Slack on a Mac keeps a cache per workspace, and never shrinks it
Slack stores caches, service worker data and downloads per workspace. Where they are, what quitting first changes, and what actually comes back.
Slack is a web browser wearing an app costume, which is why its storage behaves like a browser's rather than like a document app's. Every workspace you have joined gets its own cache, and leaving a workspace does not remove it.
Where it keeps things
du -sh ~/Library/Application\ Support/Slack/* 2>/dev/null | sort -h | tailThe folders that usually top that list:
| Folder | What it is | Comes back |
|---|---|---|
Cache and Code Cache | Page and script cache | Yes, quickly |
Service Worker | Offline data for the web app | Yes, on next sign in |
IndexedDB | Message and file metadata per workspace | Yes, resynced |
logs | Diagnostic logs | Yes, and they are small |
The part that is not cache
Files you have downloaded from Slack do not live in that folder at all. They go wherever the Slack setting points, which is your Downloads folder unless you changed it. If Slack is being blamed for space, check there too, because a year of shared decks and screen recordings adds up faster than the caches do.
du -sh ~/Downloads 2>/dev/nullClearing it without breaking anything
Slack has a built in option, which is the safe route: from the menu bar, Help, Troubleshooting, Clear Cache and Restart. It signs nothing out and rebuilds as you use it.
If you would rather do it by hand, quit Slack completely first. Removing cache folders under a running Electron app produces a rebuilt folder and a confusing size, and occasionally a corrupted session that costs you a sign in. Quitting first avoids both.
How much this is worth
Slack is rarely the largest thing on a Mac, and it is often in the top ten on a work machine with several workspaces. Treat it as one of a group: chat and meeting apps are all built the same way and all keep the same kinds of cache, so the sensible move is to check them together rather than one at a time.
The same shape of problem, measured, is in what Chrome actually stores, and the wider map of where app data lives is in your Library folder.
Common questions
Where does Slack store its cache on a Mac?
In ~/Library/Application Support/Slack, with separate Cache, Code Cache, Service Worker and IndexedDB folders. Files you downloaded from Slack are not there, they go to your Downloads folder or wherever the app's download setting points.
How do I clear the Slack cache on a Mac?
From the menu bar, Help, Troubleshooting, Clear Cache and Restart. That is the safe route because it does not sign you out. Clearing folders by hand works too, but quit Slack fully first or the app rewrites them as you go.
Will clearing Slack's cache delete my messages?
No. Messages live on Slack's servers and the local copies are a cache that resyncs. What you lose is speed on the first load after clearing, and any offline access until the app has caught up.
Why is Slack using several gigabytes?
Usually because each workspace keeps its own cache and service worker data, and leaving a workspace does not remove what it stored. A Mac signed in to four or five workspaces over a couple of years accumulates several copies of the same kinds of data.