Programming language: Scala
License: Apache License 2.0
Tags: Misc    
Latest version: v0.10.2

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Swagger API spec generator for Play

A library that generates swagger specs from route files and case class reflection, no code annotation needed.

Principles in this lib

  1. No code pollution (e.g. annotation)
  2. DRY (extract as much information from the code as possible)
  3. When documenting an endpoint, it should be just swagger specification that you need to write. You shall not need to learn another API or spec format.

Which translates to

  1. Write your swagger specification in your routes files as comments (json or yml)
  2. Reference your case classes in your swagger spec and play-swagger will generate definitions
  3. Override anything in either the swagger spec in comment or the base swagger spec file (swagger.yml or swagger.json in your conf)


Day-to-day usage

For installation/get-started see the next section.

A simple example

In a cards.routes which is referenced in routes as

->  /api/cards    cards.Routes

You can write the following swagger spec in comment (This example is in yml, but json is also supported). The comment has to start and end with ###.

If you don't write any comment here the endpoint is still going to be picked up by play-swagger, the parameters will be included but there will not be any response format. This allows newly added endpoints to be automatically included in swagger with some basic information.

 #  summary: create a card 
 #  tags:
 #    - Card Endpoints
 #  responses:
 #    200:
 #      description: success
 #      schema:
 #        $ref: '#/definitions/com.iheart.api.Protocol.CardCreated'
 POST      /users/:profileId/contexts/:contextName/cards       controllers.api.Cards.createCard(profileId: Int, contextName: Option[String])

Note that everything in the comment is just standard swagger definition, and it $refs to a case class CardCreated, which is defined in a Protocol object, and it references another case class Card. Here is the source code:

package com.iheart.api

object Protocol {
  case class CardCreated(card: Card)

  case class Card(id: Int, name: String)

This will generate the path with summary, tags, parameters and a response with schema defined, which comes from the comments and case class reflection. It also recursively generates definitions from your case class.
These schemas assumes that you are using a simple Json.format[CardCreated] to generate the json response out of this class. If not, you will have to write the definition yourself in the base swagger spec and reference it here at the endpoint (give it a different name than the full package name though, play-swagger will try to generate definitions for any $ref that starts with the domain package name).

The result swagger specs will look like:


Get Started

In short you need to add sbt-play-swagger plugin which generates swagger.json on package time, then you just need to have a swagger UI instance to consumer that swagger spec. You can find the setup in the example project as well.

Step 1

For play 2.8, Scala 2.13.x and Scala 2.12.x please use

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.11.0")

⚠️ Support for play versions prior to 2.7 has been discontinued. Past versions may work with past play.

If you need support for past play versions, please contribute via issue or pull request!

※ deprecated For play 2.7, sbt 1.x please use

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.10.7")

※ deprecated For play 2.6, sbt 1.x, Scala 2.12.x and 2.11.x please use (No Longer maintained after 0.10.0)

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.10.0-PLAY2.6")

※ deprecated For play 2.6 and sbt 0.13.x please use a special release (No longer maintained after 0.6.2)

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.6.2-PLAY2.6")

※ deprecated For Play 2.5 (No longer maintained after 0.6.5)

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.6.5") 

※ deprecated For play 2.4 (No longer maintained after 0.6.0)

addSbtPlugin("com.iheart" % "sbt-play-swagger" % "0.6.0-PLAY2.4")

Then enable it for your Play app - in build.sbt add SwaggerPlugin to the root project like

lazy val root = (project in file(".")).enablePlugins(PlayScala, SwaggerPlugin) //enable plugin

Also in build.sbt add domain package names for play-swagger to auto generate swagger definitions for domain classes mentioned in your routes

swaggerDomainNameSpaces := Seq("models")

To be more specific, If you want to use the case class defined in the package something.models in swagger (accessed via #ref:definitions/), add the following in sbt.

swaggerDomainNameSpaces := Seq("something.models")

Additionally, if you want to use other packages (e.g. other.models), you can do so like this.

swaggerDomainNameSpaces := Seq("something.models","other.models")

This plugin adds a sbt task swagger, with which you can generate the swagger.json for testing purpose.

This plugin will generate the swagger.jsonand make it available under path assets/swagger.json on sbt package and sbt run.

Alternatively, you can create a controller that uses play-swagger lib to generate the json and serve it, this way you can manipulate the swagger.json at runtime. See [here](docs/AlternativeSetup.md) for details.

Step 2

Add a base swagger.yml (or swagger.json) to your resources folder (for example, conf folder in the play application). This file needs to provide all the required fields according to swagger spec.


  swagger: "2.0"
    title: "Poweramp API"
    description: "Power your music"
    - application/json
    - application/json

Note that info.version is intentionally left out, playSwagger will automatically fillin the build version of the project. However if the version is set here it will be honored. You can also dynamically generate the version string in build file using the swaggerAPIVersion setting.

Step 3a

Deploy a swagger ui and point to the swagger spec end point at 'assets/swagger.json', or

Step 3b

Alternatively you can use swagger-ui webjar and have you play app serving the swagger ui:

The query parameter url is disabled in 4.1.3 and later versions. (GHSA-qrmm-w75w-3wpx)

libraryDependencies += "org.webjars" % "swagger-ui" % "4.11.1"

Copy the index.html and swagger-initializer.js generated in target/${project}/public/lib/main/swagger-ui/ and modify the js files as follows to create Swagger-UI can be used easily.

window.onload = function() {
  window.ui = SwaggerUIBundle({
    // edit url
    url: "/assets/swagger.json",
    dom_id: '#swagger-ui',
    deepLinking: true,
    presets: [
    plugins: [
    layout: "StandaloneLayout"

For more information: installation.md

The sbt-play-swagger plugin will generate the swagger.json on sbt run or sbt package.


How to contribute

If you have any questions/bug reports, please submit an issue on github. With good unit tests coverage, it's pretty easy to add/modify this library as well. Code contribution are more than welcome. Make sure that your code is tested and submit the pull request!



How to override?

To override any of the automatically generated field, you just need to write the same part in your comment or base swagger spec file.

How to override type mappings?

To override the type mapping used for any type, create a swagger-custom-mappings.yml or swagger-custom-mappings.json in conf and add an array of mappings. Each mapping consists of

  1. type a regex matching the type for which the custom specs is
  2. specAsParameter a list of objects to be used when this type is used by a route path parameter or query string parameter. Being a list of json object allows you to expand a single parameter into multiple ones, but in other cases you just need to provide one json object. If you leave this one an empty array, the parameter with this type will be hidden. You must provide a list here, though.
  3. specAsProperty, a json object to be used when the type is used as a property in a definition. If you leave this one empty, play-swagger will try to use the first element in specAsParameter, please note that although most of the fields are common between the two types of spec, a couple of them aren't.

For example

  - type: java\.time\.LocalDate
      - type: string
        format: date
  - type: java\.time\.Duration
    specAsParameter: []   #this hides the type from query and path parameter
      $ref: "#/definitions/Duration"

The preceding example would result in output for a field with type java.time.LocalDate like this:

"fieldName": {
How to use a custom naming strategy?

To use a custom naming strategies to override your case classes field names, you need to add this to your build.sbt:

//default is 'none', which is your camelCased case class
swaggerNamingStrategy := "snake_case" //snake_case_skip_number, kebab-case, lowercase and UpperCamelCase also available
The spec is missing when built to a docker image using sbt-native-pakcager

@mosche answered this one in #114

It's a bit unfortunate the way the docker plugin redefines stage. However, the solution is pretty simple. Just add:

(stage in Docker) <<= (stage in Docker).dependsOn(swagger)
How to hide an endpoint?

If you don't want an end point to be included, add ### NoDocs ### in front of it e.g.

### NoDocs ###
GET   /docs/swagger-ui/*file        controllers.Assets.at(path:String="/public/lib/swagger-ui", file:String)
Skip entire file

The entire file can be skipped by adding ### SkipFileForDocs ### at the beginning of the routes file.

Alternatively, the routes file can be split into multiple files, so that you can skip practically only a part of the file.


### SkipFileForDocs ###

GET      /api/hidden/a                 controllers.hiddenEndPointA()
GET      /api/hidden/b                 controllers.hiddenEndPointB()
GET      /api/hidden/c                 controllers.hiddenEndPointC()
How to specify body content in a POST endpoint

Body content is specified as a special parameter in swagger. So you need to create a parameter in your swagger spec comment as "body", for example

#  parameters:
#    - name: body
#      schema:
#        $ref: '#/definitions/com.iheart.api.Track'
POST   /tracks       controller.Api.createTrack()

Again, play-swagger will generate the definition for com.iheart.api.Track case class

How do I use a different "host" for different environment?

Use the [alternative setup](docs/AlternativeSetup.md). The library returns play JsObject, you can change however you want like

val spec: Try[JsObject] = ps.generate().map(_ + ("host" -> JsString(myHost)))
How to use a route file different from the default "routes"?

In build.sbt, add

swaggerRoutesFile := "my-routes"

or if you took the [alternative setup](docs/AlternativeSetup.md)

How do I change the location of the swagger documentation in the packaged app?

In build.sbt, add

swaggerTarget := new File("path/to/swagger/location")
How do I change the filename of the swagger documentation in the packaged app?

In build.sbt, add

swaggerFileName := "customSwagger.json"
How to output formatted json in swagger documentation file?

In build.sbt, add

swaggerPrettyJson := true
Support for generic types in schemas

Generic types in schema definitions for request/response body is supported. Example:

package models

case class Foo[T](payload: T)
case class AnotherOne(someString: String)

One can, then, reference the schema directly with models.Foo[models.AnotherOne] and a correct OpenAPI 3 spec will be generated (not tested with Swagger 2.0):

#   summary: Get a message
#   responses:
#       200:
#           description: success
#           content:
#               application/json:
#                   schema:
#                       $ref: '#/components/schemas/models.Foo[models.AnotherOne]'
GET     /message        controllers.AsyncController.parametric

The generated schema name, however, cannot contain [, ] or , which appear in type argument lists in Scala. Therefore, there's a default OutputTransformer (ParametricTypeNamesTransformerSpec) which normalises the name into the URL-compliant form. The definitions output would then look like:

  "components" : {
    "schemas" : {
      "models.AnotherOne" : {
        "properties" : {
          "someString" : {
            "type" : "string"
        "required" : [ "someString" ]
      "models.Foo-models.AnotherOne" : {
        "properties" : {
          "payload" : {
            "$ref" : "#/components/schemas/models.AnotherOne"
        "required" : [ "payload" ]
            "content" : {
              "application/json" : {
                "schema" : {
                  "$ref" : "#/components/schemas/models.Foo-models.AnotherOne"
Where to find more examples?

In the tests!

How to use markup in swagger specs

You can use markup on your swagger specs by providing OutputTransformers classes name to the setting swaggerOutputTransformers on your build file.

For example you can use environment variables by adding the configuration:

    swaggerOutputTransformers := Seq(envOutputTransformer)

Then on your routes file or root swagger file you can use some markup like the one used below for the host field:

  swagger: "2.0"
    title: "API"
    description: "REST API"
  host: ${API_HOST}

This way when the swagger file is parsed the markup ${API_HOST} is going to be substituted by the content of the environent variable API_HOST.

How to support OpenAPI/Swagger v3

You can produce swagger files for v3 by setting the flag:

  swaggerV3 := true

Make sure you also update your swagger markup to specify that you are using OpenAPI v3:

  openapi: 3.0.0
    title: "API"
    description: "REST API"
    version: "1.0.0"

Also, for $ref fields you will want to prefix paths with #/components/schemas/ instead of #/definitions/. For example:

#  parameters:
#    - name: body
#      schema:
#        $ref: '#/components/schemas/com.iheart.api.Track'
POST   /tracks       controller.Api.createTrack()
No #definitions generated when referencing other Swagger files

By placing a json or YAML file in conf/${dir}/${file} and referencing it with $ref in a comment, the file can be generated embedded in swagger.json.

⚠️ Warning: If a file that does not exist in /conf is specified, or if a typo is used for the filename, $ref:"${filename}" will be output as is.

example conf/routes file.

#  summary: Top Page
#  responses:
#    200:
#      $ref: './swagger/home_200.yml'
GET     /            controllers.HomeController.index

example conf/swagger/home_200.yml file.

description: "success"

Of course, writing schema etc. will also be embedded.

Generated swagger.json.

  "paths": {
    "/": {
      "get": {
        "operationId": "index",
        "tags": [
        "summary": "Top Page",
        "responses": {
          "200": {
            "description": "success"

See the following document for information on how to refer to other files by "$ref".


You can also cut out the entire comment.

This feature is very useful, but OpenAPI does not allow top-level $ref, so failing to embed it may result in an invalid swagger.json!

#  $ref: './swagger/home.yml'
GET     /            controllers.HomeController.index

example home.yml file.

summary: Top Page
      description: "success"
Duplicate operationId?

It can be configured in build.sbt. This setting allows you to set the ${controllerName}.${methodName} to name the operationId.

swaggerOperationIdNamingFully := true
Need a schema description?

Using runtime-scaladoc-reader, a description can be generated from Scaladoc comments written in the case class.

⚠️ Schema generation from documentation comments is very useful, but should never be used if the scope of scaladoc documentation is different from the scope of OpenAPI documentation.

Add the required dependencies and Compiler Plugin to build.sbt and configure it for use.

embedScaladoc := true
addCompilerPlugin("com.github.takezoe" %% "runtime-scaladoc-reader" % "1.0.3")
libraryDependencies +=  "com.github.takezoe" %% "runtime-scaladoc-reader" % "1.0.3"

For example, a case class might be written as follows.

  * @param name e.g. Sunday, Monday, TuesDay...
case class DayOfWeek(name: String)

The generated JSON will look like this.

  "DayOfWeek": {
    "properties": {
      "name": {
        "type": "string",
        "description": "e.g. Sunday, Monday, TuesDay..."
    "required": [
Is play java supported?

you can generate models definition from java POJO by setting the flag:

  playJava := true

The flag only suport PlayJava 2.7 and 2.8