Kinapple is a database of in vitro substrates of human kinome. The substrates were experimentally identified by using in vitro kinase reaction with recombinant human protein kinases and phosphoproteomics approach (Sugiyama et.al., Sci Rep. 2019). Kinapple contains 175,574 in vitro kinase-substrate relationships and 1,427 phosphorylation motifs targeted by 289 human protein kinases.