Conventions used in this book

Language-specific notes

The names of the basic types in JavaScript and JSON can be confusing when coming from another dynamic language. I’m a Python programmer by day, so I’ve notated here when the names for things are different from what they are in Python, and any other Python-specific advice for using JSON and JSON Schema. I’m by no means trying to create a Python bias to this book, but it is what I know, so I’ve started there. In the long run, I hope this book will be useful to programmers of all stripes, so if you’re interested in translating the Python references into Algol-68 or any other language you may know, pull requests are welcome!

The language-specific sections are shown with tabs for each language. Once you choose a language, that choice will be remembered as you read on from page to page.

For example, here’s a language-specific section with advice on using JSON in a few different languages:

Draft-specific notes

The JSON Schema standard has been through a number of revisions or “drafts”. The most important are Draft 7, the most recent at the time of this writing, and Draft 4, on which a lot of production software was built, and the draft for which an earlier version of this book was written.

The text is written to encourage the use of Draft 7 and gives priority to the latest conventions and features, but where it differs from earlier drafts, those differences are highlighted in special call-outs. If you only wish to target Draft 7, you can safely ignore those sections.

New in draft 7

Examples

There are many examples throughout this book, and they all follow the same format. At the beginning of each example is a short JSON schema, illustrating a particular principle, followed by short JSON snippets that are either valid or invalid against that schema. Valid examples are in green, with a checkmark. Invalid examples are in red, with a cross. Often there are comments in between to explain why something is or isn’t valid.

Note

These examples are tested automatically whenever the book is built, so hopefully they are not just helpful, but also correct!

For example, here’s a snippet illustrating how to use the number type:

{ "type": "number" }

42

-1

Simple floating point number:

5.0

Exponential notation also works:

2.99792458e8

Numbers as strings are rejected:

"42"