How to Auto-Process Files Added to a Folder on Mac

A Folder Action is a folder with a job. Drop files in, and macOS runs a workflow on them automatically — convert every image to JPEG, file PDFs by date, tag everything red for review. It's the oldest trick in Automator and still one of the best, because it works while you do something else. No third-party apps, works on Ventura, Sonoma, and Sequoia.

Build the Folder Action

1. Open Automator, choose File → New, and pick Folder Action.
2. At the top of the workflow area, use Folder Action receives files and folders added to → Choose folder… and pick (or create) the folder to watch. A fresh folder like ~/Drop-Convert is better than pointing at Downloads — more on that below.
3. Drag actions in from the library. They receive every newly added file as input and run top to bottom.
4. Save (Cmd+S) with a descriptive name like Convert to JPEG. There's no app to launch afterwards — the folder is now live.

A worked example: every image becomes a JPEG

Say you constantly receive HEIC photos and screenshots in mixed formats, and everything needs to end up as JPEG in one place:

• Change Type of Images — set To Type to JPEG. Automator will offer to add a Copy Finder Items step first to preserve originals; accept it and point the copies at an Originals subfolder if you want a safety net.
• Move Finder Items — send the converted files to their real destination, like ~/Pictures/Inbox.

Drop a HEIC file into the watched folder and give it a second or two: the JPEG appears in the destination. Other useful building blocks: Rename Finder Items (add today's date to everything), Set the Label of Finder Items (auto-tag for review), and New PDF from Images.

Managing what's attached where

Right-click any folder in Finder and choose Folder Actions Setup… (look under Services at the bottom of the menu if it isn't listed directly). The dialog shows every watched folder on the left and its attached workflows on the right — this is mission control. From here you can attach existing scripts to more folders, untick one temporarily, or select and remove it entirely. The master Enable Folder Actions checkbox at the top kills or revives the whole system at once.

Saved Folder Action workflows live in ~/Library/Workflows/Applications/Folder Actions; to edit one later, open the file from there and it loads back into Automator.

Rules that save you grief

• Watch dedicated folders, not busy ones. Attaching an action to Downloads means every browser download — partial files included — gets processed. A purpose-made drop folder gives you control over what triggers it.
• Never move files into the watched folder itself as the workflow's final step — that re-triggers the action and you've built a loop.
• Undo is two clicks: right-click the folder → Folder Actions Setup… → untick or remove the workflow. The folder instantly becomes an ordinary folder again; nothing else changes.

Keep Downloads under control the same way

The most popular use for this technique is taming the Downloads folder — filing installers, archiving old files, keeping the desktop honest. There's a full walkthrough in how to clean up your Downloads folder, which pairs nicely with a Folder Action doing the boring part forever.