Stardew Valley is a good example of why backing up a folder is safer than hunting for a single extension. A farm lives in its own directory, and the directory contains multiple related records. That makes the folder boundary the practical unit for backups. On Windows, macOS, and Linux the path is well documented and easy to copy once hidden application-data folders are visible. Before a major mod change or a manual save operation, copy the entire farm directory to a location outside the live Saves folder and give the copy a date.
For this PC reference, the documented storage is Windows: %APPDATA%StardewValleySaves | macOS: $HOME/.config/StardewValley/Saves/ | Linux / Steam Play: $XDG_CONFIG_HOME/StardewValley/Saves/ (normally ~/.config/StardewValley/Saves/). The known file or folder pattern is <FarmName>_<unique-id>
SaveGameInfo. Each farm is stored as a folder. Standard desktop saves include the main farm save and SaveGameInfo; the main data is XML text even though the primary file normally has no conventional extension.
Backup guidance: Copy the whole farm folder, not only one file. This preserves the main save, SaveGameInfo, and any paired backup files that may be useful for recovery. Steam Cloud and GOG Galaxy cloud support are documented. Cloud sync is convenient but should not replace a dated offline copy before mods, save editing, or migration. Launcher and cloud context matters because The normal desktop save folder is shared by Windows builds that use the standard StardewValley application-data path, while Microsoft Store/Xbox packaging and cloud behavior can differ. Do not assume a console or mobile save can be copied directly into the desktop folder.
Compatibility and recovery should stay conservative. Desktop saves are structured farm folders. Modded saves may depend on content or IDs provided by installed mods, so restoring the file without the same mod set can change behavior. If the expected progress is not visible, If a farm disappears from the load menu, compare the folder name, the main save filename, and SaveGameInfo. Keep the original folder intact before trying older backup copies. SaveEditor.com only labels a game-specific editor as available when a separate linked Tool has a verified operational runtime; this reference page by itself is not an editor claim.