Using external tool

If you wish to temporarily try out a save, you can use the third party tool UndertaleSandbox. Please note that we are in no way related to them, or any of their actions. If you wish to learn the manual way of installing, carry on with the tutorial!

Getting Started

First, you need to find your Undertale save folder. This is usually C:/Users/username/AppData/Local/UNDERTALE, but it might be different for you, who knows. It should contain at least a file called undertale.ini and a file called file0, unless you haven't saved your game yet, or the save was deleted.


Once you have found where your existing save data is, you can load it into Flowey's Time Machine to edit it. You don't have to load an existing save though you can select a preset instead at the top, or use the default preset which is set by default.


Just edit the various fields to your liking. Some fields can be hovered over with the mouse to get some information about the field.


Once you have edited the data to your liking, you can save it using the save button. Just overwrite your existing file0 and undertale.ini.

Undoing genocide erased world / selling your soul

If you erased your world, you should see a file called system_information_962.
If you sold your soul, you should also see a file called system_information_963.
Just delete these files using your file manager. If you are using the Steam version of the game, these files might be backed up and restored by the game on startup. In that case, you should delete the Steam data for UNDERTALE in addition to the system_ files. You can do this in multiple ways:

Advanced Mode

Flowey's Time Machine has an Advanced Mode for more detailed viewing and editing of file0. The vast majority of Undertale's save file is stored as a series of 512 "flags" containing extremely varied information, from your preferred pie flavor to whether you remembered Heats Flamesman's name.

Flowey's Time Machine uses a consecutive list of these flags. Flags the game never normally accesses are grayed out, and flags the game never sets are highlighted in red. Every flag has a name and a mouseover description, often sourced from PoroCYon's data site and The Undermodding Document. Check those out for more information on most flags.

Flags can be edited and saved in much the same way as in the basic interface, using the provided dropdowns, checkboxes, and numerical fields. (1 usually represents an "active" flag, as the two are equivalent in computer terms.) Many of the most important flags to various routes are more easily editable from the basic interface. However, there are a few that may warrant special interest: