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Creating and managing Packages

Netherlands3D is a framework where you, as developer, can pick the functionality that you need from a series of packages. This guide will empower you to develop your own packages by providing step-by-step instructions how you can create your own package, release it and last, but not least, publish it to OpenUPM.

Variables / Placeholders

Before we get started, let's define some terms as if they were variables. This documentation and the template files in the Gist mentioned in the chapter Creating a new package uses various placeholders. These can recognized as they are between brackets, for example {NAME}.

This table provides an overview of them and their meaning.

Name Explanation Example
NAME The name of the code repository, this is usually the DISPLAY_NAME in PascalCase. It is recommended to limit the name to two words, if more words add clarity than that takes precedence. PeriodicSnapshots
PACKAGE_NAME The package name as known in the package manager and/or package.json; always starts with eu.netherlands3d. and followed by the display name -or similar- in kebab-case eu.netherlands3d.periodic-snapshots
DISPLAY_NAME The human-readable name of a package, shown in the README or in the Package Manager Periodic Snapshots
REPOSITORY_NAME Alias of NAME, used to make explicit that we want the repository name there. PeriodicSnapshots
VERSION The version number in the package.json, according to SemVer. Important: contrary to the git tag, this does not start with a letter v 1.0.1
DESCRIPTION A single-line short description describing the package, can also be used on Github as the description for the repository This package provides the means to do take a series of snapshots for specific moments throughout the year.
LONG_DESCRIPTION The description of the package detailing what it is used for.
USAGE_INFORMATION Documentation how to use this package. See existing packages for examples
NOTE One or more entries in the CHANGELOG -according to Keep A Changelog- describing what has been added, changed, removed or deprecated in a package

This vocabulary and their definitions will help to have a consistent experience when working with packages.

Creating a new package

When creating a new package, it is recommended to first create it as an embedded package in the Netherlands3D twin project. This will help to prototype and experiment until the point where it is stable enough to be distributed.

This can be done using the following steps:

  1. Clone the Netherlands3D Twin project, located at

  2. Make sure Unity is not open while performing the following steps; it generally tends to crash when it updates while setting up a package.

  3. Create a directory for your embedded package in the Packages folder.


    The directory name MUST follow the structure eu.netherlands3d.[name] where name is in lower-case kebab-case.

  4. Copy the template files, located at, and fill in the placeholders.

  5. Set up the package according to the following recommended directory structure:

  6. Start Unity and allow for it to install the new package, you should see your new package in the "Installed Packages" section of the Package Manager with the tag Custom behind the name.

  7. When you want to add Scripts to this package: Make sure you have created the folder Runtime\Scripts as a location to store them and add an Assembly Definition with the name {PACKAGE_NAME}.Runtime.

Promoting an embedded package

It takes time and effort to get a package into a usable and moderately stable condition. Because of this the recommended way of working is to first create an embedded package in the Twin project -like an incubator project- and once it is moderately stable: promote it to its own repository.

Promoting an embedded package is done by one of the project maintainers -if not alone for the fact that a repository needs to be made- and follows the following sequence of steps:

  1. Create a repository whose name matches the {NAME} placeholder, thus a PascalCase representation of the human-readable name.

  2. Move all files from the Packages\{PACKAGE_NAME} folder in the Twin repository to the newly made repository's root folder

  3. Check and adjust, at least, the URL's for the LICENSE, README and CHANGELOG in the package.json.

  4. Release and publish the promoted package, see the chapters on releasing and publishing for the involved steps.

  5. In the Twin project, add a reference to {PACKAGE_NAME} to the package.json or install the package through the package manager.


    After a package is added to OpenUPM for the first time, it can take between 30 and 60 minutes for it to show up in the package listing.

Once a package is promoted, you can no longer edit it as part of the Twin project; in the next chapter Changing a Package it is described how you can change a promoted package without all too much hassle.

Changing a package

To be written

Releasing a package

When you want to release a new version of a package you generally go through the following steps:


Before releasing, make sure you have tested your package in the Twin -or another Netherlands3D-based project- installed as a local package.

Especially important is:

  • verifying that the correct dependencies are set and installed
  • that the Assembly Definition can be used and
  • that the Assembly Definition does not depend on Assembly Definitions that are not a dependency of your package, especially Netherlands3D.Core.Runtime should be avoided

Failure to do so may cause extra work because once a package is released, it is impossible to change something in the release and a new release must be made.

  1. Go to the repository of your package. If there is none: see the chapter on Promoting an embedded package and do that first.

  2. Ensure the version number in the package.json is updated

  3. Check the

  4. Does it contain all changes since the last version?

  5. Is the top-entry [Unreleased]? Fill in the new version number and add a date, see:

  6. Ensure any changes in the above are in the main branch

  7. Go to "Releases" on Github ({NAME}/releases) and

  8. Draft a new release Draft new release

  9. Click on "Choose a tag"
  10. Enter the version number from the package.json with a preceding letter v, for example: v1.0.1.
  11. Click on the option "Create new tag: v{VERSION} on publish"
  12. (optional) Add a release title and description
  13. Click on the button "Publish Release"

Once a new release/tag has been made, your new release of your package is all set! If it has already been published on OpenUPM before, no further action is needed. OpenUPM will automatically pick up on the new tag and make the new version available.

When the package has not been published on OpenUPM yet, now is a good time to do it.

Publishing a package on OpenUPM

When a package is released for the first time, it needs to be published by registering it on OpenUPM.


Before publishing, make sure you have tested your package in -or another Netherlands3D-based project- installed as a local package.

Especially important is:

  • verifying that the correct dependencies are set and installed
  • that the Assembly Definition can be used and
  • that the Assembly Definition does not depend on Assembly Definitions that are not a dependency of your package, especially Netherlands3D.Core.Runtime should be avoided

Failure to do so may cause extra work because once a package is published, it is inconvenient to unpublish it or change publication details such as the name.

To do so, you can take the following steps:

  1. Go to

  2. Click on the "+" button in the menu bar to add a new package Screenshot of OpenUPM showing add button

  3. Fill out the Github repository name in the intended field and click on "Go". Screenshot of OpenUPM where repository can be submitted A form expands where you can verify the package name, ReadMe location and more

  4. Enter your github username in the "Discovered by" field; this is used to base a fork of OpenUPM from and add the package as a pull request.


    The section "Advanced" is for advanced use when multiple packages are hosted in the same repository; at the moment this method is not recommended and as such that part of the submission form can be skipped

  5. Check the "Promotion" section if the package fits any of these categories, and check these.

  6. Click on the "Verify Package" button, all other fields can be left unchanged.

As soon as the steps above have completed, you are asked to fork the OpenUPM repository and to commit these changes in a feature branch. At this point you can use the "Create pull request" button to create a pull request to OpenUPM.


If this is your first time submitting a package to OpenUPM, the maintainer of OpenUPM needs to approve the Pull Request manually; this is generally done within 24 hours. Any subsequent pull requests will be automatically merged.

After the pull request is merged, it will take 30 to 60 minutes for OpenUPM to add the package to the registry.


Can I depend on the Netherlands3D.Core.Runtime assembly?

At time of writing, this assembly is within the code of the skeleton; meaning that this dependency only works when the package is used within a project that is based on this skeleton. This can be a problematic dependency since we are actively working on moving the contents of this skeleton into components.

Because of the above, it is not recommended for a published package to depend on the Netherlands3D.Core.Runtime assembly.

If code from this assembly is needed, it is recommended to extract this code into another package that you can depend on or duplicate it into your own package until such a package can be made.

For more information on this, see the question Can I depend on Assemblies that are not in my own package?.

Can I depend on Assemblies that are not in my own package?

You sure can! As long as these assemblies are in a package that is published in a Unity Package Registry such as OpenUPM, and that you have added that package as a dependency to your package.json file.

If you add an assembly whose package cannot be included in your package.json -either because it is not a package or a git-based package- then you will need to add installation instructions in the README. Without these instructions, any user of the package will have a missing assembly -and thus errors- without knowing how to fix it.

One of the packages does not show up in the Package Manager after publishing

Have you checked the minimum unity version in the package.json? If the minimum version is newer than your installed version, it will not be visible.

Why OpenUPM and not add packages through a Git URL?

Good question! When you add packages through a Git URL you lose certain features that packages hosted on a registry do have. This includes but is not limited to:

  1. Unable to update to a new version: when you use a Git tag/release, then you need to uninstall and reinstall the package when a new becomes available instead of just using the Update button.

  2. Git-url based packages cannot be used as dependencies: this means that if a package depends on another, with git urls you need to manually install the correct dependencies and face possible version conflicts with newer versions.