JSON Schema Validator

Overview

JSON Schema Validator is a powerful tool for validating JSON data against predefined schemas. It ensures that your JSON data conforms to expected structures, data types, and constraints.

Features

Supported JSON Schema Keywords

• type: Validate data type (string, number, integer, boolean, array, object, null)
• properties: Define object property schemas
• required: Specify required object properties
• additionalProperties: Control whether extra properties are allowed
• items: Define array item schemas (single schema or tuple validation)
• minItems / maxItems: Set array length constraints
• uniqueItems: Require all array items to be unique
• enum: Restrict values to a specific set
• const: Require an exact constant value
• minimum / maximum: Set numeric range constraints
• exclusiveMinimum / exclusiveMaximum: Exclusive numeric bounds
• multipleOf: Require values to be multiples of a number
• minLength / maxLength: Set string length constraints
• pattern: Validate strings against regex patterns
• format: Validate built-in formats (email, uri, etc.)
• allOf: Data must match all sub-schemas
• anyOf: Data must match at least one sub-schema
• oneOf: Data must match exactly one sub-schema
• $ref: Reference another schema (basic support)

Example Usage

Basic Object Validation

JSON Data:

{
  "name": "John Doe",
  "age": 30,
  "email": "[email protected]"
}

JSON Schema:

{
  "type": "object",
  "properties": {
    "name": { "type": "string", "minLength": 1 },
    "age": { "type": "integer", "minimum": 0, "maximum": 150 },
    "email": { "type": "string", "format": "email" }
  },
  "required": ["name", "age"]
}

Array Validation

JSON Data:

{
  "tags": ["javascript", "typescript", "vue"]
}

JSON Schema:

{
  "type": "object",
  "properties": {
    "tags": {
      "type": "array",
      "items": { "type": "string" },
      "minItems": 1,
      "uniqueItems": true
    }
  }
}

Nested Object Validation

JSON Data:

{
  "user": {
    "id": 123,
    "profile": {
      "firstName": "Jane",
      "lastName": "Smith"
    }
  }
}

JSON Schema:

{
  "type": "object",
  "properties": {
    "user": {
      "type": "object",
      "properties": {
        "id": { "type": "integer" },
        "profile": {
          "type": "object",
          "properties": {
            "firstName": { "type": "string" },
            "lastName": { "type": "string" }
          },
          "required": ["firstName", "lastName"]
        }
      },
      "required": ["id", "profile"]
    }
  }
}

Common Validation Errors

Error	Cause	Solution
Missing required field	Required property not found	Add the missing property
Expected type X, got Y	Data type mismatch	Correct the data type
Additional property not allowed	Extra property when additionalProperties: false	Remove extra property or allow it
String does not match pattern	Regex pattern validation failed	Update string to match pattern
Array must have at least X items	Array too short	Add more items or adjust minItems
Value must be one of	enum constraint failed	Use one of the allowed values

Supported JSON Schema Versions

• draft-04
• draft-06
• draft-07
• 2019-09
• 2020-12

Tips for Writing Effective Schemas

1. Use descriptive property names - Makes validation errors clearer
2. Set appropriate constraints - Balance flexibility with strictness
3. Document your schemas - Use description and title fields
4. Test edge cases - Validate with boundary values
5. Use additionalProperties: false - Catch typos in property names
6. Leverage required sparingly - Only enforce truly mandatory fields