In battle, the pokemon using Softboiled will regain up to 1/2 (by integer division) of their maximum HP. If the current HP of the using pokemon is more than 1/2 of their maximum HP, then the using pokemon will be restored to their maximum HP. If the using pokemon's current HP is equal to their maximum HP, then Softboiled will fail.
Out of battle, Softboiled may be used to give HP from the using pokemon to any non-fainted pokemon in your party. The HP given by the using pokemon is 1/5th (by integer division) of their maximum HP, the receiving pokemon regains HP equivalent to the amount given.