This program helps to find rare codons in the coding region. Rare codons may induce problems when protein should be expressed in heterologous organism. Codon frequencies were taken from "Codon-Usage Database" that contains 392,382 CDS's from 11,713 organisms.
It is also possible to use the form for translation of nucleic acids. But more convenient is "6 Frame Translation". For manipulations with nucleic acid sequence (reverse, reverse/complement, double stranded) it is possible to use "Sequence Utilities" program.