Microsoft are bringing the map creation tool Halo 5: Forge to (Windows 10) PC on 8 September, giving (some) PC users a free portion of Halo 5’s multiplayer to play around with. Forge apparently lets you “build, share and play new levels [and] maps” across both PC and Xbox One.
It’ll be the same Forge level-creation tool from Halo 5: Guardians, but updated with some PC-centric aspects. Mouse and keyboard controls for greater precision over object placement (and so on), as well as support for resolutions up to 4K. You’ll be able to “host and play custom matches for up to 16 players”, and search for Forge-generated stuff with a new ‘content browser’ that spans both platforms.
Halo 5: Forge is getting an update the same day it comes to PC, which includes the aforementioned browser, new ‘Mercy’ arena map and ‘Temple’ warzone map, plus “three new weapons, new Sound Dampener attachments, weapon and armor skins, and more”. All of which you can presumably use in your custom level creations.