What is the ACL file format?
An .acl file is a proprietary binary settings file used by Microsoft Office to store AutoCorrect entries - pairs of misspelled, abbreviated, or shorthand text mapped to their intended replacements. When a user types a known trigger string in Word, Excel, or PowerPoint, Office silently substitutes the stored replacement, enabling both error correction and shorthand expansion.
The format has been part of Microsoft Office since approximately Office 95 (Word 7.0, circa 1995). AutoCorrect lists are language-specific: the default US English list is named MSO1033.acl, where 1033 is the Windows LCID (Locale Identifier) for English (United States). Each configured language generates its own numbered .acl file. On Windows the files live in %APPDATA%\Microsoft\Office\; on macOS they are stored in ~/Library/Application Support/Microsoft/Office/.
Microsoft has never published the internal binary format. Community analysis identifies the signature bytes 04 01 96 00 at offset 0 and suggests a binary tree-like structure for fast lookup, but the layout remains undocumented. The file cannot be edited directly in a text editor; entries must be managed through the AutoCorrect Options dialog in any Office application.
ACL files are user-scoped and do not roam by default - organizations that need to deploy or synchronize custom AutoCorrect lists across workstations must copy the files manually or via endpoint management policy.
Security & safety
RISK: LOWACL files are data-only (text replacement rules); they cannot execute code. Risk is minimal. Receiving an ACL file from an untrusted source is unusual - the format cannot carry macros.
Format details
in a nutshell- ACL (Access Control List) - generic term - Some software exports Access Control List permissions as .acl text files; unrelated to Office AutoCorrect.
- Cubase/Nuendo AutoCorrect (audio) project files - Steinberg DAW uses .acl for certain project settings; completely unrelated to Office.
Programs that open ACL files
Windows2 apps
Microsoft Office (Word / Excel / PowerPoint)
Paid Do not open directly - manage via File > Options > Proofing > AutoCorrect Options.
Microsoft 365
Freemium ACL files are used by the installed desktop app; manage entries via Word Options > Proofing > AutoCorrect. 
macOS1 app
Microsoft Office applications
Paid Open Word/Excel/PowerPoint > Preferences > AutoCorrect to view or edit entries. Technical details
deep spec| Magic bytes | 04 01 96 00 at offset 0 (community-identified; not documented by Microsoft) |
| Byte order | Little-endian |
| Internal structure | Undocumented binary; community analysis suggests a binary search-tree-like key-value store for fast prefix lookup |
| Language scoping | One `.acl` file per language; file name encodes the Windows LCID (e.g., `MSO1033.acl` for US English, `MSO1031.acl` for German) |
| File location (Windows) | `%APPDATA%\Microsoft\Office\` (e.g., `C:\Users\<user>\AppData\Roaming\Microsoft\Office\`) |
| File location (macOS) | `~/Library/Application Support/Microsoft/Office/` |
| Typical size | 10 KB - 500 KB (grows with number of AutoCorrect entries) |
| Entry type | Key-value pairs: trigger string (misspelling or abbreviation) mapped to replacement string |
| Version compatibility | Office upgrades read and migrate `.acl` files from earlier versions; no public versioning field in the format |
| Edit method | Managed exclusively through the AutoCorrect Options dialog in Office; not directly editable as plain text |
| Roaming behavior | User-scoped; does not sync automatically across devices - manual copy or enterprise policy required for deployment |
| Platform | Windows and macOS (same binary format; different file path conventions per OS) |
| Released | circa 1995 (Microsoft Office 95 / Word 7.0) |
| Latest version | No public versioning; current format used since Office 2007+ |
ACL conversions
Community Q&A
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