Your First Dart Program

Every Dart application, whether a CLI script, a server, or a Flutter app under the hood, needs exactly one top-level main() function as its entry point; this is where execution begins when you run the program. The simplest possible Dart program is three lines: void main() { print('Hello, World!'); }. The void return type means main() doesn't hand back a value to the operating system, print() is a top-level function from dart:core (automatically imported into every Dart file, no import statement needed) that writes a line to standard output, and the whole file can be saved as any .dart filename, though CLI projects conventionally name the entry file after the package inside a bin/ folder.

Beyond the bare minimum, a realistic Dart file typically starts with import statements (for dart:core extras like dart:math, or third-party packages from pub.dev), followed by top-level declarations — functions, classes, or constants — and finally the main() function that ties them together by calling into that code. Dart executes statements inside main() sequentially, top to bottom, just like most imperative languages, but functions and classes defined elsewhere in the file can be referenced from main() regardless of whether they're declared above or below it, because Dart resolves top-level declarations before execution starts. Command-line arguments passed when running the program arrive as List<String> arguments if you declare main() as void main(List<String> arguments).

With the Dart SDK installed, save your code as hello.dart and run it from the terminal with dart run hello.dart, which JIT-compiles and executes the file in one step, ideal for quick iteration. For a proper CLI project created with dart create my_app, the entry file lives at bin/my_app.dart, and you run it with dart run from the project root, which automatically finds that entry point. When you're ready to ship a standalone executable, dart compile exe bin/my_app.dart AOT-compiles it into a native binary that runs without needing the Dart SDK installed on the target machine at all, useful for distributing a CLI tool to users who don't have Dart set up.

DartPad, hosted at dartpad.dev, is an in-browser Dart editor and compiler that requires no installation at all — you type Dart (or even a minimal Flutter widget) directly into the page and click Run to see console output or a rendered UI immediately, powered by a server-side compiler rather than anything installed on your machine. It's the fastest way to experiment with a language feature, test a small snippet from documentation, or follow along with a tutorial without touching a terminal, though it isn't a replacement for a real project once you're building something with multiple files, external packages, or platform-specific code that needs a local SDK and editor.