My command:
/give @s minecraft:iron_sword[attribute_modifiers={modifiers:[type:'minecraft:generic.scale',uuid:[1,2,3,4],name:'Big!',amount:1.0,operation:'add_multiplied_base']}]
It's said on the website:
e.g. attribute_modifiers={modifiers:[type:'minecraft:generic.scale',uuid:[1,2,3,4],name:'Big!',amount:1.0,operation:'add_multiplied_base']}
The result:
[19:28:40] [Render thread/INFO]: [System] [CHAT] Should be "]"
[19:29:27] [Render thread/INFO]: [System] [CHAT] ...iers:[type:'minecraft:generic.scale',uuid:[1,2,3,4],name:'Big!',amount:1.0,operation:'add_multiplied_base']}]<--[HERE]
You should use {} inside the list. idk why but MOJANG seems to forget it.
Modified command, use this instead↓↓↓:
/give @s minecraft:iron_sword[attribute_modifiers={modifiers:[{type:'minecraft:generic.scale',uuid:[1,2,3,4],name:'Big!',amount:1.0,operation:'add_multiplied_base'}]}]