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JSON Schema to OpenAPI Schema

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


  • 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
  • converts dependencies to an allOf + oneOf OpenAPI-valid equivalent


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


Here's a small example to get the idea:

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

const schema = {
  '$schema': '',
  type: ['string', 'null'],
  format: 'date-time',

const convertedSchema = toOpenApi(schema);


The example prints out

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

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


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.


OpenAPI is often described as an extension of JSON Schema, but both specs have changed over time and grown independently. OpenAPI v2 was based on JSON Schema draft v4 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.

Diagram showing data model (the objects, payload bodies, etc) and service model (endpoints, headers, metadata, etc)

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).


† Draft v5 is also known as Draft Wright 00, as the drafts are often named after the author, and this was the first one by A. Wright. Amongst other things, draft v5 aimed to rewrite the meta files, but the experiment failed, meaning we need to continue to use the draft v4 metafiles. Ugh.


Converting Back

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


To run the test-suite:

npm test