What is the UNL file format?
A .unl file is a backup copy file used for unlocking maps on Garmin GPS devices. Unlock codes can be generated using the MapSource program, which is used for managing and purchasing navigation maps. The .unl file and the codes it contains are tied to one specific Garmin device unit ID and cannot be used on multiple devices.
Map unlock codes serve as a security measure to protect purchased Garmin map content. Maps and associated license keys are stored on the device and within MapSource; .unl files provide an additional backup copy of those codes. Files are generated and managed using MapSource via its Unlock Maps function. Generated codes will only work on the device to which they are dedicated and thus cannot be transferred to other Garmin receivers.
MapSource has been replaced by Garmin BaseCamp, and modern Garmin devices use .GMA (Garmin Map Activation) files instead of .unl for map authorization. Users with older devices should not delete existing .unl files, as they may be the only backup copy of a purchased map unlock code.
Security & safety
RISK: LOWPlain text file; no execution risk. The unlock codes are device-specific and useless on other hardware. No known malware uses .unl extension.
Format details
in a nutshellPrograms that open UNL files
Windows3 apps
MapSource
Free MapSource (discontinued - last version 6.16.3) reads .unl files automatically when present in the Maps folder. Download the final version from Garmin's software archive if you have an older device. 
NotePad++ text editor
Built-in UNL files are plain text; open in any text editor to view the unlock code string (for backup reference only). 
Garmin BaseCamp
Free BaseCamp replaced MapSource; it uses .gma activation rather than .unl, but existing .unl codes on your device remain valid for that device. Technical details
deep spec| Internal format | Plain text (ASCII) |
| Magic bytes | None - plain text file with no binary header |
| Typical file size | Under 5 KB (a few lines of text) |
| Code binding | Each unlock code is cryptographically bound to a specific Garmin GPS unit ID; invalid on any other device |
| Supported OS | Windows (MapSource software) |
| Managing software | Garmin MapSource - Unlock Maps function generates and stores .unl files |
| Software status | MapSource discontinued; replaced by Garmin BaseCamp |
| Successor format | GMA (Garmin Map Activation) - used by modern Garmin devices for map authorization |
| File content | One or more Garmin-proprietary map unlock code strings tied to a device unit ID |
| Preservation note | Deleting a .unl file may permanently forfeit access to purchased map licenses on older Garmin devices |
| Encryption | Codes are device-locked by Garmin's proprietary algorithm; the file itself is plain text |
| Released | Early 2000s (with Garmin MapSource and pre-loaded map purchases) |
| Latest version | No versioning; format was static during MapSource era |
UNL conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about UNL files.
