There is nothing more to say, this is a simple mod that syncs the health of everyone.
To install just drop it into the mods folder of your server.
Every time someone is damaged, everyone is damaged the same amount. For instance if someone takes 2 damage, every pther person loses 2 hp.
The same goes for healing, if someone heals, every player heals.
Furthermore if someone joins the game, it sets their health to the health of one of the players.
The above features ensure that every player has synced health.
IMPORTANT: This is a server-side mod, no need for it to be in your client’s modpack.