| jdl | gLite Job Description Language File |
| jds | JDataStore Database |
| jdsu | ACTIX Analyzer JDSU Data |
| jdt | Accelio Capture Classic Filler Data |
| jdx | JSpell Dictionary Data |
| jdx | JCAMP-DX Format Data |
| jeb | PENSIM Output |
| jed | Xilinx JEDEC Data |
| jedec | Xilinx JEDEC Data |
| jef | Janome Embroidery Data |
| jeff | Java Explanation Facility Framework Data |
| jem | Optifine JSON Entity Model |
| jet | California JET Data |
| jfd | FormWare Job Definition |
| jga | John GBC Saved State |
| jgl | QWS3270 PLUS Session Layout |
| jgp | QWS3270 PLUS Session Parameter File |
| jgs | QWS3270 PLUS Script File |
| jhd | WCAD01 Job Information Data |
| jhm | JavaHelp Map |
| jib | Sam2p JIB File |
| jjf | FlashJester Jugglor Data |
| jks | Java Key Store |
| jlb | JDiveLog Logbook File |
| jlk | JET 3270 License Key Data |
| jlm | ILOG JViews License Manager Keys Data |
| jlr | JetAudio Lyric Data |
| jlt | HP SmartStream Print |
| jm3 | BlastMetriX 3D Data |
| jmf | Job Messaging Format File |
| jmp | JMP Data |
| jmt | JMatch Data |
| jmx | JMix Data |
| jnl | WinDev Log |
| jnl | Ingres Journal Data |