Quick overview: Swift
Use the editor above to run a small Swift idea without setting up a project first. Runs Swift through Piston from main.swift, using the Swift toolchain available in the runner image. Run it. Read the output. Then change one thing, because the fastest debugging session is usually the one with the fewest moving parts.
We built this page for short checks: optionals, structs, enums, closures, arrays, dictionaries, and console-style input. It is deliberately narrower than a local environment, and that is the point; when a snippet is only twenty lines long, a full toolchain can get in the way of the question you actually have.
Online Swift usually behaves like command-line Swift on Linux, so Apple-platform frameworks such as UIKit are not part of the deal. This page is great for optionals and collections. It is the wrong place for iOS UI work.
What happens when Run fires
- Start with the smallest Swift snippet that can show the behavior.
- Add input only when the program reads it. Empty STDIN is a valid test case.
- Press Run, inspect stdout and stderr, then change one line. That rhythm keeps accidental fixes from hiding the real bug.
The mechanics are simple. We keep the run cycle compact because this page is meant to answer one question at a time, not manage a full project tree.
That style also makes the result easier to share. A reader can scan a short Swift snippet, run it, and see the same error without first recreating your directory structure or guessing which dependency you forgot to mention.
Try it small
The saved example below is intentionally left unchanged. Run it once as written, then make a small edit and run it again; that gives you a known-good baseline before you test your own idea.
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)The next preserved block belongs to the same example. Keep it nearby when you are comparing input, output, or the shape of the result. Small examples expose mistakes quickly.
Hello, Alice!After the sample works, try one edge case that exercises the page's limits. Online Swift usually behaves like command-line Swift on Linux, so Apple-platform frameworks such as UIKit are not part of the deal. That single change often teaches more than pasting a large program and trying to guess which part failed.
Caveats before use
This page is strongest when the problem is small and visible. It is weakest when the problem depends on SwiftUI, UIKit, package resolution, Apple SDK APIs, and device-specific behavior. Two caveats.
- Do not paste secrets, tokens, private URLs, or customer data.
- The environment is intentionally constrained, so a snippet that works here still deserves a local check when compiler flags, packages, server state, or exact versions matter.
- Timeouts are normal for runaway loops. They protect the shared runner.
We deliberately keep the sandbox narrow. That makes the output easier to trust for optionals, structs, enums, closures, arrays, dictionaries, and console-style input, while making it clear when you have outgrown the page.
One practical test: if you cannot explain the snippet in one sentence, split it. The runner is happiest when each run answers a single question, and you will be happier too when the error message points at one idea instead of a pile of guesses.
Questions people actually ask
Only a few questions belong here. The goal is to answer the mistakes that actually interrupt a small Swift run, not to pad the page.
Does Swift compile to machine code?
Swift is compiled to native code for its target platform. In local Apple development, Xcode and the Swift compiler handle that build. Online Swift runners are usually command-line environments, so they are good for optionals, structs, enums, and algorithms, not for testing UIKit or SwiftUI apps. For example, swift main.swift runs a small script-style Swift file. Online Swift usually behaves like command-line Swift on Linux, not like an iOS app with Apple UI frameworks.
Is Swift compiled or interpreted?
Swift is a compiled language. It can feel script-like when you run a single file with the swift command, but the toolchain is still compiling code behind the scenes. For app development, Xcode builds the project. For this page, keep examples console-friendly and small. Online Swift usually behaves like command-line Swift on Linux, not like an iOS app with Apple UI frameworks.
Can Xcode 10.2 still compile Swift 4.2?
Xcode 10.2 is old, and Swift compatibility depends on the language mode and project settings. It may work with Swift 4.2 code in some projects, but you should check the project’s Swift Language Version setting. For current work, use a newer Xcode unless you are maintaining an old app. For example, swift main.swift runs a small script-style Swift file.
How to run Swift code online?
Paste your Swift code in the editor - functions, structs, classes, the works. If you read stdin via readLine, put input in the STDIN field. Click Run, and the result appears in the Output panel. No Xcode or macOS required.
Is this Swift playground free to use?
Yes, free and browser-based with no signup. It runs on any operating system, including Windows and Linux, so you can practice Swift even without a Mac.
Can I use this for Swift programming practice?
Yes - closures, optionals, protocols, generics, and small algorithm exercises all work. For UIKit, SwiftUI, or anything platform-specific, you'll need Xcode and macOS.
Where it fits
Use it when you are stuck on someone else's machine, teaching a small concept, or separating a language question from a project question. No ceremony.
It also works well as a note-taking tool: paste the final snippet into your lesson, issue, or commit message after you have proved it in the runner.
Keep the example slightly smaller than feels natural. That sounds fussy, but it prevents a common debugging mistake: changing five pieces of code, getting a different result, and no longer knowing which piece mattered.
Further reading
Reference pages are better than folklore when an error message gets specific. Start with official docs, then use tutorials for context once the rule is clear.
Related compilers
One last practical note: keep a tiny passing snippet next to the failing one. The comparison often makes the missing assumption obvious, and it keeps the page useful without turning a quick runner into a pretend project workspace.