| .JAR | Java Archive File | 173 |
| .JPG | JPEG Image | 192 |
| .JS | JavaScript File | 200 |
| .JSP | Java Server Page | 259 |
| .JAVA | Java Source Code File | 192 |
| .JPEG | JPEG Image | 199 |
| .JPX | JPEG 2000 Image File | 289 |
| .JP2 | JPEG 2000 Core Image File | 271 |
| .JSPX | XML Java Server Page | 233 |
| .JNLP | Java Web Start File | 247 |
| .JSON | JavaScript Object Notation File | 195 |
| .JNT | Windows Journal File | 236 |
| .JRPRINT | JasperReports Print File | 275 |
| .JDB | Symantec Endpoint Protection Update File | 250 |
| .JPS | Stereo JPEG Image | 211 |
| .JSPF | Java Server Page Fragment | 300 |
| .JBC | Jam STAPL Byte-Code File | 225 |
| .JSF | Java Script Command File | 226 |
| .JPS | Akeeba Backup Archive | 250 |
| .JSE | JScript Encoded File | 350 |
| .JPC | JPEG 2000 Code Stream File | 200 |
| .JPR | JBuilder Project | 300 |
| .JPX | JBuilder Project | 433 |
| .J2C | JPEG 2000 Code Stream | 300 |
| .JPW | World File for JPEG | 300 |
| .JS | JScript Executable Script | 227 |
| .JBR | Paint Shop Pro Brushes File | 350 |
| .JIC | Java Icon File | 433 |
| .JIC | JTAG Indirect Configuration File | 325 |
| .J2L | Jazz Jackrabbit 2 Level File | 200 |
| .JUDE | JUDE Project File | 300 |
| .JHTML | Java HTML Web Page | 310 |
| .JWS | Java Web Services File | 275 |
| .JWS | Java Workspace Settings File | 283 |
| .JAD | Java Application Descriptor File | 189 |
| .J2I | Jazz 2 Internet Link File | 300 |
| .JC | FlashGet Partial Download | 237 |
| .JEF | Janome Embroidery Format | 197 |
| .JC! | FlashGet Incomplete Download | 250 |
| .JGZ | Gzipped Javascript File | 300 |
| .JNG | JPEG Network Graphic | 210 |
| .JSX | ExtendScript Script File | 173 |
| .JG4 | BigJig Jigsaw Puzzle | 350 |
| .JIA | Digital Photo Navigator Album | 400 |
| .JPH | JProbe Memory Snapshot | 250 |
| .JT | JT Open CAD File | 178 |
| .JMP | JMP Data File | 260 |
| .JOBOPTIONS | Adobe Joboptions File | 264 |
| .JOINED | HJ-Split Data File | 200 |
| .JRXML | JasperReports Layout File | 291 |
| .JASPER | JasperReports Data File | 178 |
| .JXR | JPEG XR Image | 279 |
| .JSFL | Animate JSFL Script File | 300 |
| .JTP | Windows Journal Template | 262 |
| .JB2 | JBIG2 Image | 333 |
| .JBI | Motoman Robot Job File | 300 |
| .JTS | Cyberlink AVCHD Video File | 300 |
| .JOB | Windows Task Scheduler Job File | 225 |
| .JDF | Adobe Acrobat Job Definition File | 300 |
| .JVSG | Video Surveillance Project | 150 |
| .JAS | Cheetah3D Model File | 317 |
| .JTV | JRiver TV File | 200 |
| .JAM | Jam STAPL File | 240 |
| .JBIG2 | JBIG2 | 200 |
| .JSS | JACOsub Subtitle File | 267 |
| .J3O | jMonkeyEngine 3D Scene | 300 |
| .JCP | JCreator Project File | 300 |
| .JAP | Nonogram Puzzle File | 214 |
| .JQZ | JQuiz File | 200 |
| .JCL | JCloze File | 350 |
| .JCW | JCross File | 300 |
| .JMT | JMatch File | 250 |
| .JMX | JMix File | 212 |
| .JMS | Masher Project | 167 |
| .JKS | Java Keystore File | 312 |
| .JCEKS | JCEKS Keystore File | 240 |
| .JST | Jnes Save State | 300 |
| .JMF | Jackhammer Project | 180 |
| .JPA | Akeeba Backup Archive | 200 |
| .JMC | JM-Crypt Encrypted File | 167 |
| .JMCX | JM-Crypt Encrypted File | 300 |
| .JSPF | JSON Playlist File | 400 |
| .JNX | BirdsEye JNX Raster Map | 250 |
| .JAS | Paint Shop Pro Compressed Graphic | 400 |
| .JTF | JPEG Tagged Interchange Format | 333 |
| .J | Java Source File | 276 |
| .JAV | Java Source File | 200 |
| .JFIF | JPEG File Interchange Format | 360 |
| .JPE | JPEG Image | 258 |
| .JBIG | Joint Bi-level Image Group File | 314 |
| .JFI | JPEG File Interchange Image | 250 |
| .JIS | Japanese Industry Standard Text | 267 |
| .J2K | JPEG 2000 Image | 233 |
| .JBK | Juno Backup File | 217 |
| .JPD | Java Process Definition | 250 |
| .JIF | JPEG Interchange Format Image | 264 |
| .JBF | Paint Shop Pro Browser Cache File | 275 |
| .JCZ | Liquid Motion Animation | 450 |
| .JPF | JPEG 2000 Image | 252 |
| .JED | Xilinx JEDEC Programming File | 250 |
| .JAM | JAM Musical Score | 400 |
| .JAM | PS3 Unreal Tournament 3 Mod File | 450 |
| .JSPA | Java Servlet Alias | 154 |
| .JPD | Joint PhotoDefiner Image | 400 |
| .JRS | Exchange Reserve Transaction Log File | 350 |
| .JSF | Project64 Joystick File | 380 |
| .JOB | MetaCAM Nest Job File | 195 |
| .JWL | Roxio Jewel Case File | 380 |
| .JNP | Java Web Start File | 283 |
| .JSXBIN | Binary ExtendScript Script File | 267 |
| .JSXINC | ExtendScript Included Script File | 350 |
| .JDC | JDownloader Links File | 350 |
| .JST | JavaServer Page Document | 400 |
| .JAM | Line 6 Device Recording | 300 |
| .JTX | ESE Transaction Log | 400 |
| .JGW | JPEG World File | 282 |
| .JPR | Fugawi Projection File | 433 |
| .JPGW | JPEG World File | 312 |
| .JA | Jet Archive | 333 |
| .JAG | Jagex Data File | 275 |
| .JL | Julia Source Code File | 260 |
| .JPG2 | JPEG 2000 Image | 283 |
| .JCLIC | JClic Project File | 400 |
| .JSH | JAWS Script Header File | 250 |
| .JSS | JAWS Script | 333 |
| .JSS | JavaScript Style Sheet File | 200 |
| .JKM | JAWS Key Map File | 225 |
| .JOY | CryENGINE Facial Editor Joystick File | 333 |
| .JNILIB | JNI Library | 267 |
| .JSD | Jazer Data File | 367 |
| .JCRYPT | JCRYPT File | 300 |
| .JTBACKUP | Just Type Backup File | 400 |
| .JGCSCS | EditPad Custom Syntax Coloring Scheme File | 450 |
| .JMV | Jnes Movie File | 300 |
| .JKB | Jedi Knight Bot File | 200 |
| .J6I | Ricoh Camera Image File | 286 |
| .JDAT | J&ASoft Data File | 200 |
| .JCR | Nonogram Puzzle File | 250 |
| .JSONLZ4 | Compressed Firefox Bookmarks Backup File | 219 |
| .JET | JET Database File | 312 |
| .JBEAM | BeamNG Vehicle Definition Format | 187 |
| .J01 | Akeeba Multi-part Backup Archive | 467 |
| .JMCP | JM-Crypt Encrypted File | 400 |
| .JMCK | JM-Crypt Key File | 350 |
| .JMCE | JM-Crypt Encrypted File | 250 |
| .JMCR | JM-Crypt Encrypted File | 400 |
| .JDP | BlackBerry JDE Application Project | 467 |
| .JSL | Corel PaintShop Pro Shape Library | 225 |
| .JDR | IROAD Dash Cam Video File | 257 |
| .JVSGZ | Compressed Video Surveillance Project | 225 |
| .JPG-LARGE | Large JPEG Image | 257 |
| .JNR | JoinNet Recording File | 450 |
| .JLR | Juliar Source Code File | 160 |
| .JTD | JustSystems Ichitaro Document | 325 |
| .JAP | jAlbum Project Settings File | 400 |
| .JSD | HP JetSuite Document | 400 |
| .JUK | Juka Source Code File | 200 |
| .JAG | Atari Jaguar Game ROM | 400 |
| .JBR | Motoman Robot Related Job File | 400 |
| .JSL | JMP Script | 233 |
| .JWPUB | Jehovah's Witnesses Publication File | 267 |
| .J | JPEG Image | 375 |
| .JVS | JavaScript Proxy Autoconfig File | 475 |
| .JIFF | JPEG Image File Format | 333 |
| .JP1 | Japanese (Romaji) Text File | 317 |
| .J | JAR Archive | 320 |
| .JAR.PACK | Pack200 Packed Jar File | 210 |
| .JRZ | PSP Game Data File | 300 |
| .JRTF | JAmes OS Rich Text File | 400 |
| .JBMP | JAmes OS Bitmap Image | 500 |
| .JTX | XPS Document | 500 |
| .JTX | Jrju Text File | 300 |
| .JIGSAW | Jigsaw Explorer Save File | 300 |
| .JO-7Z | jo Audio File | 500 |
| .JO | jo Audio File | 300 |
| .JPN | Windows Japanese Noise-Word List File | 362 |
| .JSH | Jsh Script | 500 |
| .JRC | PCjr Cartridge ROM File | 267 |
| .JARVIS | Jarvis Subscriber File | 243 |
| .JSDA | Jazer Data File | 500 |
| .JAP | Japanese Nintendo 64 Game ROM | 333 |
| .JOE | JOE Document | 400 |
| .JAC | JaStaCry Encrypted File | 300 |
| .JBG | Joint Bi-level Image Group File | 350 |
| .J64 | Atari Jaguar Game ROM | 500 |