Songhub can transpose an entire chord chart to a new key without you rewriting a single chord by hand.
Add a {transpose: ...} directive to the song and set it to either a target key (like D or Am) or a number of semitones (like 2 or -3) — everything from that point onward re-transposes automatically.
A number transposes relative to whatever key the song is already in at that point, so you can stack more than one {transpose: ...} directive through a song that changes key partway through.
Songhub inserts a comment showing the new key wherever a transpose happens, so the change is visible on the chart itself, not applied silently.