| 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 |
| 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 |
| jtm | React JSX Template Method Data |
| jtp | JetForm Data |
| jtx | Microsoft Exchange ESE Log |
| jus | Jusan Fidelity License Data |
| jvdb | The Journal Volume Database |
| jvl | Jalview Launch Data |
| jvsk | jetVideo Skin Data |
| jvwr | JPEGView Creator Data |
| jvxl | Jmol Voxel File |
| jwb | JIRA Workflow Data |
| jwc | JewelCase Maker Data |
| jwk | JSON Web Key |
