| .X | DirectX Model File | 178 |
| .X | Lex Source Code File | 238 |
| .X32 | Adobe Xtra File | 231 |
| .X3D | Xara3D Project | 200 |
| .X3F | SIGMA X3F Camera RAW File | 307 |
| .X3G | 3D Print File | 230 |
| .X4K | XML4King Configuration File | 233 |
| .X64 | Commodore 64 Disk Image | 250 |
| .X86 | Linux Executable File | 225 |
| .X86_64 | 64-bit Linux Executable File | 200 |
| .XA | The Sims Audio File | 256 |
| .XA | PlayStation Audio File | 238 |
| .XA | GEAR CD/DVD Disc Image | 300 |
| .XADD | Expression Web Add-in | 400 |
| .XAF | 3ds Max XML Animation File | 180 |
| .XAF | Cal3D XML Animation File | 400 |
| .XAF | Affirm Deposition Transcript | 400 |
| .XAIML | XAIML Chatterbot Database File | 500 |
| .XAL | Exient Asset List File | 300 |
| .XAML | XAML File | 250 |
| .XAMLX | Visual Studio Workflow Service File | 250 |
| .XAN | Worms Map File | 233 |
| .XAP | Silverlight Application Package | 195 |
| .XAP | XACT Project | 204 |
| .XAPK | Compressed Android Package File | 176 |
| .XAPPL | Spoon XML Application Configuration File | 150 |
| .XAR | Xara Xtreme Drawing | 217 |
| .XAR | Extensible Archive Format File | 275 |
| .XAR | Microsoft Excel Auto-Recovery File | 260 |
| .XAS | Pro/ENGINEER Assembly Instance Accelerator File | 200 |
| .XBA | OpenOffice Basic Module File | 325 |
| .XBAP | XAML Browser Application File | 225 |
| .XBC | SMART Notebook File | 233 |
| .XBD | DocuWorks Binder File | 267 |
| .XBDOC | Xiosis Scribe Document | 367 |
| .XBE | Xbox Executable File | 167 |
| .XBEL | XBEL Bookmarks File | 217 |
| .XBF | XAML Binary File | 239 |
| .XBK | XenServer Backup File | 300 |
| .XBK | SMART Notebook File | 367 |
| .XBL | Extensible Binding Language File | 300 |
| .XBM | X11 Bitmap Graphic | 278 |
| .XBMML | Braille Music Markup Language File | 267 |
| .XBPLATE | Xiosis Scribe Template | 350 |
| .XBRL | XBRL Document | 250 |
| .XBSAV | Mass Effect 2 Xbox Saved Game | 250 |
| .XBT | SMART Notebook Template File | 400 |
| .XCAPPDATA | Xcode App Data File | 300 |
| .XCARCHIVE | Xcode Archive | 317 |
| .XCCOLORTHEME | Xcode Color Theme File | 400 |
| .XCCONFIG | Xcode Configuration Settings File | 250 |
| .XCCRASHPOINT | Xcode Crash Point File | 450 |
| .XCDATAMODEL | Xcode Core Data Model File | 400 |
| .XCDATAMODELD | Xcode Core Data Model File | 250 |
| .XCF | GIMP Image File | 212 |
| .XCI | NX Card Image File | 222 |
| .XCODE | Xcode Project | 220 |
| .XCODEPLUGIN | Xcode Plug-in | 300 |
| .XCODEPROJ | Xcode Project | 326 |
| .XCPLUGIN | Xcode Plug-in | 400 |
| .XCPLUGINDATA | Xcode Plug-in Data File | 300 |
| .XCSCHEME | Xcode Scheme File | 275 |
| .XCSL | CineStyle Color Correction File | 500 |
| .XCSNAPSHOTS | Xcode Snapshot | 300 |
| .XCT | XVI32 Character Conversion Table File | 325 |
| .XCU | OpenOffice.org Configuration File | 400 |
| .XCWORKSPACE | Xcode Workspace File | 240 |
| .XDB | Symantec Virus Database File | 320 |
| .XDB | PowerDesigner Database Definition File | 400 |
| .XDF | Microsoft Machine Learning Server Data File | 250 |
| .XDI | WinArchiver Extended Disc Image File | 233 |
| .XDL | XML Schema File | 400 |
| .XDL | Oracle Expert Definition Language File | 337 |
| .XDNA | DNA Strider Sequence File | 200 |
| .XDP | XML Data Package | 373 |
| .XDR | XML-Data Reduced File | 211 |
| .XDS | DS Game Maker Project File | 433 |
| .XDS | LcdStudio Design File | 450 |
| .XDW | Fuji Xerox DocuWorks File | 304 |
| .XEF | WinAce Encrypted File | 350 |
| .XEF | eManager Form Data | 250 |
| .XEJ | Expression Encoder Job File | 350 |
| .XEL | Expression Encoder Live Encoding File | 320 |
| .XEM | PowerDesigner Model definition File | 179 |
| .XEM | eManager Metered Units | 173 |
| .XEN | Guitar Hero III Data File | 286 |
| .XENSEARCH | XenCenter Saved Search File | 400 |
| .XEP | eManager File Packaging Information | 300 |
| .XER | Primavera P6 Project File | 205 |
| .XES | eManager Skins Definition | 219 |
| .XESC | Expression Encoder Screen Capture File | 273 |
| .XET | eManager Process Definition | 300 |
| .XEV | eManager Auto-Update File | 250 |
| .XEX | Xbox 360 Executable File | 217 |
| .XEZ | eManager Template Package | 256 |
| .XFACE | X-Face Image | 400 |
| .XFB | Xserve RAID Firmware Binary File | 300 |
| .XFD | XFD File | 255 |
| .XFD | FormFlow 99 Form Data File | 288 |
| .XFDF | Adobe Acrobat XFDF File | 307 |
| .XFDL | XFDL File | 260 |
| .XFL | Animate Movie Archive | 360 |
| .XFLOW | FlowExchange Data File | 300 |
| .XFN | Ventura Printer Font | 300 |
| .XFO | XSL-FO Formatted Form | 300 |
| .XFR | iProcess Process Definition File | 200 |
| .XFS | eRacer Sound File | 200 |
| .XFT | Adobe Form Designer 5.0 File | 200 |
| .XFT | ChiWriter Printer Font | 350 |
| .XGDW | GDevelop Extension File | 200 |
| .XGML | Graph Modeling Language XML File | 250 |
| .XGMML | XGMML Graph File | 350 |
| .XGP | Xfire Game Patcher File | 500 |
| .XGS | XACT Global Settings File | 250 |
| .XGT | Exient Texture File | 367 |
| .XHT | XHTML File | 250 |
| .XHTM | Extensible Hypertext Markup Language Document | 229 |
| .XHTML | Extensible Hypertext Markup Language File | 290 |
| .XI | Fasttracker 2 Extended Instrument File | 450 |
| .XIB | Interface Builder File | 329 |
| .XIF | ScanSoft Pagis File | 262 |
| .XIP | macOS Signed Archive | 220 |
| .XISE | Xilinx ISE Project File | 252 |
| .XIZ | ZynAddSubFX Instrument File | 200 |
| .XL | Microsoft Excel Spreadsheet | 226 |
| .XLA | Microsoft Excel Add-In File | 278 |
| .XLAM | Microsoft Excel Macro-Enabled Add-In | 218 |
| .XLB | Microsoft Excel Toolbar Settings File | 300 |
| .XLB | OpenOffice.org Module Information File | 400 |
| .XLC | Microsoft Excel Chart | 225 |
| .XLD | Microsoft Excel Database | 240 |
| .XLE | Levelogger Software XML Data File | 200 |
| .XLF | XLIFF Document | 229 |
| .XLGC | ExpressK Database File | 400 |
| .XLIFF | XLIFF Localization File | 200 |
| .XLK | Microsoft Excel Backup File | 267 |
| .XLL | Microsoft Excel Add-In File | 255 |
| .XLM | Microsoft Excel Macro | 200 |
| .XLMV | Xunlei Movie File | 300 |
| .XLNK | XML Shortcut File | 300 |
| .XLOG | WeChat Log File | 225 |
| .XLR | Works Spreadsheet | 237 |
| .XLS | Microsoft Excel Spreadsheet (Legacy) | 209 |
| .XLSB | Microsoft Excel Binary Spreadsheet | 220 |
| .XLSHTML | Microsoft Excel HTML Spreadsheet | 250 |
| .XLSM | Microsoft Excel Macro-Enabled Spreadsheet | 211 |
| .XLSMHTML | Microsoft Excel MIME HTML Spreadsheet | 360 |
| .XLSX | Microsoft Excel Spreadsheet | 210 |
| .XLT | Microsoft Excel Spreadsheet Template (Legacy) | 235 |
| .XLTHTML | Microsoft Excel HTML Spreadsheet Template | 400 |
| .XLTM | Microsoft Excel Macro-Enabled Spreadsheet Template | 214 |
| .XLTX | Microsoft Excel Spreadsheet Template | 275 |
| .XLV | Microsoft Excel Visual Basic Module | 200 |
| .XLW | Microsoft Excel Workbook | 400 |
| .XLW | Microsoft Excel Workspace | 383 |
| .XM | Fasttracker 2 Extended Module | 300 |
| .XMA | Xbox Media Audio File | 340 |
| .XMAP | XMind 2007/2008 Workbook | 450 |
| .XMB | Age of Empires Game Data File | 233 |
| .XMB | X-Wing Mission Briefing File | 225 |
| .XMCD | Mathcad Worksheet File | 273 |
| .XMCDZ | Mathcad Compressed Worksheet File | 200 |
| .XMCT | Mathcad XML Worksheet Template | 357 |
| .XMD | Extended Media Disc Image | 375 |
| .XMD | Bitdefender Plugin File | 254 |
| .XMD | ExamSoft Answer File | 367 |
| .XMDX | ExamSoft Answer File | 277 |
| .XMF | Cal3D XML Mesh File | 221 |
| .XMF | Extensible Music File | 325 |
| .XMF | GameJack Disc Image File | 433 |
| .XMI | XML Metadata Interchange File | 317 |
| .XMI | Extended MIDI File | 400 |
| .XMIND | XMind Workbook File | 257 |
| .XML | XML File | 230 |
| .XML | Cinelerra Video Project | 266 |
| .XML.KFL | Microsoft Outlook Known Feed List | 400 |
| .XMLFF | XML Flat File | 250 |
| .XMLPER | LeCroy Binary Waveform File | 300 |
| .XMM | 3ds Max XML Animation Map File | 333 |
| .XMMAP | MindManager XML Map File | 360 |
| .XMP | Extensible Metadata Platform File | 250 |
| .XMP | XMind Markers Package | 300 |
| .XMPZ | Miradi XML Project File | 500 |
| .XMS | Music Studio Project | 200 |
| .XMS | XMS-Tracker Music Module | 400 |
| .XMT | XMind Template | 150 |
| .XMU | Expressive Music Container File | 300 |
| .XMV | Xbox Media Video File | 260 |
| .XMWX | ExamSoft Working File | 329 |
| .XMZ | FastTracker 2 Extended Module | 229 |
| .XMZX | ExamSoft Exam File | 277 |
| .XNB | XNA Game Studio Binary Package | 249 |
| .XNC | Exchange NC File | 400 |
| .XNK | Exchange Shortcut | 240 |
| .XNT | QuarkXPress Extension File | 300 |
| .XOF | Reality Lab 3D Image File | 300 |
| .XOJ | Xournal Notebook | 300 |
| .XOJO_BINARY_MENU | Xojo Binary Menu File | 300 |
| .XOJO_BINARY_PROJECT | Xojo Binary Project File | 300 |
| .XOJO_BINARY_TOOLBAR | Xojo Binary Toolbar File | 350 |
| .XOJO_BINARY_WINDOW | Xojo Binary Window File | 450 |
| .XOJO_MENU | Xojo Menu File | 300 |
| .XOJO_PROJECT | Xojo Project File | 350 |
| .XOJO_TOOLBAR | Xojo Toolbar File | 400 |
| .XOJO_WINDOW | Xojo Window File | 400 |
| .XOJO_XML_MENU | Xojo XML Menu File | 333 |
| .XOJO_XML_PROJECT | Xojo XML Project File | 267 |
| .XOJO_XML_TOOLBAR | Xojo Toolbar File | 400 |
| .XOJO_XML_WINDOW | Xojo XML Window File | 383 |
| .XOL | Swiss Map Overlay | 300 |
| .XOL | PowerDesigner Object Language File | 300 |
| .XOM | Worms 3D Object File | 167 |
| .XOML | Windows Workflow File | 267 |
| .XOPP | Xournal++ Notebook | 300 |
| .XOPUS | Exient OPUS File | 300 |
| .XP | Fastracker 2 Pattern | 283 |
| .XP | XPilot Map | 367 |
| .XP2 | XPilot NG | 467 |
| .XP3 | KiriKiri Package File | 182 |
| .XP4 | KiriKiri Package | 350 |
| .XPADDERCONTROLLER | Xpadder Controller Profile | 214 |
| .XPD | XML Pipeline Document | 233 |
| .XPD | PlayStation Store PSP License File | 169 |
| .XPDL | XPDL Module | 300 |
| .XPF | LMMS Preset File | 208 |
| .XPG | Autoplay Media Studio Exported Page | 257 |
| .XPI | Cross-platform Installer Package | 187 |
| .XPJ | RoboHelp HTML Project File | 250 |
| .XPJ | Micro Planner X-Pert Project File | 400 |
| .XPK | WWE RAW Model File | 197 |
| .XPL | LcdStudio Playlist File | 300 |
| .XPL | Little Snitch Configuration File | 400 |
| .XPLL | Pull-Planner Data File | 450 |
| .XPM | X11 Pixmap Graphic | 183 |
| .XPM | Micro Planner Manager File | 450 |
| .XPP | X++ Source Code File | 250 |
| .XPR | Pro/ENGINEER Part Instance Accelerator File | 287 |
| .XPR | SyncRO Soft oXygen XML Editor Project | 350 |
| .XPR | PressIt Disc Label | 400 |
| .XPR | Microsoft Expression Design Graphic | 400 |
| .XPS | XML Paper Specification File | 236 |
| .XPT | Mozilla Firefox Component | 222 |
| .XPT | SAS Transport File | 250 |
| .XQ | XQuery File | 267 |
| .XQL | XML Query Language File | 300 |
| .XQM | XQuery Module | 300 |
| .XQT | SuperCalc Macro File | 260 |
| .XQUERY | XQuery Source Code File | 400 |
| .XQY | XQuery Source File | 214 |
| .XR | Xuver 3D Scene File | 250 |
| .XRB | XMind Resource Bundle | 233 |
| .XRDML | XRDML Data File | 256 |
| .XRF | Cal3D XML Materials File | 367 |
| .XRFF | Extensible Attribute-Relation File Format | 300 |
| .XRM-MS | Microsoft Security Certificate | 286 |
| .XRNS | Renoise Song File | 225 |
| .XRP | RationalPlan Project File | 300 |
| .XRY | XRY Data File | 300 |
| .XS | Age of Empires 3 Map AI Generator | 200 |
| .XSB | XACT Sound Bank | 345 |
| .XSB | XML Schema Binary File | 250 |
| .XSC | Visual Studio Dataset Internal Info File | 275 |
| .XSD | XML Schema Definition | 208 |
| .XSF | InfoPath Form Definition File | 344 |
| .XSF | Cal3D XML Skeleton File | 400 |
| .XSI | Softimage XSI 3D Image | 200 |
| .XSIADDON | Softimage Add-on File | 233 |
| .XSIG | XAdES XML Signature File | 400 |
| .XSL | XML Style Sheet | 258 |
| .XSLIC | XenServer License File | 240 |
| .XSLT | XSL Transformation File | 325 |
| .XSN | InfoPath Form Template File | 279 |
| .XSP | Kodi Smart Playlist File | 300 |
| .XSPF | XSPF Playlist File | 246 |
| .XSS | XML Style Sheet | 233 |
| .XST | WebSphere Query Template | 267 |
| .XSVF | Xilinx Serial Vector Format File | 150 |
| .XSX | Visual Studio XML Schema Layout File | 246 |
| .XT | Xdebug Trace File | 224 |
| .XT | Fastracker 2 Track | 400 |
| .XTB | Angular Translation File | 400 |
| .XTBL | XTBL Ransomware Encrypted File | 260 |
| .XTG | Extensible TreeGraph File | 300 |
| .XTL | Vietcong Data File | 500 |
| .XTM | CmapTools Exported Topic Map | 200 |
| .XTM | Xtremsplit Data File | 400 |
| .XTODVD | ConvertXtoDVD Project File | 350 |
| .XTP | AutoCAD Exported Tool Palettes File | 186 |
| .XTP | xTime Project Document | 163 |
| .XTP | InfoPath Template Part File | 183 |
| .XTP | XTree Data File | 200 |
| .XTREME | Winstep Xtreme Theme Pack | 205 |
| .XUI | Xbox 360 User Interface File | 200 |
| .XUL | XML User Interface Language File | 192 |
| .XUM | Microsoft Excel Unit Operation Model | 300 |
| .XUR | Xbox 360 Binary User Interface File | 267 |
| .XV0 | Lattice XVL Structure File | 450 |
| .XV3 | Lattice XVL Geometry File | 200 |
| .XVA | XenServer Virtual Appliance File | 220 |
| .XVCT | VISE XML Project File | 300 |
| .XVD | Xbox Virtual Disk | 207 |
| .XVID | Xvid-Encoded Video File | 254 |
| .XVM | VMware Console Configuration File | 350 |
| .XVMCONF | World of Tanks XVM Configuration File | 250 |
| .XWB | XACT Wave Bank | 283 |
| .XWD | X Windows Dump Image | 314 |
| .XWF | OmniPage Workflow File | 200 |
| .XWK | Crosstalk Communicator Keyboard Mapping File | 367 |
| .XWM | Microsoft xWMA Compressed Audio | 400 |
| .XWMA | Microsoft xWMA Compressed Audio | 400 |
| .XWP | XMLwriter Project | 275 |
| .XWP | Xerox Writer Text Document | 280 |
| .XWP | Crosstalk Session File | 375 |
| .XWS | Xara Web Designer Graphic | 312 |
| .XX | XXEncoded File | 244 |
| .XXD | Brixx Planner Calendar | 289 |
| .XXE | XXEncoded File | 270 |
| .XXX | Extractor Ransomware Encrypted File | 340 |
| .XXX | Compucon Singer Embroidery File | 257 |
| .XY | XYWrite Document | 233 |
| .XY3 | XYWrite III Document | 400 |
| .XYP | XYWrite Plus Document | 367 |
| .XYS | XYplorer Script File | 300 |
| .XYW | XYWrite for Windows Document | 300 |
| .XYZ | Molecule Specification File | 327 |
| .XYZ | Celestia Sampled Trajectory Data File | 429 |
| .XYZV | Celestia Sampled Trajectory File | 275 |
| .XZ | XZ Compressed Archive | 250 |
| .XZFX | ZipLogix ZipForm File | 257 |
| .XZM | Porteus Module | 333 |
| .X_B | Parasolid Model Part File | 232 |
| .X_T | Parasolid Model Part File | 304 |