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JSON Schema

JSON Schema is a vocabulary for describing the structure of JSON documents, defining types, constraints, and validation rules; it is the schema standard for JSON.

Purpose

To give JSON a validation mechanism similar to XSD, ensuring data matches the expected structure.

Mechanism

A schema describes itself in JSON: type declares the type, properties declares object properties, items declares array elements, required declares mandatory fields, and minimum/maximum/pattern declare constraints. Draft 2020-12 is the latest version. Validators (ajv) check documents against it.

Use cases

  • API request/response validation
  • Configuration file checking
  • Form data validation
  • OpenAPI type definitions

Examples

  • Input 
    {"type":"object","properties":{"age":{"type":"integer","minimum":0}}}
    Output 
    Validates that age is a non-negative integer

    Constraint declaration

Common errors

Using an outdated draft version breaks validator compatibility
Pin the draft version and use a matching validator

Related terms

XSD
XSD (XML Schema Definition) is the W3C-standard language for defining XML document structure, describing elements, attributes, and type constraints in XML syntax.
GLOSSARY
DTD
A DTD (Document Type Definition) is the structure-definition mechanism of XML 1.0; it is simpler than XSD but limited, and is written in a special (non-XML) syntax.
GLOSSARY
JSON
JSON (JavaScript Object Notation) is a lightweight data interchange format based on JavaScript object literals, using key-value pairs and arrays.
GLOSSARY

Related tools

JSON Schema Generator
Generate JSON Schema from JSON data. Free, private, 100% client-side.
TOOL
JSON Validator
Validate JSON and pinpoint syntax errors by line and column. Free, private, and 100% client-side.
TOOL

References