There is a list here:
As of the time of this writing, they are:
List of .castle keys
This section provides a reference of all possible keys you can add to a Castle project file. The only required key is main.
- main: Relative path to a the Lua entry point file that Castle should use to load this game. For example, main.lua.
- title: The title of this game.
- description: A brief description of this game.
- owner: The Castle username of the owner of this game. Required in order to add this game to a Castle profile.
- dimensions: The desired dimensions of your game’s screen in LÖVE units. The default value is 800x450. See Game Dimensions and Scaling for much more detailed information.
- scaling: How your game should scale when changing size to fit screen space. Can be on, step or off. See Game Dimensions and Scaling for much more detailed information.
- upscaling: Same as scaling above but only configures the behavior when the available space is larger than your game’s dimensions.
- downscaling: Same as scaling above but only configures the behavior when the available space is smaller than your game’s dimensions.
- coverImage: A url or relative path to an image containing some artwork for this game. Castle will use this image when showing a preview of this game on profiles, in search results, and elsewhere.
- primaryColor: A hex string (without the
#) for a color that represents this game. For example, C0C0C0. Castle may use this when rendering previews of the game. - multiplayer: A dictionary with the following possible keys. If omitted, the default is a dictionary with a single key, enabled: false.
- enabled: A boolean. If true, indicates to Castle that this game is an online multiplayer game that uses Castle’s hosted multiplayer servers.
- serverMain: Similar to main. A relative path to an alternative entry point Lua file to be used when the game’s code is run on a multiplayer server.
- unlisted: A boolean. If true, Castle will not show this game in Search results, even if you added it to your profile. Default is false.