revamped_damage_system.sk

on join:
    set {_player} to the uuid of the player
    if {_player}'s NBT contains "Health":
        set {_health} to {_player}'s NBT value of "Health"
        if {_health} is not 20:
            set {_player}'s health to {_health}
    else:
        set {_player}'s NBT value of "Health" to 20
        set {_player}'s health to 20

on damage:
    cancel event
    set {_attacker} to attacker
    set {_victim} to victim
    set {_attackerItem} to tool of {_attacker}
    set {_damage} to 1
    if {_attackerItem}'s NBT contains "Damage":
        set {_damage} to {_attackerItem}'s NBT value of "Damage"
    set {_victimHealth} to {_victim}'s health - {_damage}
    if {_victimHealth} <= 0:
        set {_victimHealth} to 0
    {_victim}'s health is {_victimHealth}        

command /damage-read:
    trigger:
        if player's hand is set:
            set {_item} to player's tool
            set {_nbt} to nbt of {_item}
            if {_nbt}.contains("Damage"):
                send "Item Damage: %{_nbt::Damage}%"
            else:
                send "No Damage data found for this item."
        else:
            send "You are not holding anything."

command /damage-write <number>:
    trigger:
        if player's hand is set:
            set {_item} to player's tool
            set {_nbt} to nbt of {_item}
            {_nbt} set "Damage" to arg-1
            set nbt of {_item} to {_nbt}
            send "&cSet Damage of this item to %arg-1%." to player
        else:
            send "You are not holding anything."

on damage:
    cancel event

on server start:
    loop all players:
        set {_player} to loop-player's uuid
        if {_player}'s NBT contains "Health":
            set {_health} to {_player}'s NBT value of "Health"
            if {_health} is 0 or {_health} is below 0:
                send "&c&lYou died!" to loop-player
                send "&c&l%{name of player}% died to Something Scary!"
                play sound "entity.player.death" to the dead player