null"]

What is a JSON Schema Validator / Generator?

A JSON Schema Validator / Generator helps you create JSON Schema from sample JSON and validate JSON data against an existing schema.

This is useful for API contracts, backend validation, testing structured responses, and documenting expected payload formats.

How to use the JSON Schema Validator / Generator

  1. Paste JSON into the input field.
  2. Click Generate schema to create a JSON Schema.
  3. Edit or replace the schema if needed.
  4. Click Validate JSON to validate the input against the schema.

Tips

  • Generated schemas are useful as a starting point, but you may want to refine them manually.
  • Validation errors help identify which field or path does not match the schema.
  • Required fields can be toggled when generating object schemas.
  • This tool is useful for APIs, tests, automation, and AI JSON output validation.
  • You can manually add enum, minLength, minimum, nullable types, and additionalProperties false.

Schema design checks

Required versus optional

Mark fields as required only when every valid payload must include them. Optional fields are better for phased API rollouts and partial responses.

Strict additional properties

Use additionalProperties false when unexpected fields should fail validation, but avoid it when clients may send forward-compatible metadata.

Nullable values

Represent nullable fields explicitly with type arrays such as ["string", "null"] so null is not confused with a missing field.

Enums and ranges

Add enum, minimum, minLength, and similar constraints after generation to make the schema closer to the real business contract.

Example JSON Schema

You can also edit the generated schema manually. This version supports common rules such as type, required, enum, minLength, minimum, nullable types, array items, and additionalProperties. 

{
  "type": "object",
  "required": ["name"],
  "properties": {
    "name": {
      "type": "string",
      "minLength": 2
    },
    "age": {
      "type": "integer",
      "minimum": 18
    },
    "status": {
      "type": "string",
      "enum": ["active", "disabled"]
    },
    "nickname": {
      "type": ["string", "null"]
    }
  },
  "additionalProperties": false
}

Related guides

Learn the workflow behind this tool and what to check next.

API contracts

JSON Schema for reliable API contracts

A schema workflow that treats successful and failing payloads as executable documentation rather than relying on one ideal sample.

Read guide
API debugging

How to debug an API JSON response step by step

A repeatable workflow for separating transport errors, JSON syntax problems, and data-contract failures in API responses.

Read guide
APIs and data

How to debug JSON API payloads

A practical workflow for formatting JSON, finding syntax errors, validating payload shape, and checking response status when API data looks wrong.

Read guide

Schema validation checks for real API payloads

Use schema validation to make payload assumptions explicit before they become frontend bugs, backend edge cases, or integration failures.

Required fields

Confirm which fields must exist, which can be omitted, and which can be null without breaking consumers.

Type boundaries

Check arrays, objects, numbers, enums, dates, and string formats against the exact shape your application expects.

Contract drift

Compare sample responses against the schema after API changes, vendor upgrades, or webhook version changes.

Readable errors

Use validation paths to find the exact property that failed instead of scanning a large payload manually.

A practical example, an edge case, and a maintainer note

Practical example

Validate {"age":"18"} against a schema requiring an integer. The JSON is syntactically valid, but the string still violates the API contract.

Edge case

oneOf, anyOf, nullable fields, and additionalProperties can produce surprising results when overlapping schemas accept the same value.

Maintainer note

I keep representative failing payloads beside the schema because error cases expose contract ambiguity faster than a perfect sample.

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JSON Schema Validator / Generator FAQ

Can this tool generate JSON Schema from JSON?
Yes. It can generate a starter schema structure from sample JSON.
Can it validate JSON against a schema?
Yes. It validates JSON using the provided schema and shows validation errors.
Which schema rules are supported?
This version supports common rules such as type, required, properties, items, enum, minLength, minimum, nullable type arrays, and additionalProperties false.
Is my JSON stored?
No. It is processed only in your browser.