Understanding JSON Schema

JSON Schema is a powerful tool for validating the structure of JSON data. However, learning to use it by reading its specification is like learning to drive a car by looking at its blueprints. You don’t need to know how an electric motor fits together if all you want to do is pick up the groceries. This book, therefore, aims to be the friendly driving instructor for JSON Schema. It’s for those that want to write it and understand it, but maybe aren’t interested in building their own car—er, writing their own JSON Schema validator—just yet.



This book describes JSON Schema draft 2020-12. Earlier versions of JSON Schema are not completely compatible with the format described here, but for the most part, those differences are noted in the text.

Where to begin?

  • This book uses some novel conventions for showing schema examples and relating JSON Schema to your programming language of choice.
  • If you’re not sure what a schema is, check out What is a schema?.
  • The basics chapter should be enough to get you started with understanding the core JSON Schema Reference.
  • When you start developing large schemas with many nested and repeated sections, check out Structuring a complex schema.
  • json-schema.org has a number of resources, including the official specification and tools for working with JSON Schema from various programming languages.
  • There are a number of online JSON Schema tools that allow you to run your own JSON schemas against example documents. These can be very handy if you want to try things out without installing any software.


There is also a print version of this document.