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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:

In Python, JSON can be read using the json module in the standard library.
In Ruby, JSON can be read using the json gem.
For C, you may want to consider using Jansson to read and write JSON.


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.


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" }

Simple floating point number:


Exponential notation also works:


Numbers as strings are rejected: