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.
Known Stardew Valley save-file structure
The researched filename or folder pattern is <FarmName>_<unique-id>
SaveGameInfo. File-extension context: No single extension is sufficient to identify every relevant save record. The documented format notes are: 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.
Why an extension is not enough
A save filename can identify a likely container, but it does not prove the internal schema, game version, checksum rules, encryption state, or editability. 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. SaveEditor therefore separates file identification from Tool compatibility and only labels a game-specific Tool Verified when its exact profile/version evidence passes the runtime gate.
Where the format is stored
PC save locations: Windows: %APPDATA%StardewValleySaves | macOS: $HOME/.config/StardewValley/Saves/ | Linux / Steam Play: $XDG_CONFIG_HOME/StardewValley/Saves/ (normally ~/.config/StardewValley/Saves/). Storefront context: Steam, GOG Galaxy, Xbox / Microsoft Store. 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. This matters because two releases can use different containers or companion files even when the visible slot name is similar.
Back up before inspecting or editing
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. A read-only viewer is lower risk than a writer, but the live save should still be copied first. Cloud context also matters: 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. Keep the original bytes available so any experiment can be reversed without relying on a cloud service or automatic backup.
What this reference does not claim
This page does not infer an undocumented checksum algorithm, encryption key, compression layer, or cross-store conversion from the file extension. Troubleshooting evidence: 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. Those questions require a verified parser/profile or a game-specific source, not a generic format guess.
Verification context: Desktop save paths and cloud services were reviewed against current PCGamingWiki coverage. File-structure notes are limited to the standard farm-folder layout; no arbitrary XML rewrite is performed by this Game Hub.