OpenAPI Schema to JSON Schema

A little NodeJS package to convert JSON Schema to OpenAPI Schema Objects.

• From: JSON Schema Draft v5
• To: OpenAPI 3.0

Why?

OpenAPI is often described as an extension of JSON Schema, but both specs have changed over time and grown independently. OpenAPI v2 based based on JSON Schema draft 4 with a long list of deviations, but OpenAPI v3 shrank that list, upping their support to draft v4 and making the list of discrepancies shorter. Despite OpenAPI v3 closing the gap, the issue of JSON Schema divergence has not been resolved fully.

Carefully writing JSON Schema for your data model kiiiinda works, but it is possible to write JSON Schema that creates invalid OpenAPI, and vice versa. For more on this, read the article OpenAPI and JSON Schema Divergence.

This tool sets out to allow folks to convert from JSON Schema (their one source of truth for everything) to OpenAPI (a thing for HTML docs and making SDKs).

Converting Back

To convert the other way, check out openapi-schema-to-json-schema, which this package was based on.

Features

• converts JSON Schema Draft 00 Wright (a.k.a draft v5) to OpenAPI 3.0 Schema Object
• switches type: ['foo', 'null'] to type: foo and nullable: true
• supports deep structures with nested allOfs etc.
• switches patternProperties to x-patternProperties in the Schema Object

NOTE: $refs are not dereferenced. Use a dereferencer such as json-schema-ref-parser prior to using this package.

Installation

npm install --save json-schema-to-openapi-schema

Usage

Here's a small example to get the idea:

const toOpenApi = require('json-schema-to-openapi-schema');

const schema = {
  '$schema': 'http://json-schema.org/draft-04/schema#',
  type: ['string', 'null'],
  format: 'date-time',
};

const convertedSchema = toOpenApi(schema);

console.log(convertedSchema);

The example prints out

{
  type: 'string',
  format: 'date-time',
  nullable: true
}

Options

The function accepts options object as the second argument.

cloneSchema (boolean)

If set to false, converts the provided schema in place. If true, clones the schema by converting it to JSON and back. The overhead of the cloning is usually negligible. Defaults to true.