Package layout conventions

Contents

The pubspec
LICENSE
README.md
CHANGELOG.md
Public directories
- Public libraries
- Public tools
Public assets
Implementation files
Web files
Command-line apps
Tests and benchmarks
Documentation
Examples
Internal tools and scripts
Project-specific caching for tools

When you build a pub package, we encourage you to follow the conventions that this page describes. They describe how you organize the files and directories within your package, and how to name things.

Here’s what a complete package (named enchilada) that uses every corner of these guidelines might look like:

enchilada/
  .dart_tool/ *
  pubspec.yaml
  pubspec.lock **
  LICENSE
  README.md
  CHANGELOG.md
  benchmark/
    make_lunch.dart
  bin/
    enchilada
  doc/
    api/ ***
    getting_started.md
  example/
    main.dart
  lib/
    enchilada.dart
    tortilla.dart
    guacamole.css
    src/
      beans.dart
      queso.dart
  test/
    enchilada_test.dart
    tortilla_test.dart
  tool/
    generate_docs.dart
  web/
    index.html
    main.dart
    style.css

* The .dart_tool/ directory exists after you’ve run dart pub get. Don’t check it into source control. To learn more, see Project specific caching for tools.

** The pubspec.lock file exists after you’ve run dart pub get. Leave it out of source control unless your package is an application package.

*** The doc/api directory exists locally after you’ve run dart doc. Don’t check the api directory into source control.

The pubspec

enchilada/
  pubspec.yaml
  pubspec.lock

Every package has a pubspec, a file named pubspec.yaml, in the root directory of the package. That’s what makes it a package.

Running dart pub get, dart pub upgrade, or dart pub downgrade on the package creates a lockfile, named pubspec.lock. If your package is an application package, check the lockfile into source control. Otherwise, don’t.

For more information, see the pubspec page.

LICENSE

enchilada/
  LICENSE

If you’re publishing your package, include a license file named LICENSE. We recommend using an OSI-approved license such as BSD-3-Clause, so that others can reuse your work.

README.md

enchilada/
  README.md

One file that’s very common in open source is a README file that describes the project. This is especially important in pub. When you upload to the pub.dev site, your README.md file is shown—rendered as Markdown—on the page for your package. This is the perfect place to introduce people to your code.

For guidance on how to write a great README, see Writing package pages.

CHANGELOG.md

enchilada/
  CHANGELOG.md

Include a CHANGELOG.md file that has a section for each release of your package, with notes to help users of your package upgrade. Users of your package often review the changelog to discover bug fixes and new features, or to determine how much effort it will take to upgrade to the latest version of your package.

To support tools that parse CHANGELOG.md, use the following format:

Each version has its own section with a heading.
The version headings are either all level 1 or all level 2.
The version heading text contains a package version number, optionally prefixed with “v”.

When you upload your package to the pub.dev site, your package’s CHANGELOG.md file (if any) appears in the Changelog tab, rendered as Markdown.

Here’s an example of a CHANGELOG.md file. As the example shows, you can add subsections.

# 1.0.1

* Fixed missing exclamation mark in `sayHi()` method.

# 1.0.0

* **Breaking change:** Removed deprecated `sayHello()` method.
* Initial stable release.

## Upgrading from 0.1.x

Change all calls to `sayHello()` to instead be to `sayHi()`.

# 0.1.1

* Deprecated the `sayHello()` method; use `sayHi()` instead.

# 0.1.0

* Initial development release.

Public directories

Two directories in your package are public to other packages: lib and bin. You place public libraries in lib and public tools in bin.

Public libraries

The following directory structure shows the lib portion of enchilada:

enchilada/
  lib/
    enchilada.dart
    tortilla.dart

Many packages are library packages: they define Dart libraries that other packages can import and use. These public Dart library files go inside a directory called lib.

Most packages define a single library that users can import. In that case, its name should usually be the same as the name of the package, like enchilada.dart in the example here. But you can also define other libraries with whatever names make sense for your package.

When you do, users can import these libraries using the name of the package and the library file, like so:

import 'package:enchilada/enchilada.dart';
import 'package:enchilada/tortilla.dart';

If you want to organize your public libraries, you can also create subdirectories inside lib. If you do that, users will specify that path when they import it. Say you have the following file hierarchy:

enchilada/
  lib/
    some/
      path/
        olives.dart

Users import olives.dart as follows:

import 'package:enchilada/some/path/olives.dart';

Note that only libraries should be in lib. Entrypoints—Dart scripts with a main() function—cannot go in lib. If you place a Dart script inside lib, you will discover that any package: imports it contains don’t resolve. Instead, your entrypoints should go in the appropriate entrypoint directory.

For more information on library packages, see Creating packages.

Public tools

Dart scripts placed inside of the bin directory are public. If you’re inside the directory of a package, you can use dart run to run scripts from the bin directories of any other package the package depends on. From any directory, you can run scripts from packages that you have activated using dart pub global activate.

If you intend for your package to be depended on, and you want your scripts to be private to your package, place them in the top-level tool directory. If you don’t intend for your package to be depended on, you can leave your scripts in bin.

Public assets

enchilada/
  lib/
    guacamole.css

While most library packages exist to let you reuse Dart code, you can also reuse other kinds of content. For example, a package for Bootstrap might include a number of CSS files for consumers of the package to use.

These go in the top-level lib directory. You can put any kind of file in there and organize it with subdirectories however you like.

Implementation files

enchilada/
  lib/
    src/
      beans.dart
      queso.dart

The libraries inside lib are publicly visible: other packages are free to import them. But much of a package’s code is internal implementation libraries that should only be imported and used by the package itself. Those go inside a subdirectory of lib called src. You can create subdirectories in there if it helps you organize things.

You are free to import libraries that live in lib/src from within other Dart code in the same package (like other libraries in lib, scripts in bin, and tests) but you should never import from another package’s lib/src directory. Those files are not part of the package’s public API, and they might change in ways that could break your code.

How you import libraries from within your own package depends on the locations of the libraries:

When reaching inside or outside lib/ (lint: avoid_relative_lib_imports), use package:.
Otherwise, prefer relative imports.

For example:

// When importing from lib/beans.dart
import 'src/beans.dart';

// When importing from test/beans_test.dart
import 'package:enchilada/src/beans.dart';

The name you use here (in this case enchilada) is the name you specify for your package in its pubspec.

Web files

enchilada/
  web/
    index.html
    main.dart
    style.css

For web packages, place entrypoint code—Dart scripts that include main() and supporting files, such as CSS or HTML—under web. You can organize the web directory into subdirectories if you like.

Put library code under lib. If the library isn’t imported directly by code under web, or by another package, put it under lib/src. Put web-based examples under example. See Public assets for tips on where to put assets, such as images.

Command-line apps

enchilada/
  bin/
    enchilada

Some packages define programs that can be run directly from the command line. These can be shell scripts or any other scripting language, including Dart.

If your package defines code like this, put it in a directory named bin. You can run that script from anywhere on the command line, if you set it up using dart pub global.

Tests and benchmarks

enchilada/
  test/
    enchilada_test.dart
    tortilla_test.dart

Every package should have tests. With pub, the convention is that these go in a test directory (or some directory inside it if you like) and have _test at the end of their file names.

Typically, these use the test package.

enchilada/
  benchmark/
    make_lunch.dart

Packages that have performance critical code may also include benchmarks. These test the API not for correctness but for speed (or memory use, or maybe other empirical metrics).

Documentation

enchilada/
  doc/
    api/
    getting_started.md

If you have code and tests, the next piece you might want is good documentation. That goes inside a directory named doc.

When you run the dart doc tool, it places the API documentation, by default, under doc/api. Since the API documentation is generated from the source code, you should not place it under source control.

Other than the generated api, we don’t have any guidelines about format or organization of the documentation that you author. Use whatever markup format that you prefer.

Examples

enchilada/
  example/
    main.dart

Code, tests, docs, what else could your users want? Standalone example programs that use your package, of course! Those go inside the example directory. If the examples are complex and use multiple files, consider making a directory for each example. Otherwise, you can place each one right inside example.

In your examples, use package: to import files from your own package. That ensures that the example code in your package looks exactly like code outside of your package would look.

If you might publish your package, consider creating an example file with one of the following names:

example/example[.md]
example[/lib]/main.dart
example[/lib]/package_name.dart
example[/lib]/package_name_example.dart
example[/lib]/example.dart
example/README[.md]

When you publish a package that contains one or more of the above files, the pub.dev site creates an Example tab to display the first file it finds (searching in the order shown in the list above). For example, if your package has many files under its example directory, including a file named README.md, then your package’s Example tab displays the contents of example/README.md (parsed as Markdown.)

Internal tools and scripts

enchilada/
  tool/
    generate_docs.dart

Mature packages often have little helper scripts and programs that people run while developing the package itself. Think things like test runners, documentation generators, or other bits of automation.

Unlike the scripts in bin, these are not for external users of the package. If you have any of these, place them in a directory called tool.

Project-specific caching for tools

The .dart_tool/ directory is created when you run dart pub get and might be deleted at any time. Various tools use this directory for caching files specific to your project and/or local machine. The .dart_tool/ directory should never be checked into source control, or copied between machines.

It is also generally safe to delete the .dart_tool/ directory, though some tools might need recompute the cached information.

Example: The dart pub get tool will download and extract dependencies to a global $PUB_CACHE directory, and then write a .dart_tool/package_config.json file mapping package names to directories in the global $PUB_CACHE directory. The .dart_tool/package_config.json file is used by other tools, such as the analyzer and compilers when they need to resolve statements such as import 'package:foo/foo.dart'.

When developing a tool that needs project-specific caching, you might consider using the .dart_tool/ directory because most users already ignore it with .gitignore. When caching files for your tool in a user’s .dart_tool/ directory, you should use a unique subdirectory. To avoid collisions, subdirectories of the form .dart_tool/<tool_package_name>/ are reserved for the package named <tool_package_name>. If your tool isn’t distributed through the pub.dev site, you might consider publishing a placeholder package in order to reserve the unique name.

Example: package:build provides a framework for writing code generation steps. When running these build steps, files are cached in .dart_tool/build/. This helps speed-up future re-runs of the build steps.