https://github.com/koadman/graphdeconvolution/blob/32775c8141abecb32c10bc99024c8de8703199b1/external/gatb/convertToGFA.py#L74 This line introduces an optional field, using a tag which is non-compliant with respect to the GFAv1 specification. Tags are required to be a two characters long, with the pattern: `[a-zA-Z][a-zA-Z0-9]` https://github.com/GFA-spec/GFA-spec/blob/master/GFA1.md#optional-fields I would suggest `km` but it is already being used for Segment. However, there is no reason you cannot use the same tag on two different records, with different meanings. Perhaps this is confusing. Tags are also case-sensitive, so you could disambiguate it slightly with `KM`.