| jmp | JMP Data |
| jmt | JMatch Data |
| jmx | JMix Data |
| jn1 | BibExcel Journal Data |
| jnl | Ingres Journal Data |
| jnl | WinDev Log |
| jns | JANIS XML Data |
| job | MicroSim PCBoard External Job Data |
| job | USoft Job Definitions Data |
| job | VecTor5 Job Data |
| job | Windows Task Scheduler Job Object |
| jobs | VirtualDub Jobs Data |
| jod | Microsoft Jet OLEDB |
| joda | Joost Open Distribution Archive |
| jof | SmartCAM Job Operations File |
| joh | Zero 88 Jester ML Update Help Data |
| joined | HJSplit Data |
| joml | JOOB Object Modelling Language Data |
| jor | Microsoft SQL Server Journal Data |
| jos | Zero 88 Jester ML Software Update Data |
| jou | MSC Patran Journal |
| journal | Nuance Equitrac Cache |
| joz | JOSM Session Data |
| jp | Java Japanese Font Properties Data |
| jpegenx | Egis Encrypted JPEG Data |
| jpegx | Egis Encrypted JPEG Data |
| jperf | JPerf Data |
| jpgenx | Egis Encrypted JPEG Data |
| jpgs | CyberLink Power Media Player Data |
| jpgx | Egis Encrypted JPEG Data |
| jpi | Jupiter Filled Forms Data |
| jpm | Optifine JSON Part Model |
| jpn | PhotoModeler Lite Data |
| jpn | Windows Japanese Noise-word List |
| jpo | JPO Data |
