@fastify/swagger

A Fastify plugin for serving Swagger (OpenAPI v2) or OpenAPI v3 schemas, which are automatically generated from your route schemas, or from an existing Swagger/OpenAPI schema.

If you are looking for a plugin to generate routes from an existing OpenAPI schema, check out fastify-openapi-glue.

Following plugins serve Swagger/OpenAPI front-ends based on the swagger definitions generated by this plugin:

• @fastify/swagger-ui
• @scalar/fastify-api-reference

See also the migration guide for migrating from @fastify/swagger version <= <=7.x to version >=8.x.

Install

npm i @fastify/swagger

Compatibility

Plugin version	Fastify version
^9.x	^5.x
^8.x	^4.x
^7.x	^4.x
^6.x	^3.x
^3.x	^2.x
^1.x	^1.x

Please note that if a Fastify version is out of support, then so are the corresponding version(s) of this plugin in the table above. See Fastify's LTS policy for more details.

Usage

Add it to your project with register, pass it some options, call the swagger API, and you are done! Below an example of how to configure the OpenAPI v3 specification with Fastify Swagger:

const fastify = require('fastify')()

await fastify.register(require('@fastify/swagger'), {
  openapi: {
    openapi: '3.0.0',
    info: {
      title: 'Test swagger',
      description: 'Testing the Fastify swagger API',
      version: '0.1.0'
    },
    servers: [
      {
        url: 'http://localhost:3000',
        description: 'Development server'
      }
    ],
    tags: [
      { name: 'user', description: 'User related end-points' },
      { name: 'code', description: 'Code related end-points' }
    ],
    components: {
      securitySchemes: {
        apiKey: {
          type: 'apiKey',
          name: 'apiKey',
          in: 'header'
        }
      }
    },
    externalDocs: {
      url: 'https://swagger.io',
      description: 'Find more info here'
    }
  }
})

fastify.put('/some-route/:id', {
  schema: {
    description: 'post some data',
    tags: ['user', 'code'],
    summary: 'qwerty',
    security: [{ apiKey: [] }],
    params: {
      type: 'object',
      properties: {
        id: {
          type: 'string',
          description: 'user id'
        }
      }
    },
    body: {
      type: 'object',
      properties: {
        hello: { type: 'string' },
        obj: {
          type: 'object',
          properties: {
            some: { type: 'string' }
          }
        }
      }
    },
    response: {
      201: {
        description: 'Successful response',
        type: 'object',
        properties: {
          hello: { type: 'string' }
        }
      },
      default: {
        description: 'Default response',
        type: 'object',
        properties: {
          foo: { type: 'string' }
        }
      }
    }
  }
}, (req, reply) => { })

await fastify.ready()
fastify.swagger()

With @fastify/autoload

You need to register @fastify/swagger before registering routes.

const fastify = require('fastify')()
const fastify = fastify()
await fastify.register(require('@fastify/swagger'))
fastify.register(require("@fastify/autoload"), {
  dir: path.join(__dirname, 'routes')
})
await fastify.ready()
fastify.swagger()

API

Register options

Modes

@fastify/swagger supports two registration modes dynamic and static:

Dynamic

dynamic is the default mode, if you use @fastify/swagger this way API schemas will be auto-generated from route schemas:

// All of the below parameters are optional but are included for demonstration purposes
{
  // swagger 2.0 options
  swagger: {
    info: {
      title: String,
      description: String,
      version: String
    },
    externalDocs: Object,
    host: String,
    schemes: [ String ],
    consumes: [ String ],
    produces: [ String ],
    tags: [ Object ],
    securityDefinitions: Object
  },
  // openapi 3.0.3 options
  // openapi: {
  //   info: {
  //     title: String,
  //     description: String,
  //     version: String,
  //   },
  //   externalDocs: Object,
  //   servers: [ Object ],
  //   components: Object,
  //   security: [ Object ],
  //   tags: [ Object ]
  // }
}

All properties detailed in the Swagger (OpenAPI v2) and OpenAPI v3 specifications can be used. @fastify/swagger will generate API schemas that adhere to the Swagger specification by default. If provided an openapi option it will generate OpenAPI compliant API schemas instead.

Examples of using @fastify/swagger in dynamic mode:

• Using the swagger option
• Using the openapi option

Static

static mode must be configured explicitly. In this mode @fastify/swagger serves an already existing Swagger or OpenAPI schema that is passed to it in specification.path:

{
  mode: 'static',
  specification: {
    path: './examples/example-static-specification.yaml',
    postProcessor: function(swaggerObject) {
      return swaggerObject
    },
    baseDir: '/path/to/external/spec/files/location',
  },
}

The specification.postProcessor parameter is optional. It allows you to change your Swagger object on the fly (for example - based on the environment). It accepts swaggerObject - a JavaScript object that was parsed from your yaml or json file and should return a Swagger schema object.

specification.baseDir allows specifying the directory where all spec files that are included in the main one using $ref will be located. By default, this is the directory where the main spec file is located. Provided value should be an absolute path without trailing slash.

An example of using @fastify/swagger with static mode enabled can be found here.

Options

Option	Default	Description
hiddenTag	X-HIDDEN	Tag to control hiding of routes.
hideUntagged	false	If true remove routes without tags from resulting Swagger/OpenAPI schema file.
initOAuth	{}	Configuration options for Swagger UI initOAuth.
openapi	{}	OpenAPI configuration.
stripBasePath	true	Strips base path from routes in docs.
swagger	{}	Swagger configuration.
transform	null	Transform method for the route's schema and url. documentation.
transformObject	null	Transform method for the swagger or openapi object before it is rendered. documentation.
refResolver	{}	Option to manage the $refs of your application's schemas. Read the $ref documentation
exposeHeadRoutes	false	Include HEAD routes in the definitions
decorator	'swagger'	Overrides the Fastify decorator. documentation.

Transform

By passing a synchronous transform function you can modify the route's url and schema.

You may also access the openapiObject and swaggerObject

Some possible uses of this are:

• add the hide flag on schema according to your own logic based on url & schema
• altering the route url into something that's more suitable for the api spec
• using different schemas such as Joi and transforming them to standard JSON schemas expected by this plugin
• hiding routes based on version constraints

This option is available in dynamic mode only.

Examples of all the possible uses mentioned:

const convert = require('joi-to-json')

await fastify.register(require('@fastify/swagger'), {
  swagger: { ... },
  transform: ({ schema, url, route, swaggerObject }) => {
    const {
      params,
      body,
      querystring,
      headers,
      response,
      ...transformedSchema
    } = schema
    let transformedUrl = url

    // Transform the schema as you wish with your own custom logic.
    // In this example convert is from 'joi-to-json' lib and converts a Joi based schema to json schema
    if (params) transformedSchema.params = convert(params)
    if (body) transformedSchema.body = convert(body)
    if (querystring) transformedSchema.querystring = convert(querystring)
    if (headers) transformedSchema.headers = convert(headers)
    if (response) transformedSchema.response = convert(response)

    // can add the hide tag if needed
    if (url.startsWith('/internal')) transformedSchema.hide = true

    // can transform the url
    if (url.startsWith('/latest_version/endpoint')) transformedUrl = url.replace('latest_version', 'v3')

    // can add the hide tag for routes that do not match the swaggerObject version
    if (route?.constraints?.version !== swaggerObject.swagger) transformedSchema.hide = true

    return { schema: transformedSchema, url: transformedUrl }
  }
})

You can also attach the transform function on a specific endpoint:

fastify.get("/", {
  schema: { ... },
  config: {
    swaggerTransform: ({ schema, url, route, swaggerObject }) => { ... }
  }
})

If both a global and a local transform function is available for an endpoint, the endpoint-specific transform function will be used.

The local transform function can be useful if you:

• want to add additional information to a specific endpoint
• have an endpoint which requires different transformation from other endpoints
• want to entirely ignore the global transform function for one endpoint

The endpoint-specific transform can be used to "disable" the global transform function by passing in false instead of a function.

Transform Object

By passing a synchronous transformObject function you can modify the resulting swaggerObject or openapiObject before it is rendered.

await fastify.register(require('@fastify/swagger'), {
  swagger: { ... },
  transformObject ({ swaggerObject }) => {
    swaggerObject.info.title = 'Transformed';
    return swaggerObject;
  }
})

Managing your $refs

When this plugin is configured as dynamic mode, it will resolve all $refs in your application's schemas. This process will create an new in-line schema that is going to reference itself.

This logic step is done to make sure that the generated documentation is valid, otherwise the Swagger UI will try to fetch the schemas from the server or the network and fail.

By default, this option will resolve all $refs renaming them to def-${counter}, but your view models keep the original $id naming thanks to the title parameter.

To customize this logic you can pass a refResolver option to the plugin:

await fastify.register(require('@fastify/swagger'), {
  swagger: { ... },
  ...
  refResolver: {
    buildLocalReference (json, baseUri, fragment, i) {
      return json.$id || `my-fragment-${i}`
    }
  }
}

To deep down the buildLocalReference arguments, you may read the documentation.

Decorator

By passing a string to the decorator option, you can override the default decorator function (fastify.swagger()) with a custom one. This allows you to create multiple documents by registering @fastify/swagger multiple times with different transform functions:

// Create an internal Swagger doc
await fastify.register(require('@fastify/swagger'), {
  swagger: { ... },
  transform: ({ schema, url, route, swaggerObject }) => {
    const {
      params,
      body,
      querystring,
      headers,
      response,
      ...transformedSchema
    } = schema
    let transformedUrl = URL

    // Hide external URLs
    if (url.startsWith('/external')) transformedSchema.hide = true

    return { schema: transformedSchema, url: transformedUrl }
  },
  decorator: 'internalSwagger'
})

// Create an external Swagger doc
await fastify.register(require('@fastify/swagger'), {
  swagger: { ... },
  transform: ({ schema, url, route, swaggerObject }) => {
    const {
      params,
      body,
      querystring,
      headers,
      response,
      ...transformedSchema
    } = schema
    let transformedUrl = URL

    // Hide internal URLs
    if (url.startsWith('/internal')) transformedSchema.hide = true

    return { schema: transformedSchema, url: transformedUrl }
  },
  decorator: 'externalSwagger'
})

You can then call those decorators individually to retrieve them:

fastify.internalSwagger()
fastify.externalSwagger()

Route options

It is possible to instruct @fastify/swagger to include specific HEAD routes in the definitions by adding exposeHeadRoute in the route config, like so:

  fastify.get('/with-head', {
    schema: {
      operationId: 'with-head',
      response: {
        200: {
          description: 'Expected Response',
          type: 'object',
          properties: {
            foo: { type: 'string' }
          }
        }
      }
    },
    config: {
      swagger: {
        exposeHeadRoute: true,
      }
    }
  }, () => {})

Response Options

Response description and response body description

description is a required field as per the Swagger specification. If it is not provided then the plugin will automatically generate one with the value 'Default Response'. If you supply a description it will be used for both the response and response body schema, for example:

fastify.get('/description', {
  schema: {
    response: {
      200: {
        description: 'response and schema description',
        type: 'string'
      }
    }
  }
}, () => {})

Generates this in a Swagger (OpenAPI v2) schema's paths:

{
  "/description": {
    "get": {
      "responses": {
        "200": {
          "description": "response and schema description",
          "schema": {
            "description": "response and schema description",
            "type": "string"
          }
        }
      }
    }
  }
}

And this in a OpenAPI v3 schema's paths:

{
  "/description": {
    "get": {
      "responses": {
        "200": {
          "description": "response and schema description",
          "content": {
            "application/json": {
              "schema": {
                "description": "response and schema description",
                "type": "string"
              }
            }
          }
        }
      }
    }
  }
}

If you want to provide different descriptions for the response and response body, use the x-response-description field alongside description:

fastify.get('/responseDescription', {
  schema: {
    response: {
      200: {
        'x-response-description': 'response description',
        description: 'schema description',
        type: 'string'
      }
    }
  }
}, () => {})

Additionally, if you provide a $ref in your response schema but no description, the reference's description will be used as a fallback. Note that at the moment, $ref will only be resolved by matching with $id and not through complex paths.

Status code 2xx

Fastify supports both the 2xx and 3xx status codes, however Swagger (OpenAPI v2) itself does not. @fastify/swagger transforms 2xx status codes into 200, but will omit it if a 200 status code has already been declared. OpenAPI v3 supports the 2xx syntax so is unaffected.

Example:

{
  response: {
    '2xx': {
      description: '2xx',
      type: 'object'
    }
  }
}

// will become
{
  response: {
    200: {
      schema: {
        description: '2xx',
        type: 'object'
      }
    }
  }
}

Response headers

You can decorate your own response headers by following the below example:

{
  response: {
    200: {
      type: 'object',
      headers: {
        'X-Foo': {
          type: 'string'
        }
      }
    }
  }
}

Note: You need to specify type property when you decorate the response headers, otherwise the schema will be modified by Fastify.

Different content types responses

Note: not supported by Swagger (OpenAPI v2), only OpenAPI v3 Different content types responses are supported by @fastify/swagger and @fastify. Please use content for the response otherwise Fastify itself will fail to compile the schema:

{
  response: {
    200: {
      description: 'Description and all status-code based properties are working',
      content: {
        'application/json': {
          schema: {
            name: { type: 'string' },
            image: { type: 'string' },
            address: { type: 'string' }
          }
        },
        'application/vnd.v1+json': {
          schema: {
            fullName: { type: 'string' },
            phone: { type: 'string' }
          }
        }
      }
    }
  }
}

Empty Body Responses

Empty body responses are supported by @fastify/swagger. Please specify type: 'null' for the response otherwise Fastify itself will fail to compile the schema:

{
  response: {
    204: {
      type: 'null',
      description: 'No Content'
    },
    503: {
      type: 'null',
      description: 'Service Unavailable'
    }
  }
}

OpenAPI Parameter Options

Note: OpenAPI's terminology differs from Fastify's. OpenAPI uses "parameter" to refer to parts of a request that in Fastify's validation documentation are called "querystring", "params", and "headers".

OpenAPI provides some options beyond those provided by the JSON schema specification for specifying the shape of parameters. A prime example of this is the collectionFormat option for specifying how to encode parameters that should be handled as arrays of values.

These encoding options only change how Swagger UI presents its documentation and how it generates curl commands when the Try it out button is clicked. Depending on which options you set in your schema, you may also need to change the default query string parser used by Fastify so that it produces a JavaScript object that will conform to the schema. As far as arrays are concerned, the default query string parser conforms to the collectionFormat: "multi" specification. If you were to select collectionFormat: "csv", you would have to replace the default query string parser with one that parses CSV parameter values into arrays. The same applies to the other parts of a request that OpenAPI calls "parameters" and which are not encoded as JSON in a request.

You can also apply different serialization style and explode as specified here.

@fastify/swagger supports these options as shown in this example:

// Need to add a collectionFormat keyword to ajv in fastify instance
const fastify = Fastify({
  ajv: {
    customOptions: {
      keywords: ['collectionFormat']
    }
  }
})

fastify.route({
  method: 'GET',
  url: '/',
  schema: {
    querystring: {
      type: 'object',
      required: ['fields'],
      additionalProperties: false,
      properties: {
        fields: {
          type: 'array',
          items: {
            type: 'string'
          },
          minItems: 1,
          //
          // Note that this is an OpenAPI version 2 configuration option. The
          // options changed in version 3.
          //
          // Put `collectionFormat` on the same property which you are defining
          // as an array of values. (i.e. `collectionFormat` should be a sibling
          // of the `type: "array"` specification.)
          collectionFormat: 'multi'
        }
      },
     // OpenAPI 3 serialization options
     explode: false,
     style: "deepObject"
    }
  },
  handler (request, reply) {
    reply.send(request.query.fields)
  }
})

There is a complete runnable example here.

Complex serialization in query and cookie, eg. JSON

Note: not supported by Swagger (OpenAPI v2), only OpenAPI v3

http://localhost/?filter={"foo":"baz","bar":"qux"}

IMPORTANT CAVEAT You will need to change the default query string parser used by Fastify so that it produces a JavaScript object that will conform to the schema. See example.

fastify.route({
  method: 'GET',
  url: '/',
  schema: {
    querystring: {
      type: 'object',
      required: ['filter'],
      additionalProperties: false,
      properties: {
        filter: {
          type: 'object',
          required: ['foo'],
          properties: {
            foo: { type: 'string' },
            bar: { type: 'string' }
          },
          'x-consume': 'application/json'
        }
      }
    }
  },
  handler (request, reply) {
    reply.send(request.query.filter)
  }
})

Will generate this in the OpenAPI v3 schema's paths:

{
  "/": {
    "get": {
      "parameters": [
        {
          "in": "query",
          "name": "filter",
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "required": [
                  "foo"
                ],
                "properties": {
                  "foo": {
                    "type": "string"
                  },
                  "bar": {
                    "type": "string"
                  }
                }
              }
            }
          }
        }
      ]
    }
  }
}

Route parameters

Route parameters in Fastify are called params, these are values included in the URL of the requests, for example:

fastify.route({
  method: 'GET',
  url: '/:id',
  schema: {
    params: {
      type: 'object',
      properties: {
        id: {
          type: 'string',
          description: 'user id'
        }
      }
    }
  },
  handler (request, reply) {
    reply.send(request.params.id)
  }
})

Will generate this in the Swagger (OpenAPI v2) schema's paths:

{
  "/{id}": {
    "get": {
      "parameters": [
        {
          "type": "string",
          "description": "user id",
          "required": true,
          "in": "path",
          "name": "id"
        }
      ],
      "responses": {
        "200": {
          "description": "Default Response"
        }
      }
    }
  }
}

Will generate this in the OpenAPI v3 schema's paths:

{
  "/{id}": {
    "get": {
      "parameters": [
        {
          "schema": {
            "type": "string"
          },
          "in": "path",
          "name": "id",
          "required": true,
          "description": "user id"
        }
      ],
      "responses": {
        "200": {
          "description": "Default Response"
        }
      }
    }
  }
}

Whether params is not present in the schema, or a schema is not provided, parameters are automatically generated, for example:

fastify.route({
  method: 'POST',
  url: '/:id',
  handler (request, reply) {
    reply.send(request.params.id)
  }
})

Will generate this in the Swagger (OpenAPI v2) schema's paths:

{
  "/{id}": {
    "get": {
      "parameters": [
        {
          "type": "string",
          "required": true,
          "in": "path",
          "name": "id"
        }
      ],
      "responses": {
        "200": {
          "description": "Default Response"
        }
      }
    }
  }
}

Will generate this in the OpenAPI v3 schema's paths:

{
  "/{id}": {
    "get": {
      "parameters": [
        {
          "schema": {
            "type": "string"
          },
          "in": "path",
          "name": "id",
          "required": true
        }
      ],
      "responses": {
        "200": {
          "description": "Default Response"
        }
      }
    }
  }
}

Links

Note: not supported by Swagger (OpenAPI v2), only OpenAPI v3

OpenAPI v3 Links are added by adding a links property to the top-level options of a route. See:

fastify.get('/user/:id', {
  schema: {
    params: {
      type: 'object',
      properties: {
        id: {
          type: 'string',
          description: 'the user identifier, as userId'
        }
      },
      required: ['id']
    },
    response: {
      200: {
        type: 'object',
        properties: {
          uuid: {
            type: 'string',
            format: 'uuid'
          }
        }
      }
    }
  },
  links: {
    // The status code must match the one in the response
    200: {
      address: {
        // See the OpenAPI documentation
        operationId: 'getUserAddress',
        parameters: {
          id: '$request.path.id'
        }
      }
    }
  }
}, () => {})

fastify.get('/user/:id/address', {
  schema: {
    operationId: 'getUserAddress',
    params: {
      type: 'object',
      properties: {
        id: {
          type: 'string',
          description: 'the user identifier, as userId'
        }
      },
      required: ['id']
    },
    response: {
      200: {
        type: 'string'
      }
    }
  }
}, () => {})

Hide a route

There are two ways to hide a route from the Swagger UI:

• Pass { hide: true } to the schema object inside the route declaration.
• Use the tag declared in hiddenTag options property inside the route declaration. Default is X-HIDDEN.

Swagger function options

Registering @fastify/swagger decorates the fastify instance with fastify.swagger(), which returns a JSON object representing the API. If { yaml: true } is passed to fastify.swagger() it will return a YAML string.

Integration

You can integrate this plugin with @fastify/helmet with some little work.

@fastify/helmet options example:

.register(helmet, instance => {
  return {
    contentSecurityPolicy: {
      directives: {
        ...helmet.contentSecurityPolicy.getDefaultDirectives(),
        "form-action": ["'self'"],
        "img-src": ["'self'", "data:", "validator.swagger.io"],
        "script-src": ["'self'"].concat(instance.swaggerCSP.script),
        "style-src": ["'self'", "https:"].concat(
          instance.swaggerCSP.style
        ),
      }
    }
  }
})

Add examples to the schema

Note: OpenAPI and JSON Schema have different examples field formats.

Array with examples from JSON Schema converted to OpenAPI example or examples field automatically with generated names (example1, example2...):

fastify.route({
  method: 'POST',
  url: '/',
  schema: {
    querystring: {
      type: 'object',
      required: ['filter'],
      properties: {
        filter: {
          type: 'object',
          required: ['foo'],
          properties: {
            foo: { type: 'string' },
            bar: { type: 'string' }
          },
          examples: [
            { foo: 'bar', bar: 'baz' },
            { foo: 'foo', bar: 'bar' }
          ]
        }
      },
      examples: [
        { filter: { foo: 'bar', bar: 'baz' } }
      ]
    }
  },
  handler (request, reply) {
    reply.send(request.query.filter)
  }
})

Will generate this in the OpenAPI v3 schema's path:

"/": {
  "post": {
    "requestBody": {
      "content": {
        "application/json": {
          "schema": {
            "type": "object",
            "required": ["filter"],
            "properties": {
              "filter": {
                "type": "object",
                "required": ["foo"],
                "properties": {
                  "foo": { "type": "string" },
                  "bar": { "type": "string" }
                },
                "example": { "foo": "bar", "bar": "baz" }
              }
            }
          },
          "examples": {
            "example1": {
              "value": { "filter": { "foo": "bar", "bar": "baz" } }
            },
            "example2": {
              "value": { "filter": { "foo": "foo", "bar": "bar" } }
            }
          }
        }
      },
      "required": true
    },
    "responses": { "200": { "description": "Default Response" } }
  }
}

If you want to set your own names or add descriptions to the examples of schemas, you can use x-examples field to set examples in OpenAPI format:

// Need to add a new allowed keyword to ajv in fastify instance
const fastify = Fastify({
  ajv: {
    plugins: [
      function (ajv) {
        ajv.addKeyword({ keyword: 'x-examples' })
      }
    ]
  }
})

fastify.route({
  method: 'POST',
  url: '/feed-animals',
  schema: {
    body: {
      type: 'object',
      required: ['animals'],
      properties: {
        animals: {
          type: 'array',
          items: {
            type: 'string'
          },
          minItems: 1,
        }
      },
      "x-examples": {
        Cats: {
          summary: "Feed cats",
          description:
            "A longer **description** of the options with cats",
          value: {
            animals: ["Tom", "Garfield", "Felix"]
          }
        },
        Dogs: {
          summary: "Feed dogs",
          value: {
            animals: ["Spike", "Odie", "Snoopy"]
          }
        }
      }
    }
  },
  handler (request, reply) {
    reply.send(request.body.animals)
  }
})

$id and $ref usage

Development

In order to start development run:

npm i
npm run prepare

So that swagger-ui static folder will be generated for you.

How it works under the hood

@fastify/static serves swagger-ui static files, then calls /docs/json to get the Swagger file and render it.

How to work with $refs

The /docs/json endpoint in dynamic mode produces a single swagger.json file resolving all your

Acknowledgements

This project is kindly sponsored by:

• nearForm
• LetzDoIt

License

Licensed under MIT.