What is a CLS file?
A .CLS file is an extension that typically represents a "class" file. Because this is a generic term, .CLS files have multiple possible meanings. The most common use is a Visual Basic for Applications (VBA) Class Module file used by Microsoft Office to store object-oriented programming code. It is also widely used as an Apex class source code file on the Salesforce platform, and as a LaTeX document class file used by the LaTeX typesetting system.
Other uses for CLS files
Beyond source code, .CLS files are used by various specific software applications. A .CLS file can be a color set file in graphics software like PaintTool SAI or Clip Studio Paint. Some systems also disguise common file types under the .CLS extension. For example, the InterSystems Caché/IRIS platform sometimes generates .PDF files with a .CLS extension, and Google Firebase Crashlytics sometimes stores compressed crash reports as .7z archives disguised as .CLS files. It is also used as save data in the game Cities: Skylines.
How to open CLS files?
Because most .CLS files contain plain text source code (like VBA, Apex, or LaTeX), you can easily open and read them using any standard text editor, such as Notepad++ or Visual Studio Code. If you are working with an Apex file, you can manage it directly through the Salesforce developer tools. However, if your file is actually a disguised .PDF or compressed archive, opening it in a text editor will display unreadable characters. In those cases, you must rename the extension or open it with a dedicated tool like a PDF reader or 7-Zip.
Inspect and view CLS files online
Because a .CLS file can contain VBA code, LaTeX formatting, graphics settings, or even a compressed crash report, it is hard to know which software to use. You can use viewer.online/cls to analyze .CLS files to identify the exact format and creator software. It allows you to inspect the file structure, extract readable text, and check whether an online preview is available.
Summary
If you need to change your file into a standard format, we recommend file conversion to sensible target formats like .TXT, .PDF, or .ZIP on convert.guru. Ultimately, viewer.online/cls is useful for identifying, inspecting, and understanding .CLS files without installing software or dealing with compatibility problems.