JSON Schema Validator Online — Validate JSON Against Your Schema

What Is JSON Schema?

JSON Schema is a vocabulary for annotating and validating JSON documents. It describes the structure your JSON data should have: which properties are required, what types they must be, what patterns strings must match, and what numeric ranges are valid. JSON Schema is used to validate API request/response bodies, configuration files, form data, and database documents.

The current specification is JSON Schema 2020-12, used by OpenAPI 3.1 and supported by validators in every major programming language.

How to Use a JSON Schema Validator Online

1. Paste your JSON Schema into the schema panel — the schema defines the expected structure.
2. Paste your JSON data into the data panel — the document you want to validate.
3. Click Validate — the tool runs the JSON data against the schema.
4. Review errors — each error shows the path, expected type/value, and what was received.
5. Fix and re-validate — iterate until all validation errors are resolved.

Key JSON Schema Keywords

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["name", "email"],
  "properties": {
    "name": {
      "type": "string",
      "minLength": 1,
      "maxLength": 100
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "age": {
      "type": "integer",
      "minimum": 0,
      "maximum": 150
    },
    "role": {
      "type": "string",
      "enum": ["admin", "user", "guest"]
    }
  },
  "additionalProperties": false
}

Use Cases

API Request Validation

Validate incoming API request bodies against your schema before processing them. Libraries like ajv (JavaScript), jsonschema (Python), and JSON Schema (Java) make runtime validation straightforward. Catch bad data at the API boundary rather than deep in your business logic.

Configuration File Validation

Many tools (VS Code, Kubernetes) use JSON Schema to validate configuration files and provide IDE autocompletion. Define a schema for your application's config file and validate it at startup to catch misconfiguration errors before they cause subtle runtime failures.

Frequently Asked Questions

What is the difference between JSON validation and JSON Schema validation?

JSON validation checks that a string is syntactically valid JSON (correct brackets, commas, quotes). JSON Schema validation checks that valid JSON data conforms to a specific structure — correct properties, types, and constraints. Both checks are often needed: first validate JSON syntax, then validate against a schema.

Which JSON Schema version should I use?

Use JSON Schema 2020-12 for new projects — it's the latest specification and aligns with OpenAPI 3.1. Draft-07 and Draft 2019-09 are also widely supported. Check which version your validation library supports.

How do I validate nested objects in JSON Schema?

Use $ref to reference reusable schema definitions and nest schema definitions within properties. Arrays of objects use "items": { "$ref": "#/$defs/MyObject" } where $defs contains reusable schemas.

What is the additionalProperties keyword?

Setting "additionalProperties": false means the JSON object must not contain any properties not explicitly defined in the schema. This is useful for strict validation but can cause issues when adding new fields — always consider backward compatibility when tightening schemas.

How do I validate arrays with JSON Schema?

Use "type": "array" with "items" to describe array element schema, "minItems"/"maxItems" for length constraints, and "uniqueItems": true to require distinct elements. For tuples (fixed-length arrays with different types per position), use "prefixItems" in JSON Schema 2020-12.