Star in a Box is an interactive webapp which animates stars with different starting masses as they change during their lives. Some stars live fast-paced, dramatic lives, others change very little for billions of years. The webapp visualises the changes in mass, size, brightness and temperature for all these different stages. It allows a user to examine snapshots of a star's position on the colour-magnitude diagram (CMD) - the primary diagram used by astronomers to study evolution within stellar populations and to see how stellar parameters relate to one another.