Packages and pub

A package is a reusable bundle of Dart code. pub is Dart's package manager, and pub.dev is the public repository, with tens of thousands of packages for HTTP, state management, databases, and much more.

pubspec.yaml

Every Dart project has a pubspec.yaml describing it and its dependencies:

name: expense_tracker
description: A small expense tracker.
version: 1.0.0

environment:
  sdk: ^3.5.0

dependencies:
  http: ^1.2.0

dev_dependencies:
  lints: ^5.0.0
  test: ^1.25.0

• dependencies are needed to run the program; dev_dependencies only during development (tests, lints).
• ^1.2.0 (a caret constraint) means "1.2.0 or newer, but below 2.0.0" — compatible updates without breaking changes.

Adding packages

dart pub add http
dart pub add --dev test

This updates pubspec.yaml and downloads the packages. pub records the exact versions it chose in pubspec.lock. Commit the lock file for apps, so everyone builds with the same versions. (In Flutter projects, use flutter pub add.)

Importing

import 'dart:math';                     // a core library
import 'package:http/http.dart' as http; // a package, with a prefix
import 'src/models.dart';               // a file in your own project

as http adds a prefix, so its names are written http.get(...) — avoiding clashes with your own names.

Choosing packages

On pub.dev, check each package's likes, pub points (a quality score), popularity, publisher, and recent updates. Packages marked Flutter Favorite have been reviewed for quality. Every dependency is code you trust to run in your app — prefer fewer, well-maintained ones.

Common mistakes

• Editing pubspec.yaml and forgetting to run dart pub get (most editors do this automatically on save).
• Adding packages for things the core libraries already do.