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