| jar | Java Archive |
| jbackup | The Journal Backup Archive |
| jdb | Symantec Endpoint Protection Update |
| jgz | JNode Module Package |
| jisp | Tkabber Emoticon Set |
| jma | NSRT Compressed Game ROM |
| jpa | JoomlaPack Backup Archive |
| jpa | Akeeba Multi-part Backup Archive |
| jps | Akeeba Secured Backup Archive |
| jp_ | Compressed Microsoft JPEG Image |
| jsonlz4 | Mozilla Firefox Compressed Bookmarks Backup |
| jva | Junos Firefly VM Package |
| kb2 | Kleo Backup Archive |
| kde | Kaspersky KryptoStorage Container |
| kdz | LG Smartphone Firmware Update |
| keb | Kaspersky Anti-virus Virus Bases Data |
| kgb | KGB Compressed Archive |
| kge | KGB Archiver Encrypted |
| kodi | Kodi Update Data |
| kry | Krypter Encrypted Data |
| ksp | KeyShot Package |
| kva | KVIrc Compressed Archive |
| kwt | KVIrc Theme Pack |
| kz | KuaiZip Compressed File |
| lal | Liberkey Core Update File |
| lbf | LG Phone Backup Archive |
| lbr | LU Library Archive |
| lcb | Living Cookbook Backup |
| lg | Arhangel Compressed Archive |
| lgu | LG Windows CE Device Firmware Update |
| lha | LH ARC Archive |
| lhw | LhWarp Compressed Archive |
| liz | Liberty Instruments LAUD Program Update |
| lja | ljArchive Archive |
| lks | Liberkey Installation Package |