delta

delta makes git diff readable: syntax-highlighted code, both files' line numbers down the middle, and the words that actually changed within a line picked out from the rest. Set it once as git's pager and every diff you ever run looks like this.

The demo opens delta's own source with an uncommitted edit in it. Run git diff, then DELTA_FEATURES=+side-by-side git diff to put the two versions in columns, git show HEAD to read a real commit, and delta /root/files/before.py /root/files/after.py to compare two files with no git involved at all. The VM is private to your browser tab; nothing you type leaves it.