| xcconfig | Xcode Configuration Settings |
| xcdatamodel | Xcode Core Data Model |
| xcdatamodeld | Xcode Core Data Model |
| xcent | Xcode Entitlements Data |
| xcl | IAR System Linker Command File |
| xclangspec | Xcode Language Specification Data |
| xcmd | HyperCard External Commands |
| xcodeplugin | Xcode Plug-in |
| xcof | Mac OS Object Library |
| xcp | XLNT Script |
| xcplugin | Xcode Plug-in |
| xcplugindata | Xcode Plug-in Data |
| xcscheme | Xcode Scheme Document |
| xcsnapshots | Xcode Snapshots Data |
| xcss | RichFaces XCSS File |
| xct | XVI32 Conversion File |
| xct | Xilinx PARTGen Partlist File |
| xdf | Extensible Data Format File |
| xdf | XCAP Diff Data |
| xdf | ProWorx NXT Extended Memory Data File |
| xdfl | eXtensible Data Flow Language Document |
| xdfz | Compressed Extensible Data Format File |
| xdoclet | JBoss XDoclet Reference Data |
| xdt | Xscript Data File |
| xfdl | XPLATFORM Screen Form Definition |
| xfl | Adobe Flash Exchange Data |
| xgdw | GDevelop Extension |
| xgf | Xgridfit Program |
| xgm | Exient XGS Model Data |
| xgr | GraphEdit Filter Graph Markup Language |