CLS File

What are CLS files and how to open them

Are you having problems opening a CLS file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CLS files.

What is a CLS file?

A .CLS file is a Visual Basic Class Definition file.

A Visual Basic Class Definition file holds the source text of a single class module from Visual Basic 6 or VBA, containing both the class's code and metadata that tell the IDE how the class should behave. It is generated by exporting a class from the Visual Basic IDE or VBA editor. Software that reads class definitions (such as VB6, VBA, or parsers built for these environments) open these files in order to import classes into a project or analyze class structure.

Class modules define classes: objects with properties, methods, events, and often attributes that control things like visibility, instancing, and exposure to the host application. The file begins with metadata, follows with VB attributes, then the actual VB code. IDEs write these when users export class modules into text form so they can be edited outside the IDE and re-imported.

Internally the file starts with a header like "VERSION 1.0 CLASS" followed by a BEGIN/END block with properties such as MultiUse, then a series of "Attribute VB_Name", "Attribute VB_GlobalNameSpace", "Attribute VB_Creatable", "Attribute VB_PredeclaredId", "Attribute VB_Exposed". Code follows, ending with "End Class". The header signature "VERSION 1.0 CLASS" at offset 0 and the presence of those attribute lines are used to distinguish this format.

How to open CLS files

Important: Different programs may use files with the CLS file extension for different purposes, so unless you are sure which format your CLS file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different CLS openers which you will find listed below.

Last updated: August 31, 2026

Various apps that use files with this extension

These apps are known to open certain types of CLS files. Remember, different programs may use CLS files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about CLS file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.