Also definitely not a good idea in general, but I found https://md.new by guess and check. I can’t vouch for the site itself but it might be just the tool you’re looking for?
(I’ve prefixed all these with https:// so HN will linkify them but in your browser’s address bar you can usually omit that to make it more convenient)
If you like secretly like Google Docs but just don’t want to have to go though Drive to make a new doc: https://doc.new or https://docs.new
If you want to use GitHub Gist: https://gist.new
Similarly https://paper.new for Dropbox Paper
Also definitely not a good idea in general, but I found https://md.new by guess and check. I can’t vouch for the site itself but it might be just the tool you’re looking for?
(I’ve prefixed all these with https:// so HN will linkify them but in your browser’s address bar you can usually omit that to make it more convenient)