Codon usage plays a crucial role when recombinant proteins are expressed in different organisms. This is especially the case if the codon usage frequency of the organism of origin and the target host organism differ significantly. Therefore, to enhance efficient gene expression it is of great importance to identify rare codons in any given DNA sequence and subsequently mutate these to codons which are more frequently used in the expression host. Rare Codon Analysis Tool is powerful for codon usage frequency of your sequence and codon usage distribution. It can help you decide if your sequence needs to be optimized for heterologous gene expression.