The documentation for Classic Marathon Infinity's map editor, shapes/sounds/physics editor, merge tool, and plugin XML is a work in progress. Joining the #forge channel in the Discord and reading the pins there is a good way to get started.

If you've already created a scenario, map, or plugin, continue to the next section to learn how to upload it.

To upload to the Classic Marathon Infinity workshop, you will need a folder and a preview image.

• Folder: this contains your creation. For scenarios, this will be the entire scenario install directory. For net maps, scripts, etc., it will just be a folder with a single item in it.
  
• Preview image: the store is configured to display 4:3 preview images. 640x480 works fine, but higher resolution is also OK. File sizes above 1 MB or so seem to fail, so stay below that.

Once you have prepared your creation, launch Classic Marathon Infinity. If you are subscribed to scenarios, remember that the scenario you choose is the one you will be given the option to link your creation to. So if your creation only works with Marathon Infinity, choose that as the scenario to launch.

Once you reach the menu screen, click on "Powered by Aleph One". In the about dialog box, there is a new button "Steam Workshop Uploader"


If you have not yet agreed to the Workshop terms of service, you should do that first at the link provided. Next, choose the settings for your creation:

• Upload For: this lists any previous items you have uploaded in case you want to update them. To upload a new item, leave "New Item" selected.
  
• Item Type: the type of the item being uploaded
  
• Content Type: for some items, this lets you add more tags to help organize it in Steam. Some tips:
  
  • For plugins that modify replacement textures, choose Graphics
    
  • For plugins that use a solo script to modify game behavior, choose Script
    
  • Net Only and Solo Only are primarily for Steam organization. Players can still access net maps in the solo level selector to explore them solo; and can still access solo maps in the Setup Network Game screen to gather co-op. So don't be afraid to set these appropriately
• Marathon Infinity Only: the name will change to reflect the scenario that you launched. Checking the box means that your creation relies on the scenario's shapes, sounds, etc., and that loading it in a different one would result in messed up gameplay. If your plugin is more generic, you can uncheck this to make it available to all scenarios.

Select the preview image and item directory you want to upload. You may want to enable Native File Dialogs in Preferences -> Environment before uploading; this will make it easier to find the preview image. Then click Upload.

Once uploaded, Classic Marathon Infinity will try to open the steam workshop in the overlay. On my Mac, the Steam overlay is broken right now, so if that doesn't work, you can just go to the Workshop in your browser. Once there, you can edit the title and description; upload some screenshots; and finally, set the visibility to Public so that everybody can enjoy your creation.