For a system I need a hopper check and check which type of wool is inside the hopper so I tried this: (I execute the command in chat while I was standing on top of the hopper)

/testforblock ~ ~-1 ~ minecraft:hopper -1 {Items: 


The Block at 3 50 20 did not have the required NBT keys

So I looked on internet but it still didn't work, so can anyone tell me what I am doing wrong? I need help with the DataTag, but if anything else is wrong tell me.

Inside the hopper...

  • But you're also not an expert. I can see this because you use /testfor. ;) – Fabian Röling Apr 20 '18 at 16:08
  • /testforblock and lol i'm a command expert you should see some of my build haha you'll change your mind ;P – Khoeckman Apr 20 '18 at 16:11
  • Do you use comparators or restone dust in them? – Fabian Röling Apr 20 '18 at 16:12
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    normally not I also 've create a switch and other statements commandblocks so i actually dont use redstone i can use /blockdata – Khoeckman Apr 20 '18 at 16:13
  • You could put a link to your Minecraft forum profile or other website into your profile. That way we don't talk too much offtopic in the comments (what they are not made for). – Fabian Röling Apr 20 '18 at 16:14

That error message is really unintuitive, because what it should tell you is that the NBT has a syntax error. Items is an array tag, so you need []:

/testforblock ~ ~-1 ~ minecraft:hopper -1 {Items:[{Slot:0b,id:"minecraft:wool",Count:1b,Damage:0s}]}
  • omg yes i forgot them -_- – Khoeckman Apr 20 '18 at 16:14
  • THX lol i use them all the time, the best can make stupid mistakes ;PPP – Khoeckman Apr 20 '18 at 16:15
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    I mean, it's not really a syntax error. What he entered is perfectly valid NBT, it's just not the right NBT. – AjaxGb Apr 20 '18 at 17:25

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