In addition to the potential of amino acid translation, the protein coding nature of COI leads to relatively stricter expectations of amplicon length. However, only half (n=54) of papers reported using length filtering, despite this being a relatively trivial procedure and with functions available in all metabarcoding software packages and as options in many more software tools. There may be some underreporting here; given the implementation of a length filtering parameter in many software tools that have a different primary purpose, authors may not have explicitly reported that length thresholds had been applied as part of a different procedure (note that we recorded when a single tool was reported to have fulfilled multiple tasks). Despite length filtering being widely available, and the relative algorithmic simplicity of implementation, there are no length filtering tools that allow for specification of thresholds outside of a simple minimum-maximum range, despite the internal barcode region of protein coding genes generally being expected to vary in length only by multiples of 3 bases. While trivial to implement this programmatically for an experienced bioinformatician, this lack of straightforward user-friendly availability presents a barrier to appropriate threshold implementation by those with less experience.