What watched folders do

Most of what a template does happens in the moment it is deployed. A watched folder is the part that carries on afterwards: an Inbox that renames whatever you drop into it, a Deliverables folder that files images by kind, a Shoot folder that strips location data before anything leaves the studio.

A watched folder is an ordinary folder on disk. Prefab does not own it, hide it or move it. It watches for files arriving in it and applies the rules you attached to that folder in the template.

Turning an action into a rule

Rules are built in the template, not in the folder. Open the template, add an action to the folder you want watched, and under When It Runs choose Watch the folder instead of On deploy. The action becomes a rule that runs on files rather than on the folder. See Actions for how actions are attached in the first place.

An action in the template editor with the Watch the folder trigger selected and a Which files field below it — Choosing Watch the folder turns an action into a rule, and Which files decides what it acts on.

Which files takes a list of extensions, typed with or without dots: png jpg heic. Leave it empty and the rule acts on every file. One folder can carry as many rules as you like, and they run in the order they are attached, each acting on the file as the previous rule left it.

Deploying the template creates the folder as usual but does not run these rules. It registers the folder instead, and from that point on the rules apply to files that land in it. Deploying the same template over the same folder again replaces that registration rather than watching the folder twice.

Files land with the names the camera gave them, and are renamed a moment later by the rule the template carried.

Prefab has to be running

Nothing is renamed, moved or converted while Prefab is quit

Watching happens inside the app. Files that arrive while Prefab is closed are left exactly as they are at the time. Keep Keep running in menu barKeep running when the window closes switched on in Settings ▸ General, so closing the window leaves Prefab running rather than quitting it.

Launching Prefab is also a catch-up. Every watched folder that is not paused is swept once at launch, and anything that arrived in the meantime is handled then. After that the folder is watched live.

If you would rather deal with a backlog yourself, Apply Rules to Existing Files… in the menu barnotification area shows you what would change and waits for you to confirm it. See Managing and undoing.

The rules are frozen at deploy

What gets registered is a copy of the rules as they stood on the day of the deploy, not a live link back to the template. Editing the template later changes what your next deploy does. A client folder made six months ago goes on behaving the way it always has.

The placeholder values are frozen for the same reason. A rule that renames files to {{project_name}}-{{counter:3}} keeps using the project name you typed at deploy time, because there is nobody to ask at two in the morning when a file lands.

To give an existing folder your edited rules, deploy the template over that same folder again. The new registration replaces the old one, and you are asked for the placeholder values again.

Files that are still arriving

Renaming a download halfway through corrupts it, so nothing is touched until it has clearly finished. Prefab checks several things, in this order:

A file stored in the cloud and not downloaded yet, an iCloud or Dropbox placeholder, is skipped rather than pulled down.
A file whose writer is publishing progress, which is what draws FinderFile Explorer's own progress indicator, is left until that progress reaches the end.
A part-downloaded file with a temporary extension is skipped: .crdownload, .part, .download, .partial, .opdownload, .tmp, .temp, .swp. The finished file arrives under its real name and raises its own event.
A file with nothing in it yet counts as still arriving, however long it stays empty.
Anything else has to hold the same size for two seconds before it counts as settled.

Hidden files and lock files are never touched, whatever a rule's Which files list says. That means anything beginning with a dot, and Office's ~$ lock files.

Files that were already sitting in the folder are judged more directly: if nothing has written to one for ten seconds, it is ready now.

Subfolders, and files already handled

Watching is recursive. A file dropped three levels down is seen the same way as one dropped at the top. That means rules which file things away into subfolders can see their own work, so Prefab marks each file with the rules that have handled it.

That mark is why the same rules do not run on the same file twice. Change the rules and they run again. Change the file and they run again only if a rule asked for it, with Also when a file is edited - without that, every save would give the file a new number.

If a watched folder sits inside another watched folder, the innermost one's rules are the ones that apply.