This section explains many of the concepts surrounding the Unity Package Manager functionality:
Multiple versions of each package are available, marking changes to that package along its life cycle. Every time a developer updates the package, they give it a new version number. A change in package version tells you whether it contains a breaking change (major), a new backward-compatible functionality (minor), or bug fixes only (patch), following Semantic Versioning.
To view the list of versions available for a specific package, see Finding a specific version.
There are two types of manifest files:
manifest.json) These store information that the Package Manager needs to locate and load the right packages, including a list of packages and versions declared as dependencies.
package.json). These store information about a specific package, and a list of packages and versions that the package requires.
Unity maintains a central registry of official packages that are available for distribution. A package registry stores package contents and information (metadata) on each package version. By default, all projects use the official Unity package registry, but you can add additional registries to store and distribute private packages or stage packages in development.
The Unity Package Manager is a tool that manages the entire package system. Its primary tasks include the following:
The Unity Package Manager installs samples, tools, and assets on a per-project basis, rather than installing them across all projects for a specific machine or device. It uses a global cache to store downloaded package metadata and contents. Once installed, Unity treats package assets just like any other asset in the project, except that these assets are stored inside the package folder and are immutable. You can only permanently change content from Local and Embedded package sources.
After developing a package to the point where it is ready for Unity users to test it and provide feedback, a package enters the Preview state. Packages in this state usually appear in the Unity Editor with the preview label and often use
preview as part of their version.
Unity’s release management only grants a package the verified status after it passes several testing stages and validation procedures, which also include checks for appropriate documentation, changelog, and license files. Packages in this state may appear in the Unity Editor with the 2019.3 verified label and never use
preview as part of their version.
If the package developer introduces changing or breaking changes to a package (either by introducing a change that breaks an API or affects its usage), that package returns to the Preview state and the Package Manager does not suggest the new preview package as a possible update for the verified version.
These states indicate where the package is in the development cycle:
|In Development||The package developer creates the package. Usually this corresponds to having the package embedded in the developer’s project.|
|Preview||When the package is ready for testing, the Unity package developer makes sure there is some basic test coverage, and that the package passes testing with the package validation suite. The package also needs at least preliminary documentation, an updated changelog, and licensing before the Unity package developer can apply to publish the package on Unity’s official registry.
At this point, the package is available for testing, so that any eligible Unity user can provide the developer with feedback. Most packages are available to any Unity users, although a few packages are limited to Unity IDs with specific entitlements.
Preview packages can go through many changes before they are ready to be verified for a specific version of Unity. At some point in the future, they might pass the verification requirements; however, they might also be deprecated instead. Because there is no guarantee for future support, you should not use preview packages in production. For a list of preview packages available for this version, see Preview packages.
|Verified||The package has undergone rigorous testing and has been verified to work safely with this specific version of Unity, and all other packages verified for the same version. This state is only for packages that Unity develops internally. Contact third-party package developers to ask about their specific processes.
When a package is verified for a version of Unity, Unity guarantees to support that verified package for the duration of that version of Unity, throughout the period of long-term support, and does not allow any major or minor updates (that is, changes that break or change an API). With each new version of Unity, each verified package must go through the verification process again before the Package Manager considers it verified.
To see a list of packages that are verified for this version of Unity, see Verified packages.
Note: Some packages are neither verified nor preview packages. In many cases, this is because a package was verified in a previous version of Unity but has not completed the verification process yet for the current version. For a few packages, they were published to the Unity Package Manager registry because they were considered safe to use, but were never verified. In both of these cases, these packages are safe to use in production.
The Package Manager window displays a tag that corresponds to some of these states.
Sources describe where the package came from:
|Registry||The Unity Package Manager downloads most packages from a package registry into a global cache on your computer as you request them. These packages are immutable, so you can use them in your project, but you cannot modify them or change their package manifests.|
|Built-in||These packages allow you to enable or disable Unity features (for example, Terrain Physics, Animation, etc.). They are immutable. For more information, see Built-in packages.|
|Embedded||Any package stored inside your project folder is embedded. This source corresponds with the in development state because you typically put all the scripts, libraries, samples, and other assets your new package needs in a folder under your project folder when you begin development on a package.|
|Local||You can install a package from any folder on your computer (for example, if you have cloned a development repository locally).|
|Local tarball||You can install a package from a tarball file on your computer. The Package Manager extracts the package from the tarball and stores it in the cache. However, these packages are immutable, unlike installations from a Local folder.|
|Git||The Package Manager installs Git packages directly from a Git repository instead of from the registry server.|
To edit the package manifest for a package, see Inspecting packages.
The Package Manager window displays a tag that corresponds to some of these sources. For more information, see Tags.