iDemux is an all-in-one command line tool that can be used for both demultiplexing and error correction of FASTQ files. It enables demultiplexing of i1 inline barcodes of Lexogen’s QuantSeq-Pool as well as demultiplexing of i7 and/or i5 indices of any other RNA-Seq library prep. iDemux can also be used for superior error correction of RNA-Seq libraries generated with Lexogen’s UDI 12 nt Unique Dual Indices. This C++ version is faster than the Python version but requires a certain proficiency in command line tool handling.