The most complete tool for modding, decompiling and unpacking Undertale (and other GameMaker games!)
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Updated
Mar 26, 2026 - C#
Undertale is a video game by Toby Fox. Released in 2015, The game is about
the player controlling a small child who fell into a pit near mount ebott.
And separated by a magical barrier created by the humans in the past.
You have to go though a journey back to the surface while coming across
monsters. You can opt to spare monsters or kill them. There are many endings
depending on how you play the game
The most complete tool for modding, decompiling and unpacking Undertale (and other GameMaker games!)
🥧 An open source re-implementation of GameMaker: Studio's runner (YoYo Runner), targeting Undertale v1.08 (Bytecode Version 16)
Переклад Undertale українською.
A work-in-progress modding tool geared toward UNDERTALE/DELTARUNE
Independent 1:1 DELTARUNE Engine made in GameMaker Studio
👻 Simple Undertale-like game on Basys3 FPGA written in Verilog
Undertale theme for GNU GRUB.
Static site for viewing Undertale/Deltarune game scripts made so we have a site to reference when citing code on Undertale/Deltarune Wiki (original by xkeeper).
Underune maker is a map maker for Undertale and Deltarune. It contains all the assets, and you can make and customize as many rooms as you want.
Undertale AU Crossover - Jotaro Sans Simulator (Bizarre Adventure)
A WIP recreation of the Sans boss fight from Undertale for the TI-84+CE.
Save editor for Undertale Yellow.
Created by Toby Fox
Released September 2015