Schema Validation

Validate your JSON with JSON Schema. Learn how to define, apply, and test schemas for robust, error-free data.

Why Use JSON Schema?

Data Validation: Ensure your JSON data meets specific requirements
Documentation: Self-documenting data structures
Code Generation: Generate code, forms, and documentation from schemas
API Design: Define clear contracts for API requests and responses

Basic Schema Structure

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "name": {
      "type": "string",
      "minLength": 1
    },
    "age": {
      "type": "integer",
      "minimum": 0
    }
  },
  "required": ["name", "age"]
}

Common Validation Keywords

type: Defines the data type (string, number, object, array, boolean, null)
required: Specifies which properties are mandatory
properties: Defines the properties of an object
items: Defines the schema for array items
minimum/maximum: Sets numeric value limits
minLength/maxLength: Sets string length limits
pattern: Defines a regular expression pattern
enum: Lists allowed values
format: Specifies data format (email, date-time, uri, etc.)

Example: User Profile Schema

Let's look at a more complex example that validates a user profile:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "required": ["id", "username", "email"],
  "properties": {
    "id": {
      "type": "string",
      "pattern": "^usr_[a-zA-Z0-9]{8}$"
    },
    "username": {
      "type": "string",
      "minLength": 3,
      "maxLength": 30
    },
    "email": {
      "type": "string",
      "format": "email"
    }
  }
}

Validation Tools

Several tools can help you validate JSON against schemas:

JSON Schema Validator - Online validator
Ajv - JavaScript validator
JsonSchema Validator - Java validator
jsonschema - Python validator

Best Practices

Always specify the $schema version
Use descriptive property names
Include helpful error messages in descriptions
Validate early in your application pipeline
Keep schemas modular and reusable
Use references to avoid schema duplication

Try It Yourself

Check out our example files: