What is a LISP file?
A .LISP file is traditionally a source code file written in the Lisp programming language. Developers use these text-based files to write and store application logic.
However, the .LISP extension has multiple possible meanings today. It is also used by the STOP/Djvu ransomware family. When this malicious software infects a system, it encrypts everyday files—such as JPG images, PDF documents, or ZIP archives—and appends the .LISP extension to the end of the original file name.
How to open LISP files?
If your file is standard code, you can read it using code editors like Visual Studio Code or Notepad++. Professional developers also use dedicated environments like LispWorks.
If your personal files were suddenly renamed by ransomware, standard software will not open them. You must use a specialized decryption tool or restore your data from an offline backup.
Best practices and troubleshooting
If you discover unexpected .LISP files on your computer, disconnect from the network immediately and run a reputable antivirus scan. Do not pay any ransom demands.
Because it can be difficult to know what your file contains, viewer.online/lisp analyzes .LISP files to identify their exact format and creator software, shows which programs can open the file, and usually previews it.
Summary
Identifying the true nature of a .LISP file is the critical first step to opening it. Because .LISP files use the known JPG format, viewer.online/lisp can safely open and display them online, eliminating compatibility problems.