Swift library which can generate output compatible with OpenAPI 3.1.0


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SwiftOpenAPI is a Swift library which can generate output compatible with OpenAPI version 3.1.0. You can describe your API using OpenAPIObject type.
The main accent in the library is on simplifying the syntax: the active use of literals (array, dictionary, string etc) and static methods greatly simplifies writing and reading OpenAPI docs in Swift.

Short example

try OpenAPIObject(
    openapi: "3.0.11",
    info: InfoObject(
        title: "Example API",
        version: "0.1.0"
    servers: [
    paths: [
        "services": .get(
            summary: "Get services",
            OperationObject(description: "Get services")
        "login": .post(
                description: "login",
                requestBody: .ref(components: \.requestBodies, "LoginRequest"),
                responses: [
                    .ok: .ref(components: \.responses, "LoginResponse"),
                    .unauthorized: .ref(components: \.responses, "ErrorResponse")
        "/services/{serviceID}": [
            .get: OperationObject(description: "Get service"),
            .delete: OperationObject(description: "Delete service")
        "/services": .ref(components: \.pathItems, "T")
    components: ComponentsObject(
        schemas: [
            "LoginBody": [
                "username": .string,
                "password": .string
            "LoginResponse": .value(.encode(LoginResponse.example))
        examples: [
            "LoginBody": [
                "username": "SomeUser",
                "password": "12345678"
            "LoginResponse": .value(
            	ExampleObject(value: .encode(LoginResponse.example))
        requestBodies: [
            "LoginRequest": .value(
                    content: [
                        .application(.json): MediaTypeObject(
                            schema: .ref(components: \.schemas, "LoginBody")
                    required: nil

Pets store example

PetsSwagger.swift demonstrates syntaxis well

Creating schemas and parameters for Codable types

There is a possibility to create SchemeObject, [ParameterObject], AnyValue and [String: HeaderObject] instances from Codable types. It's possible to use SchemeObject.decode/encode, [ParameterObject].decode/encode, [String: HeaderObject].decode/encode and AnyValue.encode methods for it.

let loginBodySchemeFromType: SchemeObject = try .decode(LoginBody.self)
let loginBodySchemeFromInstance: SchemeObject = try .encode(LoginBody.example)
let loginBodyExample = try ExampleObject(value: .encode(LoginBody.example))

You can customize the encoding/decoding result by implementing OpenAPIDescriptable and OpenAPIType protocols.

  1. OpenAPIDescriptable protocol allows you to provide a custom description for the type and its properties. @OpenAPIAutoDescriptable macro implements this protocol with your comments.
import SwiftOpenAPI

/// Login request body.
struct LoginBody: Codable {
    /// Username string.
    let username: String
    /// Password string. Encoded.
    let password: String


struct LoginBody: Codable, OpenAPIDescriptable {
    let username: String
    let password: String
    static var openAPIDescription: OpenAPIDescriptionType? {
        OpenAPIDescription<CodingKeys>("Login request body.")
            .add(for: .username, "Username string.")
            .add(for: .password, "Password string. Encoded.")
  1. OpenAPIType protocol allows you to provide a custom schema for the type.
struct Color: Codable, OpenAPIType {
    static var openAPISchema: SchemaObject {
        .string(format: "hex", description: "Color in hex format")

Specification extensions

While the OpenAPI Specification tries to accommodate most use cases, additional data can be added to extend the specification at certain points.\

var api = OpenAPIObject(...)
api.specificationExtensions = ["x-some-extension": "some value"]
// or
api.specificationExtensions = try? SpecificationExtensions(from: someEncodable)

It was a bit tricky challenge to implement additional dynamic properties for any codable struct. The solution is to use SpecificationExtendable protocol in combination with WithSpecExtensions property wrapper. There is two ways to decode/encode SpecificationExtendable types with additional properties:

  1. Use SpecificationExtendable.json, SpecificationExtendable.Type.from(json:) methods.
let schema = try SchemaObject.from(json: jsonData)
let jsonData = try schema.json()
  1. If you cannot use custom decoding methods, you can use WithSpecExtensions wrapper.
let api = try WithSpecExtensions(wrappedValue: OpenAPIObject(...))
let jsonData = try JSONEncoder().encode(api)


  • URI type instead of String
  • refactor method on OpenAPIObject (?)
  • Extend RuntimeExpression type
  • DataEncodingFormat


  1. Swift Package Manager

Create a Package.swift file.

// swift-tools-version:5.9
import PackageDescription

let package = Package(
  name: "SomeProject",
  dependencies: [
    .package(url: "https://github.com/dankinsoid/SwiftOpenAPI.git", from: "2.20.0")
  targets: [
    .target(name: "SomeProject", dependencies: ["SwiftOpenAPI"])
$ swift build

Related projects


dankinsoid, voidilov@gmail.com


SwiftOpenAPI is available under the MIT license. See the LICENSE file for more info.


  • Swift Tools 5.9.0
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Last updated: Tue Apr 02 2024 12:39:55 GMT-0900 (Hawaii-Aleutian Daylight Time)