Swift Online Compiler | Free Online Compiler

Code

print("Hello, Swift!")

STDIN (optional)

Args (space separated)

Output

What Is the Swift Online Compiler?

This tool lets you compile and run Swift programs directly in your browser without installing Xcode or the Swift toolchain on your machine. Whether you are learning Swift for the first time or quickly testing optionals, closures, and protocol-oriented patterns, this compiler provides a fast way to write and execute Swift code online.

Swift does not require a main function for top-level code. You can write executable statements directly at the file level, or define functions, structs, and classes and call them from top-level code. Use print() to display output and readLine() to read input from standard input.

All code executes on a remote sandboxed server powered by the Piston API. Your browser sends the source code to the server, which compiles it with the Swift compiler and runs the resulting binary inside an isolated container. Swift's type safety, optional checking, and other compiler diagnostics are fully enforced during compilation.

How It Works

Write your Swift code in the editor panel. The editor starts with a simple "Hello, Swift!" example using print(), but you can replace it with any valid Swift program.
Provide input in the STDIN field if your program reads from standard input using readLine(). Leave this field empty if your program does not require input.
Add command-line arguments in the Args field if your program reads from CommandLine.arguments. Enter arguments separated by spaces.
Click the Run button to send your code to the Piston execution server. The server compiles your Swift source code and then executes the resulting binary, capturing all output.
View the results in the Output panel. You will see everything your program prints to standard output, along with any compiler errors including type mismatches, optional unwrapping failures, or runtime errors.

Step-by-Step Example

Suppose you want to write a program that reads a name from standard input and uses optionals with guard statements. Here is how you would do it using this compiler:

First, type the following code into the editor panel:

func greet(_ input: String?) {
    guard let name = input?.trimmingCharacters(in: .whitespacesAndNewlines),
          !name.isEmpty else {
        print("Hello, stranger!")
        return
    }
    print("Hello, \(name)!")
}

let input = readLine()
greet(input)

This example demonstrates several Swift features: optional parameters with String?, guard let for safe unwrapping, string interpolation with \(), and the readLine() function for reading standard input.

Next, go to the STDIN field and type a name, for example Alice. This value will be read by readLine() when the program runs.

Now click the Run button. The compiler first builds your Swift source code, then executes it with the provided input. After a moment, the Output panel displays the result:

Hello, Alice!

If you leave the STDIN field empty and click Run again, the output changes to show the guard fallback. This workflow makes it easy to test different inputs and observe how optionals and control flow behave.

Use Cases

Learning Swift fundamentals. Beginners can experiment with variables, constants, optionals, control flow, closures, and value types in a zero-setup environment.
Testing optionals and unwrapping. Quickly verify how optional binding, nil coalescing, guard statements, and forced unwrapping behave with different inputs.
Practicing protocols and extensions. Experiment with protocol-oriented programming, protocol extensions, default implementations, and associated types.
Exploring closures and higher-order functions. Test map, filter, reduce, compactMap, and custom closure syntax to understand functional patterns in Swift.
Preparing for coding interviews. Many interview questions can be solved in Swift. Use this compiler to practice problems, test edge cases, and refine solutions quickly.

Limitations and Notes

Single file execution only. This compiler runs a single Swift file (main.swift). Multi-file projects and separate modules are not supported.
No Swift Package Manager. SPM and external dependencies are not available. Only the Swift standard library and partial Foundation support are accessible.
No UI frameworks. SwiftUI, UIKit, and AppKit are not available. This compiler supports command-line programs only.
Foundation is partially available. Core Foundation types may work, but platform-specific APIs and frameworks beyond Foundation are not accessible.
No file I/O access. The sandboxed environment does not allow reading from or writing to the filesystem. File operations will fail at runtime.
Execution timeout applies. Programs that take too long or enter infinite loops are terminated automatically to prevent resource exhaustion.
Standard library is fully available. You can use all Swift standard library types including Array, Dictionary, Set, String, and their associated methods.

Frequently Asked Questions

What Swift version does this compiler use?

It uses the latest Swift version available through the Piston execution engine.

Does this compiler support optionals and unwrapping?

Yes, all optional features work including optional binding with if let, guard let, nil coalescing, and forced unwrapping.

Is the Foundation framework available?

Foundation is partially available. Core types like Date, URL, and JSONSerialization may work, but platform-specific APIs are not supported.

Can I build SwiftUI apps?

No, SwiftUI and other UI frameworks are not available. This compiler supports command-line Swift programs only.

Can I use readLine() for input?

Yes, use readLine() in your code and provide the input data in the STDIN field before running.

Does this support structs and classes?

Yes, you can define and use both structs and classes with properties, methods, initializers, protocols, and extensions.

Can I use Swift Package Manager?

No, Swift Package Manager is not available. Only the Swift standard library and partially available Foundation are accessible.

Does error handling with try/catch work?

Yes, Swift error handling works including do-try-catch blocks, throwing functions, and the try? and try! operators.

Swift Compiler