NPO files store information regarding data redundancy, or rather, redundancy summary data. Such data is used during scientific investigation for estimating number of sequences to achieve full coverage of metagenomic dataset.

NPO files are typically encountered in science labs. NPO filename extensions is associated with Nonpareil, a scientific software developed by Kostas Lab. NPO files store data in text format with entries delimited with tab character and organized in columns; format supports exporting to CSV.