The damage indicator mod on a villager. As you can see it shows the effects and health.
Here we see how a player does a 4-health points damage to a Villager.
This mod shows the info about the mob you are looking at if you are in range of the mob. If you are, then information shows up on the top left corner. It shows health, mob type and the effects if the mob has any. This also works on multiplayer servers on players. This mod also shows the damage you deal on a mob or player, including if it is healed or not.