| tsn | RatLab Training SFA Network Data |
| tsq | Transact-SQL Script |
| tsql | Transact-SQL Script |
| tsx | TypeScript Source Code |
| tt | Visual Studio T4 Text Template |
| ttcn | TTCN-3 Script |
| tte | TextTransformer Interpreter |
| tti | TextTransformer Script |
| ttinclude | Visual Studio T4 Text Template Include |
| ttr | TextTransformer Productions |
| ttt | TextTransformer Tests |
| ttw | IBM Rational Tau Workspace |
| ttx | TextTransformer Tokens |
| tu | Turing Unit File |
| tui | NI LabWindows User Interface Data |
| tuneao | Aleph One Data |
| tup | Tup Data |
| tur | Turing Source Code |
| tvsconfig | RAD Studio Modeling Configuration |
| twig | Twig Template |
| txg | Toad Data Modeler Package |
| txl | TXL Source Code |
| txs | Tiny XML Server Script |
| tyb | Ty-Basic Source Code |
| tzjs | Turbulenz Java Application |
| tzo | Turbulenz Object |
| u2 | IBM Rational Tau U2 Model |
| u2d | Intel Fortran Compiler Internal Build Data |
| uber | Amazon Lumberyard Uber File |
| ubl | TI DaVinci User Boot Loader |
| uc3 | AVR32 UC3 Firmware Image |
| uca | Unicode Collation Algorithm Data |
| udd | OllyDbg Module Info |
| udn | Alpha Five User Definition Data |
| udo | RapidPLUS User Defined Object |