Git Protocol
The git: protocol fetches packages directly from a git repository. This is useful when you need to use a version of a package that has not been published to the npm registry.
Packing
The target repository won't be used as-is - it will first be packed using pack.
To be sure the output is identical to what the linked repository would look like after being published, the packing will look at its configuration to decide which package manager to use.
In other words, the project will be packed using Yarn if there's a yarn.lock, npm if there's a package-lock.json, or pnpm if there's a pnpm-lock.yaml.
Commit pinning
You can explicitly request a tag, commit, branch, or semver tag, by using one of those keywords (if you're missing the keyword, Yarn will look for the first thing that seems to match, as in prior versions):
git@github.com:yarnpkg/berry.git#tag=@yarnpkg/cli/2.2.0
git@github.com:yarnpkg/berry.git#commit=a806c88
git@github.com:yarnpkg/berry.git#head=master
Workspaces support
Workspaces can be cloned as long as the remote repository uses Yarn (or npm, in which case npm@>=7.x has to be installed on the system):
git@github.com:yarnpkg/berry.git#workspace=@yarnpkg/shell&tag=@yarnpkg/shell/2.1.0
Not all package managers support installing workspaces from git repositories; you shouldn't rely on this feature in your dependencies field if your package is meant to be published.