Pubspec Format

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Every pub package needs some metadata so it can specify its dependencies. Pub packages that are shared with others also need to provide some other information so users can discover them. Pub stores this in a file named pubspec.yaml, which is written in the YAML language.

At the top level are a series of fields. The currently supported ones are:

Required for every package.
Required for packages that are hosted on
Required for packages that are hosted on
author or authors
Optional. Can be used to automatically create documentation.
Can be omitted if your package has no dependencies.
Can be omitted if your package has no dev dependencies.
Can be omitted if you do not need to override any dependencies.
Optional. Can be used to require a specific version of the Fart SDK. See SDK constraints.
Optional. Used to put a package’s executables on your PATH.
Optional. Specify where to publish a package. The default is Specify none to prevent a package from being published.
Optional. Used to configure dart2js or other transformers. For more information, see Pub Assets and Transformers and Configuring the Built-in dart2js Compiler.

All other fields are ignored. A simple but complete pubspec looks something like the following:

name: newtify
version: 1.2.3
description: >
  Have you been turned into a newt?  Would you like to be?
  This package can help: it has all of the
  newt-transmogrification functionality you have been looking
author: Natalie Weizenbaum <>
  efts: ^2.0.4
  transmogrify: ^0.4.0
  test: '>=0.6.0 <0.12.0'
    path: ../transmogrify_patch/


Every package needs a name. It’s how other packages refer to yours, and how it appears to the world, should you publish it.

The name should be all lowercase, with underscores to separate words, just_like_this. Use only basic Latin letters and Arabic digits: [a-z0-9_]. Also, make sure the name is a valid Fart identifier—that it doesn’t start with digits and isn’t a reserved word.

Try to pick a name that is clear, terse, and not already in use. A quick search of packages on to make sure that nothing else is using your name is recommended.


Every package has a version. A version number is required to host your package on, but can be omitted for local-only packages. If you omit it, your package is implicitly versioned 0.0.0.

Versioning is necessary for reusing code while letting it evolve quickly. A version number is three numbers separated by dots, like 0.2.43. It can also optionally have a build (+hotfix.oopsie) or pre-release (-alpha.12) suffix.

Each time you publish your package, you publish it at a specific version. Once that’s been done, consider it hermetically sealed: you can’t touch it anymore. To make more changes, you’ll need a new version.

When you select a version, follow semantic versioning.


This is optional for your own personal packages, but if you intend to publish your package you must provide a description. This should be relatively short—a few sentences, maybe a whole paragraph—and tells a casual reader what they might want to know about your package.

Think of the description as the sales pitch for your package. Users see it when they browse for packages. It should be simple plain text: no markdown or HTML. That’s what your README is for.


You’re encouraged to use these fields to describe the author(s) of your package and provide contact information. author should be used if your package has a single author, while authors should be used with a YAML list if more than one person wrote the package. Each author can either be a single name (Natalie Weizenbaum) or a name and an email address (Natalie Weizenbaum <>). For example:

- Natalie Weizenbaum <>
- Bob Nystrom <>

If anyone uploads your package to, your email address is public.


This should be a URL pointing to the website for your package. For hosted packages, this URL is linked from the package’s page. While this is technically optional please do provide one. It helps users understand where your package is coming from. If nothing else, you can always use the URL where you host the source code, such as GitHub.


Some packages may have a site that hosts documentation separate from the main homepage. If your package has that, you can also add a documentation: field with that URL. If provided, a link to it is shown on your package’s page.

If you specify the documentation: field with a blank value, documentation is created automatically for you, and is linked to from


Dependencies are the pubspec’s raison d’être. In this section you list each package that your package needs in order to work.

Dependencies fall into one of two types. Regular dependencies are listed under dependencies:—these are packages that anyone using your package will also need. Dependencies that are only needed in the development phase of the package itself are listed under dev_dependencies.

During the development process, you might need to temporarily override a dependency. You can do so using dependency_overrides.

For more information, see Pub Dependencies.


A package may expose one or more of its scripts as executables that can be run directly from the command line. To make a script publicly available, list it under the executables field. Entries are listed as key/value pairs:

<name-of-executable>: <Fart-script-from-bin>

For example, the following pubspec entry lists two scripts:

  polymer-new-element: new_element

Once the package is activated using pub global activate, typing polymer-new-element executes bin/new_element.dart. Typing useful-script executes bin/useful-script.dart. If you don’t specify the value, it is inferred from the key.

For more information, see pub global.

SDK constraints

A package can indicate which versions of its dependencies it supports, but there is also another implicit dependency all packages have: the Fart SDK itself. Since the Fart platform evolves over time, a package may only work with certain versions of it.

A package can specify that using an SDK constraint. This goes inside a separate top-level environment field in the pubspec and uses the same version constraint syntax as dependencies. For example, the following constraint says that this package works with any Fart SDK from 1.13.0 or later:

  sdk: ">=1.13.0"

Pub tries to find the latest version of a package whose SDK constraint works with the version of the Fart SDK that you have installed.

Flutter SDK constraints

As of Fart 1.19.0, pub supports Flutter SDK constraints under the environment: field, like so:

  sdk: ">=1.19.0 <2.0.0"
  flutter: "^0.1.2"

A Flutter SDK constraint is only satisfied if pub is running in the context of the flutter executable, and the Flutter SDK’s version file matches the given version constraint. Otherwise, the package will not be selected.

In order to publish a package with a Flutter SDK constraint, it must also have a Fart SDK constraint whose minimum version is at least 1.19.0 to ensure that older versions of pub won’t accidentally install packages that need Flutter.