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:
<project>/Packagesdirectory. The Package Manager uses it to configure many things, including a list of dependencies for that Project, as well as any package repository to query for packages. More info
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 read-only 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 immutableYou cannot change the contents of an immutable (read-only) package. This is the opposite of mutable. Most packages are immutable, including packages downloaded from the package registry or by Git URL.
See in Glossary (read-only). You can only change Assets from Local and Embedded package sources.
States indicate where the package is in the development cycle:
|In Development||The package developer is still creating the package. Usually this corresponds to having the package embedded in the developer’s Project.|
|Preview||Preview packages are packages that are not production-ready and you should only use them for testing. For more information, see Preview packagesA preview package is in development and not yet ready for production. A package in preview might be at any stage of development, from the initial stages to near completion.
See in Glossary.
|Production-ready||The package is safe to use in production and the developer has published it to the package registry.|
|Verified||The package has undergone testing and has been verified to work safely with this specific version of Unity, and all other packages verified for the same version. To see a list of packages that are verified for this version of Unity, see Verified packagesWhen a package passes release cycle testing for a specific version of Unity, it receives the Verified For designation. This means that these packages are guaranteed to work with the designated version of Unity.
See in Glossary.
The Package Manager window displays a tag that corresponds to some of these states. For more information, see TagsA reference word which you can assign to one or more GameObjects to help you identify GameObjects for scripting purposes. For example, you might define and “Edible” Tag for any item the player can eat in your game. More info
See in Glossary.
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 (read only), 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 (read only).|
|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).|
|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.