Open JJS in a custom server, then go to Build Mode / Presets / Uploads , choose New Upload , and select Map. After that, fill in the map title and description, then press Upload to publish it to the workshop.

Quick steps

  1. Join a custom server in JJS, since the workshop may not load properly in a normal private server.
  1. Open the workshop / uploads menu from build mode.
  1. Click New Upload and select Map.
  1. Add the map details, like title and description.
  1. Upload it, then check your workshop list to confirm it appears.

Important notes

  • One guide says map uploads may require the map to be loaded in the current server and may fail if the map has no extra parts.
  • Another guide mentions upload slots can be limited, with more slots available through in-game currency or Robux.
  • The exact labels in the menu can vary a little by update, but the flow is the same: open uploads, choose map, fill details, upload.

Common problems

  • If the workshop window does not show up, try joining a custom server instead of launching a private server directly from Roblox.
  • If the upload fails, make sure you selected Map and not a moveset.
  • If it still does not appear, re-open the workshop menu and check whether the item saved under your account.

Forum-style version

Join a custom server first.
Then go to Build Mode, open Uploads, hit New Upload, pick Map, and press Upload after entering the title/description.

TL;DR: In JJS, the basic path is custom server → build mode → uploads → new upload → map → fill details → upload.