What is the git clone –filter option’s syntax?

The format for filter-spec is defined in the options section of git rev-list --help. You can also see it in the docs. Here’s what it currently says:

–filter=<filter-spec>

Only useful with one of the –objects*; omits objects (usually blobs) from the list of printed objects. The <filter-spec> may be one of the following:

The form --filter=blob:none omits all blobs.

The form --filter=blob:limit=<n>[kmg] omits blobs larger than n bytes or units. n may be zero. The suffixes k, m, and g can be used to name units in KiB, MiB, or GiB. For example, blob:limit=1k is the same as blob:limit=1024.

The form --filter=sparse:oid=<blob-ish> uses a sparse-checkout specification contained in the blob (or blob-expression) <blob-ish> to omit blobs that would not be required for a sparse checkout on the requested refs.