zod-openapi

zod-openapi

A Typescript library to use Zod Schemas to create OpenAPI v3.x documentation

Install

Install via npm, yarn or pnpm:

npm install zod zod-openapi
## or
yarn add zod zod-openapi
## or
pnpm install zod zod-openapi

Usage

Extend Zod

This mutates Zod to add an extra .openapi() method. Call this at the top of your entry point(s). You can achieve this in two different ways, depending on your preference.

Subpath Import

import 'zod-openapi/extend';
import { z } from 'zod';

z.string().openapi({ description: 'hello world!', example: 'hello world' });

Manual Extension

This is useful if you have a specific instance of Zod or a Zod instance from another library that you would like to target.

import { z } from 'zod';
import { extendZodWithOpenApi } from 'zod-openapi';

extendZodWithOpenApi(z);

z.string().openapi({ description: 'hello world!', example: 'hello world' });

.openapi()

Use the .openapi() method to add metadata to a specific Zod type. The .openapi() method takes an object with the following options:

Option	Description
OpenAPI Options	This will take any option you would put on a SchemaObject.
effectType	Use to override the creation type for a Zod Effect
header	Use to provide metadata for response headers
param	Use to provide metadata for request parameters
ref	Use this to auto register a schema as a re-usable component
refType	Use this to set the creation type for a component which is not referenced in the document.
type	Use this to override the generated type. If this is provided no metadata will be generated.
unionOneOf	Set to true to force a single ZodUnion to output oneOf instead of anyOf. See CreateDocumentOptions for a global option

createDocument

Creates an OpenAPI documentation object

import 'zod-openapi/extend';
import { z } from 'zod';
import { createDocument } from 'zod-openapi';

const jobId = z.string().openapi({
  description: 'A unique identifier for a job',
  example: '12345',
  ref: 'jobId',
});

const title = z.string().openapi({
  description: 'Job title',
  example: 'My job',
});

const document = createDocument({
  openapi: '3.1.0',
  info: {
    title: 'My API',
    version: '1.0.0',
  },
  paths: {
    '/jobs/{jobId}': {
      put: {
        requestParams: { path: z.object({ jobId }) },
        requestBody: {
          content: {
            'application/json': { schema: z.object({ title }) },
          },
        },
        responses: {
          '200': {
            description: '200 OK',
            content: {
              'application/json': { schema: z.object({ jobId, title }) },
            },
          },
        },
      },
    },
  },
});

Creates the following object:

{
  "openapi": "3.1.0",
  "info": {
    "title": "My API",
    "version": "1.0.0"
  },
  "paths": {
    "/jobs/{jobId}": {
      "put": {
        "parameters": [
          {
            "in": "path",
            "name": "jobId",
            "description": "A unique identifier for a job",
            "schema": {
              "$ref": "#/components/schemas/jobId"
            }
          }
        ],
        "requestBody": {
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "properties": {
                  "title": {
                    "type": "string",
                    "description": "Job title",
                    "example": "My job"
                  }
                },
                "required": ["title"]
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "200 OK",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "jobId": {
                      "$ref": "#/components/schemas/jobId"
                    },
                    "title": {
                      "type": "string",
                      "description": "Job title",
                      "example": "My job"
                    }
                  },
                  "required": ["jobId", "title"]
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "jobId": {
        "type": "string",
        "description": "A unique identifier for a job",
        "example": "12345"
      }
    }
  }
}

CreateDocumentOptions

createDocument takes an optional CreateDocumentOptions argument which can be used to modify how the document is created.

const document = createDocument(details, {
  defaultDateSchema: { type: 'string', format: 'date-time' }, // defaults to { type: 'string' }
  unionOneOf: true, // defaults to false. Forces all ZodUnions to output oneOf instead of anyOf. An `.openapi()` `unionOneOf` value takes precedence over this one.
  enforceDiscriminatedUnionComponents: true, // defaults to false. Throws an error if a Discriminated Union member is not registered as a component.
});

createSchema

Creates an OpenAPI Schema Object along with any registered components. OpenAPI 3.1.0 Schema Objects are fully compatible with JSON Schema.

import 'zod-openapi/extend';
import { z } from 'zod';
import { createSchema } from 'zod-openapi';

const jobId = z.string().openapi({
  description: 'A unique identifier for a job',
  example: '12345',
  ref: 'jobId',
});

const title = z.string().openapi({
  description: 'Job title',
  example: 'My job',
});

const job = z.object({
  jobId,
  title,
});

const { schema, components } = createSchema(job);

Creates the following object:

{
  "schema": {
    "type": "object",
    "properties": {
      "jobId": {
        "$ref": "#/components/schemas/jobId"
      },
      "title": {
        "type": "string",
        "description": "Job title",
        "example": "My job"
      }
    },
    "required": ["jobId", "title"]
  },
  "components": {
    "jobId": {
      "type": "string",
      "description": "A unique identifier for a job",
      "example": "12345"
    }
  }
}

CreateSchemaOptions

createSchema takes an optional CreateSchemaOptions parameter which can also take the same options as CreateDocumentOptions along with the following options:

const { schema, components } = createSchema(job, {
  schemaType: 'input'; // This controls whether this should be rendered as a request (`input`) or response (`output`). Defaults to `output`
  openapi: '3.0.0'; // OpenAPI version to use, defaults to `'3.1.0'`
  components: { jobId: z.string() } // Additional components to use and create while rendering the schema
  componentRefPath: '#/definitions/' // Defaults to #/components/schemas/
})

Request Parameters

Query, Path, Header & Cookie parameters can be created using the requestParams key under the method key as follows:

createDocument({
  paths: {
    '/jobs/{a}': {
      put: {
        requestParams: {
          path: z.object({ a: z.string() }),
          query: z.object({ b: z.string() }),
          cookie: z.object({ cookie: z.string() }),
          header: z.object({ 'custom-header': z.string() }),
        },
      },
    },
  },
});

If you would like to declare parameters in a more traditional way you may also declare them using the parameters key. The definitions will then all be combined.

createDocument({
  paths: {
    '/jobs/{a}': {
      put: {
        parameters: [
          z.string().openapi({
            param: {
              name: 'job-header',
              in: 'header',
            },
          }),
        ],
      },
    },
  },
});

Request Body

Where you would normally declare the media type, set the schema as your Zod Schema as follows.

createDocument({
  paths: {
    '/jobs': {
      get: {
        requestBody: {
          content: {
            'application/json': { schema: z.object({ a: z.string() }) },
          },
        },
      },
    },
  },
});

If you wish to use OpenAPI syntax for your schemas, simply add an OpenAPI schema to the schema field instead.

Responses

Similarly to the Request Body, simply set the schema as your Zod Schema as follows. You can set the response headers using the headers key.

createDocument({
  paths: {
    '/jobs': {
      get: {
        responses: {
          200: {
            description: '200 OK',
            content: {
              'application/json': { schema: z.object({ a: z.string() }) },
            },
            headers: z.object({
              'header-key': z.string(),
            }),
          },
        },
      },
    },
  },
});

Callbacks

createDocument({
  paths: {
    '/jobs': {
      get: {
        callbacks: {
          onData: {
            '{$request.query.callbackUrl}/data': {
              post: {
                requestBody: {
                  content: {
                    'application/json': { schema: z.object({ a: z.string() }) },
                  },
                },
                responses: {
                  200: {
                    description: '200 OK',
                    content: {
                      'application/json': {
                        schema: z.object({ a: z.string() }),
                      },
                    },
                  },
                },
              },
            },
          },
        },
      },
    },
  },
});

Creating Components

OpenAPI allows you to define reusable components and this library allows you to replicate that in two separate ways.

1. Auto registering schema
2. Manually registering schema

Schema

If we take the example in createDocument and instead create title as follows

Auto Registering Schema

const title = z.string().openapi({
  description: 'Job title',
  example: 'My job',
  ref: 'jobTitle', // <- new field
});

Wherever title is used in schemas across the document, it will instead be created as a reference.

{ "$ref": "#/components/schemas/jobTitle" }

title will then be outputted as a schema within the components section of the documentation.

{
  "components": {
    "schemas": {
      "jobTitle": {
        "type": "string",
        "description": "Job title",
        "example": "My job"
      }
    }
  }
}

This is a great way to create less repetitive Open API documentation. There are some Open API features like discriminator mapping which require all schemas in the union to contain a ref.

Manually Registering Schema

Another way to register schema instead of adding a ref is to add it to the components directly. This will still work in the same way as ref. So whenever we run into that Zod type we will replace it with a reference.

eg.

createDocument({
  components: {
    schemas: {
      jobTitle: title, // this will register this Zod Schema as jobTitle unless `ref` in `.openapi()` is specified on the type
    },
  },
});

Unfortunately, as a limitation of this library, you will need to attach an .openapi() field or .describe() to the schema that you are passing into the components or you will not reap the full benefits of component generation. As a result, I recommend utilising the auto registering components over manual registration.

Parameters

Query, Path, Header & Cookie parameters can be similarly registered:

// Easy auto registration
const jobId = z.string().openapi({
  description: 'Job ID',
  example: '1234',
  param: { ref: 'jobRef' },
});

createDocument({
  paths: {
    '/jobs/{jobId}': {
      put: {
        requestParams: {
          header: z.object({
            jobId,
          }),
        },
      },
    },
  },
});

// or more verbose auto registration
const jobId = z.string().openapi({
  description: 'Job ID',
  example: '1234',
  param: { in: 'header', name: 'jobId', ref: 'jobRef' },
});

createDocument({
  paths: {
    '/jobs/{jobId}': {
      put: {
        parameters: [jobId],
      },
    },
  },
});

// or manual registeration
const otherJobId = z.string().openapi({
  description: 'Job ID',
  example: '1234',
  param: { in: 'header', name: 'jobId' },
});

createDocument({
  components: {
    parameters: {
      jobRef: jobId,
    },
  },
});

Response Headers

Response headers can be similarly registered:

const header = z.string().openapi({
  description: 'Job ID',
  example: '1234',
  header: { ref: 'some-header' },
});

// or

const jobIdHeader = z.string().openapi({
  description: 'Job ID',
  example: '1234',
});

createDocument({
  components: {
    headers: {
      someHeaderRef: jobIdHeader,
    },
  },
});

Responses

Entire Responses can also be registered

const response: ZodOpenApiResponseObject = {
  description: '200 OK',
  content: {
    'application/json': {
      schema: z.object({ a: z.string() }),
    },
  },
  ref: 'some-response',
};

//or

const response: ZodOpenApiResponseObject = {
  description: '200 OK',
  content: {
    'application/json': {
      schema: z.object({ a: z.string() }),
    },
  },
};

createDocument({
  components: {
    responses: {
      'some-response': response,
    },
  },
});

Callbacks

Callbacks can also be registered

const callback: ZodOpenApiCallbackObject = {
  ref: 'some-callback'
  post: {
    responses: {
      200: {
        description: '200 OK',
        content: {
          'application/json': {
            schema: z.object({ a: z.string() }),
          },
        },
      },
    },
  },
};

//or

const callback: ZodOpenApiCallbackObject = {
  post: {
    responses: {
      200: {
        description: '200 OK',
        content: {
          'application/json': {
            schema: z.object({ a: z.string() }),
          },
        },
      },
    },
  },
};

createDocument({
  components: {
    callbacks: {
      'some-callback': callback,
    },
  },
});

Zod Effects

.transform(), .catch(), .default() and .pipe() are complicated because they all comprise of two different types that we could generate (input & output).

We attempt to determine what type of schema to create based on the following contexts:

Input: Request Bodies, Request Parameters, Headers

Output: Responses, Response Headers

As an example:

z.object({
  a: z.string().default('a'),
});

In a request context, this would render the following OpenAPI schema:

type: 'object'
properties:
  - a:
    type: 'string'
    default: 'a'

or the following for a response:

type: 'object'
properties:
  - a:
    type: 'string'
    default: 'a'
required:
  - a

Note how the response schema created an extra required field. This means, if you were to register a Zod schema with .default() as a component and use it in both a request or response, your schema would be invalid. Zod OpenAPI keeps track of this usage and will throw an error if this occurs.

EffectType

z.string().transform((str) => str.trim());

Whilst the TypeScript compiler can understand that the result is still a string, unfortunately we cannot introspect this as your transform function may be far more complicated than this example. To address this, you can set the effectType on the schema to same, input or output.

same - This informs Zod OpenAPI to pick either the input schema or output schema to generate with because they should be the same.

z.string()
  .transform((str) => str.trim())
  .openapi({ effectType: 'same' });

If the transform were to drift from this, you will receive a TypeScript error:

z.string()
  .transform((str) => str.length)
  .openapi({ effectType: 'same' });
//           ~~~~~~~~~~
//           Type 'same' is not assignable to type 'CreationType | undefined'.ts(2322)

input or output - This tells Zod OpenAPI to pick a specific schema to create whenever we run into this schema, regardless of it is a request or response schema.

z.string()
  .transform((str) => str.length)
  .openapi({ effectType: 'input' });

Preprocess

.preprocess() will always return the output type even if we are creating an input schema. If a different input type is required you can achieve this with a .transform() combined with a .pipe() or simply declare a manual type in .openapi().

Component Effects

If you are adding a ZodSchema directly to the components section which is not referenced anywhere in the document, additional context may be required to create either an input or output schema. You can do this by setting the refType field to input or output in .openapi(). This defaults to output by default.

Supported OpenAPI Versions

Currently the following versions of OpenAPI are supported

• 3.0.0
• 3.0.1
• 3.0.2
• 3.0.3
• 3.1.0

Setting the openapi field will change how the some of the components are rendered.

createDocument({
  openapi: '3.1.0',
});

As an example z.string().nullable() will be rendered differently

3.0.0

{
  "type": "string",
  "nullable": true
}

3.1.0

{
  "type": ["string", "null"]
}

Supported Zod Schema

• ZodAny
• ZodArray
  • minItems/maxItems mapping for .length(), .min(), .max()
• ZodBigInt
  • integer type and int64 format mapping
• ZodBoolean
• ZodBranded
• ZodCatch
  • Treated as ZodDefault
• ZodCustom
• ZodDate
  • type is mapped as string by default
• ZodDefault
• ZodDiscriminatedUnion
  • discriminator mapping when all schemas in the union are registered. The discriminator must be a ZodLiteral, ZodEnum or ZodNativeEnum with string values. Only values wrapped in ZodBranded, ZodReadOnly and ZodCatch are supported.
• ZodEffects
  • transform support for request schemas. See Zod Effects for how to enable response schema support
  • pre-process support. We assume that the input type is the same as the output type. Otherwise pipe and transform can be used instead.
  • refine full support
• ZodEnum
• ZodIntersection
• ZodLazy
  • The recursive schema within the ZodLazy or the ZodLazy must be registered as a component. See Creating Components for more information.
• ZodLiteral
• ZodNativeEnum
  • supporting string, number and combined enums.
• ZodNever
• ZodNull
• ZodNullable
• ZodNumber
  • integer type mapping for .int()
  • exclusiveMin/min/exclusiveMax/max mapping for .min(), .max(), lt(), gt(), .positive(), .negative(), .nonnegative(), .nonpositive().
  • multipleOf mapping for .multipleOf()
• ZodObject
  • additionalProperties mapping for .catchall(), .strict()
  • allOf mapping for .extend() when the base object is registered and does not have catchall(), strict() and extension does not override a field.
• ZodOptional
• ZodPipeline
  • See Zod Effects for more information.
• ZodReadonly
• ZodRecord
• ZodSet
  • Treated as an array with uniqueItems (you may need to add a pre-process to convert it to a set)
• ZodString
  • format mapping for .url(), .uuid(), .email(), .datetime(), .date(), .time(), .duration(), .ip({ version: 'v4' }), .ip({ version: 'v6' }), .cidr({ version: 'v4' }), .cidr({ version: 'v6' })
  • minLength/maxLength mapping for .length(), .min(), .max()
  • pattern mapping for .regex(), .startsWith(), .endsWith(), .includes()
  • contentEncoding mapping for .base64() for OpenAPI 3.1.0+
• ZodTuple
  • items mapping for .rest()
  • prefixItems mapping for OpenAPI 3.1.0+
• ZodUndefined
• ZodUnion
  • By default it outputs an anyOf schema. Use unionOneOf to change this to output oneOf instead.
• ZodUnknown

If this library cannot determine a type for a Zod Schema, it will throw an error. To avoid this, declare a manual type in the .openapi() section of that schema.

eg.

z.custom().openapi({ type: 'string' });

Examples

See the library in use in the examples folder.

• Simple - setup | openapi.yml | redoc documentation

Ecosystem

• fastify-zod-openapi - Fastify plugin for zod-openapi. This includes type provider, Zod schema validation, Zod schema serialization and Swagger UI support.

• eslint-plugin-zod-openapi - Eslint rules for zod-openapi. This includes features which can autogenerate Typescript comments for your Zod types based on your description, example and deprecated fields.

Comparisons

@asteasolutions/zod-to-openapi

Development

Prerequisites

• Node.js LTS
• pnpm

pnpm
pnpm build

Test

pnpm test

Lint

# Fix issues
pnpm format

# Check for issues
pnpm lint

Release

To release a new version

1. Create a new GitHub Release
2. Select 🏷️ Choose a tag, enter a version number. eg. v1.2.0 and click + Create new tag: vX.X.X on publish.
3. Click the Generate release notes button and adjust the description.
4. Tick the Set as the latest release box and click Publish release. This will trigger the Release workflow.
5. Check the Pull Requests tab for a PR labelled Release vX.X.X.
6. Click Merge Pull Request on that Pull Request to update master with the new package version.

To release a new beta version

1. Create a new GitHub Release
2. Select 🏷️ Choose a tag, enter a version number with a -beta.X suffix eg. v1.2.0-beta.1 and click + Create new tag: vX.X.X-beta.X on publish.
3. Click the Generate release notes button and adjust the description.
4. Tick the Set as a pre-release box and click Publish release. This will trigger the Prerelease workflow.