Litematica

Litematica is a mod which allows you to visually "overlay" a saved build into your game, helping you build those things without lots of "rework" from making little mistakes. Commonly used when building a large project which a player has designed in Creative mode, or a mapart generated on https://rebane2001.com/mapartcraft/ (or similar site).

Litematica is available for Minecraft 1.12.2 using LiteLoader or Forge. (The internet gives claims of it working up to at least 1.19.4, but I have not tested this myself at this time)

Please note that some options in Litematica are not allowed in MCO! Specifically downloading world chunks without admin permission, and "easyPlace" (placing blocks mid-air).