Migrating from Draft 03 to Draft 04

Introduction

The migration from Draft 3 to Draft 4 of JSON Schema introduces changes in how schemas are defined and validated. Draft 4, published on January 31, 2013, introduced new keywords and revised the behaviours of existing ones.

This guide will help you adapt your JSON Schemas to align with Draft 4 requirements, covering keyword changes, updates, and behavioural modifications.

Keyword changelog

Below is a summary table highlighting keyword changes between Draft 3 and Draft 4.

Helpful notes for Keyword changelog

1. type

In Draft-03, the type keyword could hold a simple value like "string" or "number" and an entire schema as its value.

For example:

data

{ "type": { "type": "array", "items": { "type": "string" } }}

This feature was in Draft-03 but changed in later versions of JSON Schema, where type is limited to simpler values like strings or arrays of strings.

The allOf keyword has now replaced the previous type schema functionality.

Note

Starting with Draft 4, schema identifiers that use an empty URI "" or a fragment-only URI "#" are no longer allowed.

In Draft 3, these identifiers were considered valid:

1id: ""
2id: "#"
3

However, this format is now prohibited from Draft 4 onwards.

Note

Before Draft 3, the JSON Schema only included the Core specification, which outlined the foundational elements for schema structure. With Draft 4, the specification expanded to incorporate Validation, establishing rules for data format, structure, and type requirements. This addition enabled schema authors to define and enforce validation constraints directly within their schemas, making it easier for implementers to ensure data integrity and compatibility as schemas evolved.

Tutorial

This tutorial walks you through key steps and considerations to help you successfully migrate your JSON schemas from Draft 3 to Draft 4.

Step 1: Review Core Changes

Start by familiarizing yourself with the updates in the Draft 4 Core schema specification. Note the revised type, required, and dependencies keywords, which might affect your schemas if you rely on polymorphic types or cross-schema references.

Step 2: Update Validation Keywords

Draft 4 has introduced new keywords such as oneOf, not, anyOf, and allOf. Review each of these additions, and update your schemas to use these keywords if relevant. For instance:

• If you have properties that must always be present, use required to define these properties explicitly.
• For schemas that contain nested dependencies, consider restructuring them using dependencies to improve schema maintainability.

Validate and test your updated schemas manually, or with your preferred tool.