---
title: Build a library
framework: swift-org
role: article
path: swift-org/getting-started/library-swiftpm
---

# Build a library

The source code for this guide can be found [on GitHub](https://github.com/apple/swift-getting-started-package-library)

## Installing Swift

To kickstart your journey, [install Swift](/docs/swift-org/install/) to begin using it on **macOS**, **Linux**, or **Windows**.

Tip: To test that you have Swift installed, run `swift --version` from your shell or terminal app.

Swift comes bundled with the [Swift Package Manager (SwiftPM)](/docs/swift-package-manager/documentation/packagemanagerdocs/) that manages the distribution of Swift code. It allows easy importing of other Swift packages into your applications and libraries, making it a valuable tool for any Swift developer.

Swift is covered by the [Apache License, Version 2.0](https://swift.org/LICENSE.txt).

## Bootstrapping

Let’s write a small library with our new Swift development environment. To start, we’ll use SwiftPM to make a new project for us. In your terminal of choice run:

``` $ mkdir MyLibrary $ cd MyLibrary $ swift package init --name MyLibrary --type library ```

This will generate a new directory called *MyLibrary* with the following files:

``` . ├── Package.swift ├── Sources │   └── MyLibrary │       └── MyLibrary.swift └── Tests     └── MyLibraryTests         └── MyLibraryTests.swift ```

`Package.swift` is the manifest file for Swift. It’s where you keep metadata for your project, as well as its dependencies.

`Sources/MyLibrary/MyLibrary.swift` is the library initial source file and where we’ll write our library code. `Test/MyLibraryTests/MyLibraryTests.swift` is where we can write tests for our library.

In fact, SwiftPM generated a “Hello, world!” project for us, including some unit tests! We can run the tests by running `swift test` in our terminal.

``` $ swift test Building for debugging... [5/5] Linking MyLibraryPackageTests Build complete! (7.91s) Test Suite 'All tests' started at 2025-08-01 14:02:39.232. Test Suite 'All tests' passed at 2025-08-01 14:02:39.233.    Executed 0 tests, with 0 failures (0 unexpected) in 0.000 (0.001) seconds ◇ Test run started. ↳ Testing Library Version: 6.1 (43b6f88e2f2712e) ↳ Target Platform: arm64-apple-macosx ◇ Test example() started. ✔ Test example() passed after 0.001 seconds. ✔ Test run with 1 test passed after 0.001 seconds. ```

## A small library

Now let’s write a small library. Replace the example content of `MyLibrary.swift` with the following code:

``` import Foundation

struct Email: CustomStringConvertible {   var description: String

public init(_ emailString: String) throws {     let regex = #"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,64}"#     guard let _ = emailString.range(of: regex, options: .regularExpression) else {       throw InvalidEmailError(email: emailString)     }     self.description = emailString   } }

private struct InvalidEmailError: Error {   let email: String } ```

Now let’s add a unit test for this strongly typed Email API. Replace the example content of `MyLibraryTests.swift` with the following code:

``` import Testing @testable import MyLibrary

struct MyLibraryTests {   @Test func email() throws {     let email = try Email("john.appleseed@apple.com")     #expect(email.description == "john.appleseed@apple.com")

#expect(throws: (any Error).self) {       try Email("invalid")     }   } } ```

Once we save that, we can run the tests again:

``` $ swift test Building for debugging... [5/5] Linking MyLibraryPackageTests Build complete! (3.09s) Test Suite 'All tests' started at 2025-08-01 14:24:32.687. Test Suite 'All tests' passed at 2025-08-01 14:24:32.689.    Executed 0 tests, with 0 failures (0 unexpected) in 0.000 (0.001) seconds ◇ Test run started. ↳ Testing Library Version: 6.1 (43b6f88e2f2712e) ↳ Target Platform: arm64-apple-macosx ◇ Suite MyLibraryTests started. ◇ Test email() started. ✔ Test email() passed after 0.001 seconds. ✔ Suite MyLibraryTests passed after 0.001 seconds. ✔ Test run with 1 test passed after 0.001 seconds. ```

The source code for this guide can be found [on GitHub](https://github.com/apple/swift-getting-started-package-library).