What is the LACCDB file format?
A .laccdb file is a lock file created by Microsoft Access when a .accdb database is opened. Introduced with Access 2007, it replaced the older .ldb lock file that accompanied .mdb databases. The .laccdb file takes the same base name as its paired .accdb file and is saved in the same folder.
The file tracks concurrent users by storing fixed-width records - each record holds the Windows machine name and the Access security or user name of everyone who currently has the database open. Because of this, you can open a .laccdb in Notepad to quickly see which users have the file locked. The file contains no actual database data whatsoever.
Access creates the .laccdb automatically when the first user opens the database and deletes it automatically when the last user closes it. If the file persists after the database has been closed by all users - for example, after a crash - it is harmless and can be safely deleted from the system.
Security & safety
RISK: LOWA .laccdb is a harmless temporary text file. It carries no data and runs no code. The only caution: do not delete it while the database is actually open by someone, as that can disrupt the multi-user session. When the database is closed everywhere, a leftover .laccdb is safe to delete; Access recreates it on next open.
Format details
in a nutshellPrograms that open LACCDB files
Windows2 apps
Microsoft Access
Paid You do not open the .laccdb. Open the matching .accdb in Access; the lock file is managed automatically. 
Notepad
Built-in Only to peek inside: open the .laccdb in Notepad to read the computer/user names of who has the database open. Technical details
deep spec| File role | Temporary sidecar lock file - tracks which users currently have the paired .accdb database open |
| Format type | Plain-text fixed-width records (not a database or container format) |
| Developer | Microsoft |
| Text encoding | ASCII - stores Windows machine name and Access security/user name strings |
| Record structure | Each record is approximately 64 bytes: Windows computer name + Access user or security name of one connected user |
| Typical file size | 0 bytes when idle; grows by ~64 bytes per connected user; rarely exceeds a few KB |
| File signature (magic bytes) | None - no fixed header or magic number; the file may appear empty when no users are connected |
| Maximum users tracked | Up to 255 concurrent-user records, matching the Access database engine's concurrent-user limit |
| Creation trigger | Created automatically by Access when the first user opens the paired .accdb file |
| Deletion trigger | Deleted automatically when the last user closes the database; files left over after a crash are harmless |
| Contains database data | No - stores only user identity and machine name records; no tables, queries, or application data |
| Paired database format | .accdb (Access 2007 and later); the older .mdb format uses .ldb lock files instead |
| Platform | Windows only |
| MIME type | application/octet-stream |
| Readable without special tools | Yes - can be opened in Notepad to view the list of machine names and user names currently holding the database open |
| Released | 2007 (Access 2007, alongside the .accdb format) |
| Latest version | Tied to the Access .accdb engine; unchanged in concept since 2007 |
| Specification | learn.microsoft.com |
LACCDB conversions
Community Q&A
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