title_body: Providing metadata to `cardano-cli transaction build-raw`
upvoted_answer: Looks like you are using the CLI correctly, and the question was really about the NFT metadata standard. The usage of &quot;721&quot; as the top level key is to be compatible with Etherium token metadata and 3rd party sites that showcase ETH NFTs.
  Alessandro of BERRY/SpaceBudz is the one who proposed this as a CIP on the Cardano forums and it seems to have been widely adopted at this point.
  Edit: See also Is there a metadata standard for native assets (talking about fungible tokens first) in Cardano?