7 best working Minecraft 1.21 duplication glitches

Duplication glitches are some of the most powerful glitches in all of Minecraft. These bugs are able to duplicate items, either as individual drops when broken or as entire storage container inventories. While Mojang patches a huge number of bugs in each large update, there are always ones that get missed, meaning there are still a number of working duplication glitches for 1.21.

Seven of the best of these working duplication glitches are detailed below. This includes some details about the glitch and the uses the duplicated items can have for players.

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Seven of the best Minecraft 1.21 duplication glitches

1) Lag Item Duplication

Inventory duplication glitches are inarguably the best type of duplication glitch in 1.21. There are a few out there, but they all operate on the same principle—interrupt the game's ability to save the fact that the player put their items into a storage container.

If done properly, the items will end up being stored, but the game won't save the fact that the player got rid of them. This results in the items being saved within both the storage container and the player's inventories, duplicating them.

This glitch is particularly easy to pull off by using the render distance, simulation distance, and max framerate settings to force the game to run incredibly slowly. Then, put a bunch of items into a chest and use task manager to quickly force close the game. Upon relaunching and fixing the settings, the items should be in both inventories.

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2) TNT Duplication

A simple 1.21 TNT duplicator (Image via Mojang)

TNT duplicators take advantage of a strange interaction between TNT, slime blocks, and pistons to generate an unlimited amount of lit TNT from a single source block. While risky, these can be used to clear out huge areas or within other farms, such as wood or cobblestone farms.

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3) Tripwire duplication

A tripwire duplication glitch machine (Image via BrianCraft/YouTube)

Tripwire duplication glitches in Minecraft use trapdoors, pistons, and armor stands to automatically activate tripwires as a hook is placed. Since the tripwire hook is broken at the same time it's placed, the game gets confused, causing a duplicate tripwire hook to drop to the ground.

While this might seem like a strange item to duplicate, these hooks are quite useful. For instance, they can be used to make crossbows or set up a defensive perimeter around a multiplayer Minecraft base. They can also be traded to villagers as part of a larger trading system.

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4) String Duplication

A 1.21 string duplication machine (Image via BrianCraft)

String is another item that you can easily duplicate in large numbers. This is done by taking advantage of the strange properties that string has when it's placed on a block. If broken in a particular way, string can be made to drop extra when broken.

String is another incredibly useful item to have in such large amounts. It can be used to craft wool blocks, useful both for building and making the new Minecraft 1.21 paintings, as well as burned in a furnace as fuel or crafted into items like bows and fishing rods. There's a use for string in every stage of the game, meaning that this glitch is handy to use throughout a playthrough.

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5) End portal gravity duplication

This Minecraft duplication glitch takes advantage of the unique properties of the end portal found within Minecraft's strongholds. Blocks that fall through the portal in a particular way will end up duplicated on the other side. This means that you can duplicate any blocks affected by gravity with this glitch, including anvils, sand, and dragon eggs.

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6) Rail Duplication

An example rail duplication machine (Image via Mojang)

The next 1.21 duplication method to keep in mind while playing is rail duplication. This glitch utilizes a small redstone machine to push and pull rails back and forth quickly. This movement results in the game thinking the rails are both still placed and broken. This causes them to drop in item form while still remaining placed down, duplicating them.

This glitch can be used on any kind of rail. It makes minecarts much more efficient to use, as the normally prohibitive cost of railway systems is totally nullified.

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7) Carpet Duplication

An example of a Java Edition carpet duplicator (Image via Mojang)

The final working duplication glitch of 1.21 worth mentioning is carpet duplication. This glitch is similar to rail duplication and involves moving carpets back and forth quickly enough to cause them to duplicate and fly off onto the ground. This is an especially useful duplication farm for two reasons.

The first is that carpet is a nice way to spawnproof builds due to coming in all the different colors of Minecraft wool. This makes it nice to blend into any potential build. The other reason this duplication machine is useful is that carpet makes for a nice fuel source. This allows players to run furnaces and super smelters indefinitely just off of one carpet machine.