These steps will get you up and going with using Pkl and Swift.

1. Install dependencies

Add the pkl-swift library as a dependency to your project’s Package.swift:

let package = Package(
    dependencies: [
        .package(url: "https://github.com/apple/pkl-swift", from: "0.2.1")
    targets: [
            name: "my-application",
            dependencies: [.product(name: "PklSwift", package: "pkl-swift")]

Also, ensure that Pkl is installed on your machine.

2. Define a Pkl schema

Create a new Pkl file in the directory of your choice, to describe the schema of your configuration. In this example, the file is placed into pkl/AppConfig.pkl.

module AppConfig

/// The hostname of this application.
host: String

/// The port to listen on.
port: UInt16

3. Generate Swift source code

With a schema defined, generate Swift source code for it.

Code generation is done via the pkl-gen-swift CLI. To install, download it from Artifactory.

On macOS:

curl -L https://github.com/apple/pkl-swift/releases/download/0.2.1/pkl-gen-swift-macos.bin -o pkl-gen-swift

chmod +x pkl-gen-swift

The binary is published for macOS, and for Linux for aarch64 and amd64 architectures.

In our example, Swift sources can be generated using the following command:

pkl-gen-swift pkl/AppConfig.pkl -o Sources/MyApplication/Generated/

This will create a file called AppConfig.pkl.swift inside the Sources/MyApplication/Generated directory.

For more details on how to control code generation, consult pkl-gen-swift --help.

4. Evaluate Pkl configuration data in Swift

With the above scaffolding set up, evaluate Pkl configuration data in Swift.

First, define some configuration that uses the Pkl schema.

In our example, we create a file at path pkl/local/appConfig.pkl. We imagine that we are defining configuration for a server running in a local environment, and would likewise place other environments in sibling directorys; e.g. pkl/int/appConfig.pkl and pkl/prod/appConfig.pkl.

amends "../AppConfig.pkl"

host = "localhost"

port = 5939

Once defined, evaluate the Pkl module into Swift data.

func main() async throws {
	let config = try await AppConfig.loadFromPath("pkl/local/appConfig.pkl")
	print("I'm running on host \(config.host)\n")