| jrs | Microsoft Exchange Reserved Transaction Log |
| jrx | MDI DataScan Task List |
| js | Esko Automation Engine Job Sheet Data |
| jsd | Jazer Data File |
| jsd | JSDraw Data |
| jsda | Jazer Data File |
| jsdb | JumpStart Database |
| jsdraw | JSDraw Data |
| jsee | EmEditor Recorded Macro |
| jsf | Jahshaka Scene |
| jsf | Project64 Joystick Data |
| jsgf | Java Speech Grammar Format Data |
| jsk | JetAudio Skin |
| jsl | Paint Shop Pro Shape Library |
| jsml | JSim Markup Language Data |
| jsn | JetSoft Shield Now Data |
| jsobj | Opera Javascript Object |
| json | JavaScript Object Notation |
| jsonc | JSON Data with Comments |
| jsonl | JSON Lines Data |
| jsonld | JSON-LD Data |
| jsonp | JSON with Padding Data |
| jsr | Job Safety Report Definition |
| jst | Jnes Saved State |
| jsv | HyperRail 3D Coaster Design Construction Data |
| jsv | Java Structure Viewer Document |
| jtbackup | Just Type Backup File |
| jtex | Wii U Texture Data |
| jtk | IBM Infoprint Manager for AIX Job Ticket Data |
| jtl | Apache JMeter Data |
