DupeMod: Bring Back the Vanilla Duplication Glitch in Forge
Speedrunners and TAS creators know the pain: the classic vanilla duplication trick, where you drop items, save, re-enter, pick them up, and force-quit, simply stops working once Forge is in the picture. The integrated server that Forge runs for singleplayer changes how the world and inventory are saved, breaking the glitch entirely. DupeMod: Bring Back the Vanilla Duplication Glitch in Forge solves this specific problem by recreating the duplication mechanic inside a modded environment.
Why the Vanilla Glitch Fails Under Forge
In unmodded Minecraft, the inventory and the world state are saved separately. This allows the classic Alt+F4 duplication method to work. Forge, however, runs a local server even for singleplayer worlds, unifying the save logic. This means the old trick produces no results. For Tool-Assisted Speedruns, which require precise tick control, Forge is a necessity, making the loss of the glitch a major hurdle. This mod is the bridge between those two worlds.
How the Mod Recreates the Duplication Mechanic
Instead of patching the game to re-enable the original bug, DupeMod simulates the process. When you select "Save and Quit to Title", the mod scans a specific area around your character. It records all dropped items and the contents of nearby chests into a file named latest_dupe.txt. Upon your next login, the mod reads this file and restores those items to their exact positions. The result is that the classic "drop, save, quit, rejoin, pick up, force quit" sequence works flawlessly under Forge.
Step-by-Step Duplication Process
- Drop the items you want to duplicate on the ground or place them in a nearby chest.
- Press Esc and select "Save and Quit to Title". The mod logs everything in the vicinity.
- Re-enter your world and pick up the items or retrieve them from the chest.
- Immediately force-close the game with Alt+F4. Your inventory is saved, but the world reverts to the state it was in when you quit.
- Launch Minecraft and load the world again. Your items are now duplicated.
Alternative Command and Hotkey Method
For those who prefer not to use Alt+F4, the developer included a built-in alternative. After picking up the items, simply type the command /dupe or press the default hotkey I. This simulates the forced shutdown: your movement stops, the inventory is saved, and the world reloads from the latest_dupe.txt file. This is particularly useful for TAS runs where manual frame-perfect timing is difficult.
Supported Duplication Scenarios
The mod handles three primary cases:
- Items thrown on the ground within a roughly 10-block radius of the player.
- Contents of standard chests within a 5-block radius.
- Contents of trapped chests within the same 5-block radius.
The latest_dupe.txt file stores coordinates, item IDs, stack sizes, damage values, enchantments, and custom names. Manual editing of this file is not advised, as formatting errors can crash the game and, in a TAS context, would be considered cheating. If something goes wrong, simply delete the file, and a new one will be generated on the next world exit.
Installation and Version Compatibility
DupeMod is built for a limited set of Minecraft versions because it is designed to work alongside Tickrate Changer, the primary tool for TAS builds. Before installing, verify that your game version is supported. The mod is strictly for singleplayer use; it will not function on multiplayer servers and attempting to use it there could be seen as cheating. To download DupeMod: Bring Back the Vanilla Duplication Glitch in Forge for Minecraft, you can use a launcher with a mod catalog that automatically matches compatible versions. This simplifies the process of finding the correct files and avoids manual version matching.
Use in Speedruns and TAS
While vanilla speedruns do not use mods, creating a high-quality TAS requires precise control. DupeMod eliminates the tedious process of manually copying playerdata files between worlds, which was previously required dozens of times per run. Combined with Tickrate Changer, you can build frame-by-frame sequences and achieve perfect duplication without losing accuracy. This has made the mod an essential tool in the Minecraft TAS community.
DupeMod: Bring Back the Vanilla Duplication Glitch in Forge is a niche but highly effective utility for assisted speedrunning and experimentation. It cleanly restores a legendary glitch without affecting multiplayer balance and provides convenient commands for automation. If you are into TAS or want to explore the inner workings of speedrun mechanics, this mod deserves a spot in your modpack. The installation is straightforward, and with the right launcher, you can have it running in minutes. How to install it is simple: drop the file into your mods folder or use a compatible launcher to do it for you.