Introduction: this online tool shows codon usage frequency table for some protein expression systems, including E.coli, Yeast (Pichia pastoris or Saccharomyces cerevisiae), Insect (Spodoptera frugiperda) and Manalian (Human HEK or Cricetulus griseus CHO or Mouse NSO). For getting the codon usage table for your own sequence, please calculate the codon usage online.