downloadSpigotClassMappings

SpigotMC BuildData's per-version CLASS mappings (obf -> spigot), the axis Mojang's proguard cannot supply: spigot's class names are spigot's own invention, derivable from no Mojang artifact.

Only class mappings are published from 1.17 on — there is no -members.csrg, which is the same fact seen from the other side as "a spigot runtime's member names ARE the obf names".

The archive endpoint returns the whole file in one request; REST browse would page it as JSON lines.