Progress

A cell that has something under way fills up, in whichever idiom the bar is already using:

Icons only	A bar along the screen-facing edge, where the running dots go and instead of them. An application part-way through a track is obviously running, so the bar says everything the dots would and one thing more.
Icons with labels	The button fills from the left, the way a Windows taskbar button does, leaving the icon and the name alone.

Hovering names what it is: “Music — 1:23 of 4:05”, “Downloads — Copying big.zip”.

Turn it on with Show Progress.

Three things can put a bar on a cell.

Files landing in a pinned folder

Free, automatic, and needs no permission. Pin a folder — Downloads, say — and anything being written into it shows on that cell.

The bar goes on the folder, not the app doing the writing

That is not a design preference. macOS tells an observer which file is being written, how far along it is and what kind of operation it is, but never which application is doing it. There is no way to put a download on Safari’s tile.

An application’s own Dock progress is published as AXProgressValue — unlike a badge — but it says nothing about which file or which operation, so it would not tell you what the folder cell already does.

Media progress

Music, Spotify and VLC, if you turn on Media Progress. Each one raises its own Automation prompt the first time it is asked, and a player whose prompt you refuse simply shows no bar.

Asking is the only route left. The interface the system itself uses for this is private and has needed an entitlement since macOS 15.4; on macOS 26 it loads, resolves every symbol, and then tells an ordinary application nothing at all. The players’ own scripting interfaces are public and exact, so Eskele asks them — every few seconds, not every frame, working out the seconds in between on its own.

Only these three. IINA, browsers and anything else are not supported and cannot be: a player has to expose a scripting interface to be asked, and the system-wide Now Playing interface is the private one that no longer answers.

If a media bar does not appear

The answer is usually “that player is not running” or “Automation was refused”:

open -n /Applications/Eskele.app --args --diagnose-progress
cat ~/Library/Application\ Support/Eskele/diagnose-progress.txt

Run it while something is playing, and through open rather than from a shell: macOS attributes an Apple event to the process responsible for it, so a script run from a terminal proves what the terminal is allowed to do, not what Eskele is.

A command you supply

For anything else — a build, a render, a backup, a long job in something that is not scriptable:

~/Library/Application Support/Eskele/progress.json

The file opens with worked examples, and mirrors badges.json key for key.

Key	Meaning
bundleID	An application to draw on…
path	…or the absolute path of a folder or file already on the bar
command	Run through /bin/sh as you, with a 10-second timeout
interval	Seconds between runs. 5–3600, default 30

How the number is read: a value above 1 is a percentage and 0–1 is a fraction, so 1 means finished. Add a % to be explicit.