JSON Schema: A Language for Validating and Annotating JSON
JSON Schema is a domain-specific, declarative language for validating and annotating JSON documents. It provides a standardized way to define the structure, constraints, and metadata associated with JSON-based APIs and data formats, facilitating automated validation, documentation, and related tooling.JSON is excellent for data exchange, but lacks a native mechanism for formally describing its structure and constraints. JSON Schema fills this gap, reducing ambiguity and errors in data interchange.
Why JSON Schema?
JSON Schema draws inspiration from the architecture of the World Wide Web, including concepts such as URIs for identifying and linking schemas. While it can be applied in many domains, these qualities make it especially well-suited for describing and validating data exchanged in web APIs.Validation
Ensure that JSON instances conform to a specific structure and set of constraints. Catch data errors before they cause problems.
Annotation
Attach metadata to values in JSON documents, which can be used by applications for documentation, form generation, and more.
Documentation
Schemas serve as living documentation that describes your data structures in a machine-readable format.
Interoperability
Create a contract for data exchange between systems, ensuring compatibility across different implementations.
Key Features
Self-Describing
A JSON Schema is itself a JSON document, making it easily portable and machine-readable. You can validate schemas, share them across systems, and even generate schemas programmatically.Extensible
JSON Schema includes a flexible extension model that allows third parties to define their own dialects and vocabularies for specific use cases.Standards-Based
JSON Schema is defined through IETF Internet-Drafts and maintained by an active open-source community, ensuring stability and broad industry support.Core Concepts
What is JSON Schema?
Learn about the fundamentals, terminology, and use cases for JSON Schema.
Getting Started
Write your first schema with a practical example that validates JSON data.
A Schema as a Contract
A JSON Schema serves as a contract for data. It is primarily designed for two purposes:- Validation - Ensures that a JSON instance conforms to a specific structure and set of constraints
- Annotation - Attaches metadata to values in a JSON document, which can be used by applications in a variety of ways
Specification Structure
The JSON Schema specification is defined in a series of documents, each addressing a different aspect of the language:- Core Specification - Defines fundamental keywords and concepts (
$schema,$id,$ref,$defs, etc.) - Validation Specification - Defines keywords for structural validation (
type,properties,required,pattern, etc.) - Additional vocabularies - Define specialized keywords for specific use cases
Community and Support
Specification
Read the official IETF specification documents
GitHub
Contribute to the specification and report issues
Website
Explore tools, implementations, and community resources
Next Steps
Understand the Basics
Read What is JSON Schema? to learn about instances, schemas, and validation concepts.
Write Your First Schema
Follow the Getting Started guide to create a working schema example.