Hello! Is it possible to query for halo information using the API in a similar way to query for subhalo info?
If you mean to search across all halos, then no. The API is focused around the subhalo catalog, rather than the halo catalog, which is generally more useful.
If you want to search across halo properties, you can download the (entire) group catalog at the snapshot of interest (or use the Lab).
Thanks for the reply! Just to clarify, I mean if I know the halo ID, is there a way for me to query for particles belonging to that halo?
Yes, if you look at the API reference for cutout.hdf5 you can see that you can request a particle cutout for a halo, or a subhalo, optionally filtering to a subset of particle types and/or fields.