TOI-663 is a cool M-dwarf (about 0.51 solar masses, 3,681 K, 0.51 solar radii), 64.2 light-years from Earth. TOI-663 b is a 4.5-Earth-mass planet, with an orbital period of 2.6 days, at 0.029 AU from its star, and an equilibrium temperature near 674 K, discovered in 2024 via transit. TOI-663 c is a 3.6-Earth-mass planet, with an orbital period of 4.7 days, at 0.044 AU from its star, and an equilibrium temperature near 553 K, discovered in 2024 via transit. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly.