www.makemkv.com

I'd like to know which of my mkv's have subtitles without manually opening each to find out.

I assume you mean that you don't PERSONALLY have to open each one...

There are tools like MediaInfo which can generate text files with information about various media files. You could also use parts of the mkvtoolnix suite to scan them.

Thanks for the reply. I ended up going with a file explorer add on - Icaros.