What is the CTL file format?
.ctl is the source file for a VB6 UserControl - a reusable ActiveX control component authored in Visual Basic 6.0, released in October 1998. Each .ctl file defines one UserControl class: its Visual Basic source code, property declarations, event handlers, and an Attribute block that records the control's name, class GUID, and version information.
The file is plain text, opening with the line VERSION 5.00, which identifies it as a VB5/VB6 format. Following the version header are Attribute declarations, then BeginProperty/EndProperty blocks for design-time property values, and finally the event procedures and subroutines written in Visual Basic syntax. Binary form-layout resources - embedded bitmaps and icon data - are stored separately in a paired .CTX file rather than within the .ctl itself.
The VB6 IDE (vb6.exe) is the intended authoring environment. .ctl files belong to a .VBP project file, which also references .frm (forms), .bas (standard modules), and .cls (class modules). Any plain text editor can open a .ctl file for reading, but only the VB6 IDE can compile and test the control.
Visual Basic 6.0 reached end-of-life in 2008, yet its runtime ships with Windows 10 and Windows 11, keeping legacy VB6 controls functional. In modern .NET development, UserControls are defined as .vb source files inside Windows Forms or WPF projects.
Security & safety
RISK: LOWCTL files are plain text source code. They cannot execute directly - a VB6 IDE must compile them. Treat like any source code: review before including in a project.
Format details
in a nutshell- dBASE IV Aldus Setup Control File - Legacy dBASE IV used .ctl for database setup/control data files; extremely rare today.
Programs that open CTL files
Windows4 apps
Microsoft Visual Basic 6.0 IDE
Paid Open VBP project file; CTL appears in Project Explorer. Or drag CTL onto an open project.
Microsoft Visual Studio (VB6 component)
Paid Visual Studio 6.0 ships VB6; later VS versions do NOT open CTL natively. Use VB6 IDE.
Notepad / any text editor
Free Open in any text editor to read VB6 source code (binary sections will appear garbled). 
Technical details
deep spec| Encoding | Plain text, ASCII (ANSI code page on legacy Windows systems) |
| First line signature | VERSION 5.00 (VB5/VB6 UserControl header) |
| Attribute block | Declares control name, class GUID, and versioning metadata |
| Property sections | BeginProperty / EndProperty blocks holding design-time property values |
| Binary resources | Stored in a paired .CTX file - not embedded in the .ctl text file |
| Typical file size | 1 KB - 500 KB |
| Authoring IDE | Visual Basic 6.0 IDE (vb6.exe) |
| Project association | Referenced by a .VBP project file alongside .frm (forms), .bas (modules), .cls (classes) |
| Runtime support | VB6 runtime included with Windows 10 and Windows 11 |
| IDE end-of-life | Visual Basic 6.0 IDE reached EOL in 2008; runtime support continues on modern Windows |
| .NET successor | VB.NET UserControl in .vb files within Windows Forms or WPF projects |
| Control output | Compiles to an ActiveX OCX component usable by VB6, VBA, and Internet Explorer |
| Released | 1998 (Visual Basic 5/6) |
| Latest version | VB6 (final release 1998); format unchanged, VB6 IDE still runs on Windows 10/11 |
CTL conversions
Community Q&A
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