From Bitcoin Wiki
Revision as of 01:48, 29 December 2015 by Occupy paul st (talk | contribs) (Add Omni Layer, note Open Assets prefix)
Jump to: navigation, search

OP_RETURN is a script opcode used to mark a transaction output as invalid. Since the data after OP_RETURN are irrelevant to Bitcoin payments, arbitrary data can be added into the transaction by following the OP_RETURN with an OP_PUSHDATA. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to burn bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 40 bytes, but does not provide a way to create OP_RETURN transactions.


Some members of the Bitcoin community believe that use of OP_RETURN violates the contract of Bitcoin, because Bitcoin was intended to provide a record for financial transactions, not a record for arbitrary data. Despite this, use of OP_RETURN may continue unabated because there is no easy way to stop people from embedding arbitrary data in the blockchain, and OP_RETURN is an efficient way to do it. [bitcointalk discussion]

Resources on OP_RETURN

OP_RETURN prefixes

Often, OP_RETURN transactions include a prefix to identify which protocol they belong to. There is no standardized method of claiming OP_RETURN prefixes, and not all OP_RETURN transactions use prefixes. At the time of writing, this wiki page is probably the most complete list of OP_RETURN prefixes.

Prefix (Ascii-Encoded) Protocol/Owner Brief description
Fa Factom  ?
CC Colu  ?
OA Open Assets Issuance and transfer of user-created assets
omni Omni Layer  ?
MG Monegraph Digital work licensing
id Blockstore  ?
ASCRIBE ASCRIBE Digital work licensing
 ? Counterparty  ?