Hi all, The metadata specification shows the keyword field as a space separated list: https://packaging.python.org/specifications/core-metadata/#keywords PEP 566 backs that up, saying that the transformation to JSON should split that field on whitespace: https://www.python.org/dev/peps/pep-0566/#json-compatible-metadata However, distutils reads and writes that field as a comma separated list: https://github.com/python/cpython/blob/5383956583bb758f3828513bcdd011871f24a... https://github.com/python/cpython/blob/5383956583bb758f3828513bcdd011871f24a... And setuptools has inherited that: https://github.com/pypa/setuptools/blob/68dbb703705cdd64e25261a6fcc1c0cc96bc... https://github.com/pypa/setuptools/blob/68dbb703705cdd64e25261a6fcc1c0cc96bc... Given the dominance of distutils and setuptools, and the difficulty of changing distutils, I suspect it's easier to change the spec to adopt their de-facto standard as the official standard. But I'd like confirmation of this, as it will require some changes in Flit. The comma-separated format allows keywords containing a space - like 'orbital mechanics' in the example I was investigating (poliastro). Thanks, Thomas