The key point of construction in DNA-Encoded Library technology is the encoded DNA sequences (termed ‘codon’ sequence). The codon sequence records the corresponding building block's information, and with the addition of a primer can do PCR amplification. The DNA coding sequence information can then be ‘read’ by a high-throughput sequencer. Finally, the enrichment hit can be identified after the screening. HitGen can provide codon sequence design and synthesis as a one-stop service. The codon sequence is designed according to the connection mode and the dimensions of the DNA-encoded library. The principle of codon design includes considering GC content, the balance of ATCG bases, palindrome, hairpins, the number of identical consecutive bases and repeat base pairs, enough pairwise distance to distinguish different codon, etc. HitGen can currently provide >50,000 qualified codon sequences.