| Extension |
File Type |
File Description |
| .j | Compressed | JAR Archive |
| .j | Raster Image | JPEG Image |
| .j | Developer | Java Source File |
| .j2c | Raster Image | JPEG 2000 Code Stream |
| .j2i | Game | Jazz 2 Internet Link File |
| .j2k | Raster Image | JPEG 2000 Image |
| .j2l | Game | Jazz Jackrabbit 2 Level File |
| .jad | Misc | Java Application Descriptor File |
| .jam | Audio | JAM Musical Score |
| .jam | Game | PS3 Unreal Tournament 3 Mod File |
| .jar | Executable | Java Archive File |
| .jar.pack | Compressed | Pack200 Packed Jar File |
| .jas | Raster Image | Paint Shop Pro Compressed Graphic |
| .jasper | Data | JasperReports Data File |
| .jav | Developer | Java Source File |
| .java | Developer | Java Source Code File |
| .jb2 | Raster Image | JBIG2 Image |
| .jbf | Raster Image | Paint Shop Pro Browser Cache File |
| .jbi | Data | Motoman Robot Job File |
| .jbig | Raster Image | Joint Bi-level Image Group File |
| .jbk | Backup | Juno Backup File |
| .jbr | Raster Image | Paint Shop Pro Brushes File |
| .jc | Misc | FlashGet Partial Download |
| .jc! | Misc | FlashGet Incomplete Download |
| .jcz | Web | Liquid Motion Animation |
| .jdb | Data | Symantec Endpoint Protection Update File |
| .jed | Developer | Xilinx JEDEC Programming File |
| .jef | Data | Janome Embroidery Format |
| .jfi | Raster Image | JPEG File Interchange Image |
| .jfif | Raster Image | JPEG File Interchange Format |
| .jg4 | Game | BigJig Jigsaw Puzzle |
| .jgz | Compressed | Gzipped Javascript File |
| .jhtml | Web | Java HTML Web Page |
| .jia | Raster Image | Digital Photo Navigator Album |
| .jic | Developer | JTAG Indirect Configuration File |
| .jic | Compressed | Java Icon File |
| .jif | Raster Image | JPEG Image File |
| .jiff | Raster Image | JPEG Image File Format |
| .jis | Text | Japanese Industry Standard Text |
| .jmp | Data | JMP Data File |
| .jng | Raster Image | JPEG Network Graphic |
| .jnlp | Web | Java Web Start File |
| .jnt | Data | Windows Journal File |
| .job | CAD | MetaCAM Nest Job File |
| .joboptions | Data | Adobe Joboptions File |
| .joined | Data | HJ-Split Data File |
| .jp1 | Text | Japanese (Romaji) Text File |
| .jp2 | Raster Image | JPEG 2000 Core Image File |
| .jpc | Raster Image | JPEG 2000 Code Stream File |
| .jpd | Raster Image | Joint PhotoDefiner Image |
| .jpd | Developer | Java Process Definition |
| .jpe | Raster Image | JPEG Image |
| .jpeg | Raster Image | JPEG Image File |
| .jpf | Raster Image | JPEG 2000 Image |
| .jpg | Raster Image | JPEG Image File |
| .jph | Data | JProbe Memory Snapshot |
| .jpr | Developer | JBuilder Project |
| .jpw | GIS | World File for JPEG |
| .jpx | Developer | JBuilder Project |
| .jpx | Raster Image | JPEG 2000 Image File |
| .jrprint | Data | JasperReports Print File |
| .jrs | Misc | Exchange Reserve Transaction Log File |
| .jrxml | Data | JasperReports Layout File |
| .js | Web | JavaScript File |
| .js | Executable | JScript Executable Script |
| .jse | Executable | JScript Encoded File |
| .jsf | Settings | Project64 Joystick File |
| .jsfl | Developer | Flash JavaScript File |
| .json | Developer | JavaScript Object Notation File |
| .jsp | Web | Java Server Page |
| .jspa | Web | Java Servlet Alias |
| .jspx | Web | XML Java Server Page |
| .jsx | Executable | ExtendScript Script File |
| .jt | CAD | JT Open CAD File |
| .jtf | Raster Image | JPEG Tagged Interchange Format |
| .jtp | Page Layout | Windows Journal Template |
| .jts | Video | Cyberlink AVCHD Video File |
| .jude | Data | JUDE Project File |
| .jvs | Web | JavaScript Proxy Autoconfig File |
| .jwl | Raster Image | Roxio Jewel Case File |
| .jws | Web | Java Web Services File |
| .jws | Settings | Java Workspace Settings File |
| .jxr | Raster Image | JPEG XR Image |
