| tmh | Windows Trace Message Header File |
| tmk | Turbo Pascal Tour Data |
| tml | Tapestry Markup Language Document |
| tmml | Tcl Manual Markup Language File |
| tmpl | BlueJ Template File |
| tmx | Translation Memory Exchange Document |
| tnm | Synopsys Synplify Time Names Data |
| tok | Borland C++ External Tokens File |
| tom | Tom Source Code |
| toml | TOML Source Code |
| tools | DJGPP Tools Data |
| tox | TouchDesigner Component Data |
| tp1 | SPLat Active Template |
| tph | Turbo Pascal Help |
| tpm | IBM RSA Transformation Parameters Model |
| tpu | Turbo Pascal Unit |
| tpy | TwinCAT PLC Project Variables |
| tr | TCL Trace Output |
| trb | Turbo STK Application |
| trc | True BASIC Compiled Program |
| trc | Hitachi Ladder Editor Trace File |
| trdf | Apache Jena RDF Thrift Data |
| tres | Godot Engine Text Resource Data |
| trs | WinDev HyperFileSQL Transaction Log |
| tru | True BASIC Source Code |
| trw | Turbo Debugger for Windows Session-state Settings |
| trx | WinDev HyperFileSQL Transaction TRX Log |
| ts | Turbulenz Script |
| tscn | Godot Engine Text Scene Data |
| tsf | ProWorx NXT Symbol File |
| tsn | RatLab Training SFA Network Data |
| tsq | Transact-SQL Script |
| tsql | Transact-SQL Script |
| tt | Visual Studio T4 Text Template |
| ttcn | TTCN-3 Script |