I've personally settled on running diff's output into diff-highlight (supplied with Git!) and into ansi2html (one of them; there are many versions of it, and you can write one yourself in about 20 minutes, you only really need very few escape sequences handled, and then wrangle with CSS for additional 2 hours), and calling xdg-open on the temporary file. A neat pipeline, all in all.
replyYou might also like webdiff, which does something similar https://github.com/danvk/webdiff (I built this years ago and still use it every day.)
replymy favorite online diff viewer so far is https://diffs.dev/, very straightforward. Diff2html looks cool too given it can work in terminal
replyWhy not just use Araxis Merge or Beyond Compare?
replySome alternatives to paid solutions:
replyWinMerge is excellent, open source, and while Windows-only, it runs well in Wine without needing any tweaks.
Kdiff is open source, cross-platform, and while I personally don’t love it, it supports 4-pane merge, which is quite ergonomic and rare.