Software packs are ZIP files that contain a PDSC file and other content. The following utilities help validating the content of a CMSIS-Pack:

Packchk validates PDSC files.
Also, schema validation is required for the PDSC file.
SVDConv validates SVD files.
ZIP Compression Tools create the actual ZIP archive of a Software Pack.
gen_pack.sh uses all the tools above to generate a CMSIS-Pack.