This tool allows users to design improved cell-penetrating peptides (CPPs) by generating mutant variants of an input sequence and predicting their CPP activity and subcellular localization. Paste a single peptide sequence in FASTA format below. The backend will systematically mutate the sequence, evaluate the variants using the two-stage classifier (ExtraTree for CPP/Non-CPP, CatBoost for localization), and return the top-ranked mutants alongside their predicted intracellular destination — Cytoplasm, Nucleus, Mitochondria, Endo/Lysosome, or Others. For input format details, see the Help page.