Pubspec Format

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 will be hosted on
Required for packages that will be hosted on
Can be omitted if your package has no dependencies.
Dev dependencies
Can be omitted if your package has no dev dependencies.
Dependency overrides
Can be omitted if you do not need to override any dependencies.
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 will be 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've been looking
author: Nathan Weizenbaum <>
  efts: '>=2.0.4 <3.0.0'
  transmogrify: '>=0.4.0 <1.0.0'
  unittest: '>=0.6.0'
    path: ../transmogrify_patch/


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

It should be all lowercase, with underscores to separate words, just_like_this. Stick with basic Latin letters and Arabic digits: [a-z0-9_] and ensure that it’s a valid Dart identifier (i.e. 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 will 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 will 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 (e.g. Nathan Weizenbaum) or a name and an email address (e.g. Nathan Weizenbaum <>). For example:

- Nathan Weizenbaum <>
- Bob Nystrom <>

If anyone uploads your package to, your email address will be public.


This should be a URL pointing to the website for your package. For hosted packages, this URL will be 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: GitHub,, whatever.


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 will be shown on your package’s page.


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.

SDK constraints

A package can indicate which versions of its dependencies it supports, but there is also another implicit dependency all packages have: the Dart SDK itself. Since the Dart 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 Dart SDK from 0.3.4 or later:

  sdk: ">=0.3.4"

Pub will try to find the latest version of a package whose SDK constraint works with the version of the Dart SDK that you have installed.