PreviewCode provides at-a-glance highlighted source code previews of more than 60 programming and scripting languages, and development configuration file formats. It makes use of macOS’ QuickLook mechanism: select a file and hit the spacebar to get an immediate preview of the file’s contents. It’s a handy way to view a file without opening it in an application.

PreviewCode also generates Finder thumbnail icons for all of those file types if you prefer something other than generic icons.