What is the ACTION file format?
An .action file is an executable bundle used by the Automator utility available on macOS. The purpose of Automator is generating automation commands to control operating system processes without requiring users to write code. Unlike a simple file, an .action is a macOS bundle - a folder that the Finder presents as a single opaque item; right-clicking one and choosing "Show Package Contents" reveals its internal structure.
Each .action bundle stores a single, self-contained Automator action. Actions can be implemented in two ways: as a compiled Cocoa action (written in Objective-C or Swift using Xcode, with a Mach-O binary in Contents/MacOS/), or as a script action (using AppleScript, shell script, or an .applescript source stored in Contents/Resources/). A required Contents/Info.plist file declares the action's name, accepted input types, and the AMCategory key that places it in an Automator sidebar group.
Actions stored in .action files can be combined with other functions to create more advanced action combinations. Process automations created this way are enormously helpful in workflows that consist of repetitive tasks - especially those on a larger scale - as they eliminate the need for user intervention or reduce such intervention to a minimum. Assembled automation processes are saved as .workflow document files.
The .action library is built into Automator by default, so all standard functions are readily available. Advanced users can create their own action bundles from scratch using Xcode and install them for personal or system-wide use.
.action files can be saved in one of three directories for Automator to recognize them:
/System/Library/Automator- Apple system actions (do not modify)/Library/Automator- available to all users on the machine~/Library/Automator- available to the current user only
Security & safety
RISK: MEDIUMAn .action can contain executable code (a compiled binary or a shell/AppleScript), so installing one effectively adds code that Automator may run as part of a workflow - only install .action bundles from sources you trust, the same caution you'd apply to any downloaded app or script. macOS Gatekeeper and quarantine apply, and a workflow can ask for permissions (Files, Automation) when first run. Inspect a suspicious action via Show Package Contents before installing. Built-in Apple actions in System/Library are safe and should be left in place.
Format details
in a nutshellPrograms that open ACTION files
macOS3 apps
Xcode
Free For developers: open/build an Automator Action project to create or edit a Cocoa .action bundle. 
Automator
Built-in Double-click the .action; Automator offers to install it into your action library, then drag it into a workflow. Automator is included with macOS.
Finder (Show Package Contents)
Built-in Right-click the .action > Show Package Contents to inspect the Info.plist, scripts, and resources inside the bundle. Technical details
deep spec| Container format | macOS bundle - a directory the Finder presents as a single opaque file; use Show Package Contents in Finder to inspect its internals |
| Required bundle entry | Contents/Info.plist - declares action name, accepted input/output types, and AMCategory for Automator sidebar placement |
| Implementation types | Cocoa action (compiled Objective-C or Swift binary) or script action (AppleScript, shell script, or Automator XML) |
| Binary location | Cocoa actions place a Mach-O dynamic library or executable in Contents/MacOS/; script actions store their script in Contents/Resources/ |
| Input/output contract | Info.plist keys such as AMAcceptsMultipleArguments and AMProvideMultipleArguments define how data items are passed between sequential workflow steps |
| MIME type | application/octet-stream (no format-specific MIME type registered) |
| File identification | No magic bytes; identified by bundle directory structure and Automator-specific Info.plist keys, not a binary file header |
| Installation directories | /System/Library/Automator (Apple system actions), /Library/Automator (all users), ~/Library/Automator (current user only) |
| Host application | Automator - built into macOS since Mac OS X 10.4 Tiger (2005) |
| Developer | Apple Inc. |
| Architecture support | Cocoa actions built with Xcode can embed Universal Binary fat slices (x86_64 + arm64) for compatibility with both Intel and Apple Silicon Macs |
| Localization | Action UI labels, parameter names, and descriptions are localized via .lproj folders inside Contents/Resources/ |
| Action category | AMCategory value in Info.plist groups the action in an Automator sidebar section, e.g. Files and Folders, Internet, Text, or Music |
| Output document type | Assembling multiple actions into a workflow and saving produces a .workflow file - the .action bundle itself is not the saved automation |
| Released | Mac OS X 10.4 Tiger (2005), with Automator |
| Specification | developer.apple.com |
ACTION conversions
Community Q&A
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