A tool is a small program, in any language, that the Vitruvian app starts and talks to. It adds commands to the command bar, the radial menu, the Quick panel and your shortcuts.
A tool can do anything Vitruvian can. The app starts it as an ordinary program that runs as you, with every permission Vitruvian has: if Vitruvian may read the screen or control other apps, so may the tool, with no prompt of its own. The app does not limit or check what a tool does.
So you agree once, when you add a tool from its folder in Settings, on a sheet that says exactly this, and nothing asks again. Add a tool whose source you can read or whose author you trust, as you would an app. There is no list of tools to install yet: a tool comes as a folder.
The vitruvian-tool command starts a new tool, checks a folder the way the app will, and plays the app's side in a terminal.
Builds the command from source on your Mac, so macOS runs it without asking.
brew install VitruvianSoftware/tap/vitruvian-tool
One program for Apple silicon and Intel, with its checksum. It is signed ad hoc, not with an Apple Developer ID, so clear macOS's download mark once, as the guide shows.
The protocol and the kit, by version. vitruvian-tool init --template swift writes a package that depends on it.
https://github.com/VitruvianSoftware/vitruvian-sdk
Each is the SDK's own file, and the code on each page is checked by the SDK's tests.
From nothing to a working tool in ten minutes, then the manifest, every message, the limits, and how to find out why a tool does not work.
How the app and a tool talk: one JSON message per line, every message, and what each refusal means.
A tool written with the Swift kit, which init --template swift starts from.
A tool in plain Python with nothing else, which init starts from.