swordtails are even easier to tell apart cause the males have a sabre ( the long tail) and the females dont and the females are a bit fatter.
but dont go by that alone, cause i bought 2 males and 2 females, but it turned out that one of the females was actually a late blooming male, his tail just took longer to grow, so now he has the body of a female with a tail and a gonopodium
so just look for the gonopodium