How to Validate JSON Payloads Against JSON Schema Specifications

Knowing that a string is syntactically valid JSON only tells you that its brackets and quotes match—it does not guarantee that userId is an integer rather than null, or that email is actually present before your backend writes to a database.

JSON Schema solves this by letting you define a declarative contract—written in JSON itself—that specifies the exact structure, data types, required properties, and value constraints an incoming payload must satisfy.

Anatomy of a Practical JSON Schema

Below is a realistic JSON Schema contract for a product catalog item:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["sku", "name", "price", "inStock"],
  "additionalProperties": false,
  "properties": {
    "sku": {
      "type": "string",
      "pattern": "^[A-Z]{3}-[0-9]{4}$"
    },
    "name": {
      "type": "string",
      "minLength": 2,
      "maxLength": 120
    },
    "price": {
      "type": "number",
      "minimum": 0
    },
    "inStock": {
      "type": "boolean"
    },
    "tags": {
      "type": "array",
      "items": { "type": "string" }
    }
  }
}

Key Validation Keywords Explained

• type: Restricts a value to object, array, string, number, integer, boolean, or null.
• required: An array of property names that must be present on the object. If any key in required is missing, validation fails immediately.
• additionalProperties: false: Rejects unexpected or misspelled fields (for example, if a client accidentally sends priec instead of price).
• minimum / maximum & minLength / maxLength: Enforces numeric bounds and string length limits.
• pattern: Validates strings against a regular expression (which you can test beforehand in the EverySolve Regex Tester).

Step-by-Step: Testing Payloads in EverySolve

1. Open the EverySolve JSON Schema Validator.
2. Paste your JSON Schema definition into the Schema editor and your JSON Instance payload into the Data editor.
3. Click Validate to inspect field-by-field errors—including exact property paths (such as /price or /sku) and which constraint failed.
4. If either document fails to parse as JSON first, format and fix syntax issues with the JSON Formatter.