Logic Fails the API Condition

"No documented way in means no sidecar. Logic doesn't fail the test by a little — it fails it at the door."

The Obvious Candidate

Logic Pro is the natural first guess for a host: it does music production overwhelmingly well (condition 1), and it's a serious tool serious musicians live in (condition 3 is plausible for many). But the sidecar idea dies on condition 2 — the extension API — and it dies hard. There is no UXP-equivalent for Logic. Nothing lets an outside program read and drive a Logic project.

Every 'API' Logic Has, and Why Each Fails

Logic Pro extension surface     verdict
---------------------------     -------
Scripter (MIDI-plugin JS)       MIDI sandbox only -- can't read the project
AppleScript                     threadbare; not a real automation surface
.logicx bundle                  proprietary; not a documented format
Audio Units (AU)                signal processing only -- not project access

Each of these is a partial door that turns out to be a wall. Scripter runs JavaScript, but only inside a MIDI effect — it can't see the project, the arrangement, or the audio. AppleScript support exists on paper but is too thin to drive a real workflow. The .logicx project bundle is an undocumented proprietary format. Audio Units process signal; they don't expose the project. Add them all up and there is still no way to read or drive a Logic project from the outside.

Condition 2 Is Binary

This is what makes Logic instructive: conditions 1 and 3 can be 'sort of' true and you can argue about degree, but condition 2 is binary. Either there's a real, documented extension API or there isn't — and for Logic, there isn't. A Logic sidecar is not 'hard to build' or 'limited.' It is not buildable. That single missing condition ends the conversation before residency or value ever come up.

Code

Logic's extension surfaces — every door is a wall·text

Logic Pro extension surface     verdict
---------------------------     -------
Scripter (MIDI-plugin JS)       MIDI sandbox only -- can't read the project
AppleScript                     threadbare; not a real automation surface
.logicx bundle                  proprietary; not a documented format
Audio Units (AU)                signal processing only -- not project access

=> No way to read/drive a Logic project from outside.
=> Sidecar: NOT BUILDABLE (condition 2 fails at the door).

Exercise

For a host you'd like to extend, list every 'extension surface' it advertises (scripting, plugins, file formats, automation). For each, ask the one hard question: can it read and drive the host's actual document/project from outside? If every surface stops short of that, you have a pile of partial doors and no real API.

Hint

Plugins that only process a stream (audio, MIDI) almost never expose the document. Scripting that's 'supported' but undocumented is usually a wall. The real test is always 'can I read the project from outside?'