Server-side Fabric mod for Minecraft 26.2. Install SizePotion and Fabric API on the dedicated server only; players can connect with an unmodified Minecraft 26.2 client, with no client mod or resource pack. Use /getsizepotion <scale> <duration-seconds> [description words...] as a player to receive a drinkable size potion. The command requires the kaituoprops.getsizepotion permission node (Fabric identifier minecraft:kaituoprops.getsizepotion); without a permission provider, moderator level or higher can use it.
The scale must be from 0.1 through 16, excluding 1. Duration must be from 1 through 65,535 seconds. Each description word becomes a lore line, and lowercase & color and formatting codes are supported. The item is a vanilla minecraft:potion with a custom color, name, and lore. Its calculated size, reach, fall, and effect values live entirely in vanilla minecraft:custom_data; the mod registers no items, potions, effects, or data components. Existing potions remain usable through their custom data, including saved potions with the obsolete sizepotion:transformation component, which vanilla's tolerant save reader skips. See SIZE_POTION.md for the formulas and examples.
The client performs the normal drinking animation and sounds. When drinking finishes, the server reads the custom data and changes vanilla player scale, block and entity reach, fall damage multiplier, and safe fall distance. Vanilla attribute synchronization makes these changes visible to unmodified clients. It also grants Speed and Jump Boost when enlarging, or Slowness when shrinking. Normal consumption handles glass bottles and creative mode. Another size potion cannot be consumed while the transformation is active, and malformed potion data is rejected without consuming the item. The SizeChangeDuration scoreboard objective tracks remaining ticks; drinking milk or reaching zero restores the listed default attributes, removes those three effects, and grants Slow Falling I for 60 ticks.
The countdown pauses while a player is offline. Cleanup uses fixed vanilla defaults rather than saving previous attribute and effect values, so it may overwrite changes from other sources.
Build with ./gradlew build and install the resulting jar from build/libs alongside Fabric API in the dedicated server's mods directory. The build runs the unit test and dedicated-server GameTests for item serialization, existing potion saves, survival/creative consumption, interrupted drinking, rejection and inventory resynchronization, and milk cleanup. This mod is marked for the server environment and does not load in a client's singleplayer/LAN server.