Bitcoin Wiki - User contributions [en]

OP RETURN

2018-07-17T00:15:41Z

Apekato: Undo revision 62559 by Midnightmagic (talk)

'''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 output after an OP_RETURN. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to [[Proof of burn|burn]] bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 80 bytes [https://github.com/bitcoin/bitcoin/search?utf8=%E2%9C%93&q=MAX_OP_RETURN_RELAY], but does not provide a way for users to create OP_RETURN transactions.

== Is storing data in the blockchain acceptable? ==
Many members of the Bitcoin community believe that use of OP_RETURN is irresponsible in part because Bitcoin was intended to provide a record for financial transactions, not a record for arbitrary data. Additionally, it is trivially obvious that the demand for external, massively-replicated data store is essentially infinite. Despite this, the use of OP_RETURN continues unabated: while there is no global miner consensus to stop people from embedding arbitrary data in the blockchain if they want to, OP_RETURN is somewhat more efficient in terms of [http://i.imgur.com/VAGZWBK.png data bytes stored as a fraction of blockchain space consumed]. Compared to some other ways of storing data in the blockchain, OP_RETURN has the advantage of not creating bogus UTXO entries. [https://github.com/bitcoin/bitcoin/pull/5286 Discussion on GitHub pull request]

The creation of OP_RETURN outputs also destroys Bitcoins used in the outputs of OP_RETURN transactions, which contributes to future deflationary pressures.

From [https://bitcoin.org/en/release/v0.9.0#opreturn-and-data-in-the-block-chain Bitcoin Core release 0.9.0]:
<blockquote>
This change is not an endorsement of storing data in the blockchain. The OP_RETURN change creates a provably-prunable output, to avoid data storage schemes – some of which were already deployed – that were storing arbitrary data such as images as forever-unspendable TX outputs, bloating bitcoin's UTXO database.

Storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere.
</blockquote>

== OP_RETURN applications ==
OP_RETURN is used for writing human-language messages, digital asset proof-of-ownership, and storing data. Its use has been proposed for P2P application discovery. See the "prefixes" table below.

== 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. Note that this table is an attempt to catalog OP_RETURN prefixes that are already in use, *not* a system for reserving OP_RETURN prefixes! Protocols with no prefix do not use a prefix in OP_RETURN transactions.

{| class="wikitable"
|-
! Prefix !! Protocol
|-
| || [https://play.google.com/store/apps/details?id=a.apkt Apekato]
|-
| SPK || [http://coinspark.org/developers/ CoinSpark]
|-
| DOCPROOF || [http://www.proofofexistence.com/ Proof of Existence]
|-
| CryptoTests- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| CryptoProof- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| BS || [http://blocksignit.com/ BlockSign]
|-
| OA || [https://github.com/OpenAssets/open-assets-protocol/blob/master/specification.mediawiki Open Assets]
|-
| STAMPD## || [http://stampd.io/ stampd]
|-
| Factom!! || [http://factom.org/ Factom]
|-
| FACTOM00 || [http://factom.org/ Factom]
|-
| Fa || [http://factom.org/ Factom]
|-
| FA || [http://factom.org/ Factom]
|-
| tradle || [http://tradle.io/ Tradle]
|-
| LaPreuve || [http://www.lapreuve.net/ LaPreuve]
|-
| hex:5888 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| hex:5808 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| id || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| BITPROOF || [https://bitproof.io/ Bitproof]
|-
| S1 || [https://stampery.co/ Stampery]
|-
| S2 || [https://stampery.co/ Stampery]
|-
| S3 || [https://stampery.co/ Stampery]
|-
| S4 || [https://stampery.co/ Stampery]
|-
| S5 || [https://stampery.co/ Stampery]
|-
| ASCRIBE || [https://www.ascribe.io/ Ascribe]
|-
| ProveBit || [https://github.com/thereal1024/ProveBit ProveBit]
|-
| EW || [http://eternitywall.it/ Eternity Wall]
|-
| CC || [http://colu.co/ Colu]
|-
| omni || [http://www.omnilayer.org/ Omni Layer]
|-
| MG || [http://monegraph.com/ Monegraph]
|-
| RMBd || [https://app.remembr.io/ Remembr]
|-
| RMBe || [https://app.remembr.io/ Remembr]
|-
| ORIGMY || [http://originalmy.com/ OriginalMy]
|-
| BID || [http://bitpos.me/ Identity]
|}

== External resources on OP_RETURN ==
=== Viewing OP_RETURN ===
* [http://coinsecrets.org/ coinsecrets.org]: An OP_RETURN transaction explorer]
* [http://bitcoinstrings.com/ bitcoinstrings.com]: A site showing raw strings in Bitcoin transactions

=== Explaining OP_RETURN ===
* [https://github.com/coinspark/python-OP_RETURN python-OP_RETURN]
* [http://bitcoin.stackexchange.com/questions/29554/explanation-of-what-an-op-return-transaction-looks-like StackExchange: Explanation of what an OP_RETURN transaction looks like]
* [http://www.slideshare.net/coinspark/bitcoin-2-and-opreturns-the-blockchain-as-tcpip Metadata in the Blockchain: The OP_RETURN Explosion]
* [http://wlangiewicz.com/blog/2014/10/24/how-to-put-custom-messages-into-bitcoin-blockchain-op-return/ How to Put Custom Messages Into Bitcoin Blockchain - OP_RETURN]
{{DISPLAYTITLE:OP_RETURN}}

OP RETURN

2018-07-17T00:15:22Z

Apekato: Undo revision 62560 by Luke-jr (talk)

OP RETURN

2017-05-06T15:06:07Z

Apekato: /* OP_RETURN prefixes */

'''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 output after an OP_RETURN. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to [[Proof of burn|burn]] bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 80 bytes [https://github.com/bitcoin/bitcoin/search?utf8=%E2%9C%93&q=MAX_OP_RETURN_RELAY], but does not provide a way for users to create OP_RETURN transactions.

== Is storing data in the blockchain acceptable? ==
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 if they want to, and OP_RETURN is reasonably efficient in terms of [http://i.imgur.com/VAGZWBK.png data bytes stored as a fraction of blockchain space consumed]. Compared to some other ways of storing data in the blockchain, OP_RETURN has the advantage of not creating bogus UTXO entries. [https://github.com/bitcoin/bitcoin/pull/5286 Discussion on GitHub pull request]

From [https://bitcoin.org/en/release/v0.9.0#opreturn-and-data-in-the-block-chain Bitcoin Core release 0.9.0]:
<blockquote>
This change is not an endorsement of storing data in the blockchain. The OP_RETURN change creates a provably-prunable output, to avoid data storage schemes – some of which were already deployed – that were storing arbitrary data such as images as forever-unspendable TX outputs, bloating bitcoin's UTXO database.

Storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere.
</blockquote>

== OP_RETURN applications ==
OP_RETURN is used for writing human-language messages, digital asset proof-of-ownership, and storing data. Its use has been proposed for P2P application discovery. See the "prefixes" table below.

== 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. Note that this table is an attempt to catalog OP_RETURN prefixes that are already in use, *not* a system for reserving OP_RETURN prefixes! Protocols with no prefix do not use prefix in OP_RETURN transactions.

{| class="wikitable"
|-
! Prefix !! Protocol
|-
| || [https://play.google.com/store/apps/details?id=a.apkt Apekato]
|-
| SPK || [http://coinspark.org/developers/ CoinSpark]
|-
| DOCPROOF || [http://www.proofofexistence.com/ Proof of Existence]
|-
| CryptoTests- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| CryptoProof- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| BS || [http://blocksignit.com/ BlockSign]
|-
| OA || [https://github.com/OpenAssets/open-assets-protocol/blob/master/specification.mediawiki Open Assets]
|-
| STAMPD## || [http://stampd.io/ stampd]
|-
| Factom!! || [http://factom.org/ Factom]
|-
| FACTOM00 || [http://factom.org/ Factom]
|-
| Fa || [http://factom.org/ Factom]
|-
| FA || [http://factom.org/ Factom]
|-
| tradle || [http://tradle.io/ Tradle]
|-
| LaPreuve || [http://www.lapreuve.net/ LaPreuve]
|-
| hex:5888 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| hex:5808 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| id || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| BITPROOF || [https://bitproof.io/ Bitproof]
|-
| S1 || [https://stampery.co/ Stampery]
|-
| S2 || [https://stampery.co/ Stampery]
|-
| S3 || [https://stampery.co/ Stampery]
|-
| S4 || [https://stampery.co/ Stampery]
|-
| S5 || [https://stampery.co/ Stampery]
|-
| ASCRIBE || [https://www.ascribe.io/ Ascribe]
|-
| ProveBit || [https://github.com/thereal1024/ProveBit ProveBit]
|-
| EW || [http://eternitywall.it/ Eternity Wall]
|-
| CC || [http://colu.co/ Colu]
|-
| omni || [http://www.omnilayer.org/ Omni Layer]
|-
| MG || [http://monegraph.com/ Monegraph]
|-
| RMBd || [https://app.remembr.io/ Remembr]
|-
| RMBe || [https://app.remembr.io/ Remembr]
|-
| ORIGMY || [http://originalmy.com/ OriginalMy]
|-
| BID || [http://bitpos.me/ Identity]
|}

== External resources on OP_RETURN ==
=== Viewing OP_RETURN ===
* [http://coinsecrets.org/ coinsecrets.org]: An OP_RETURN transaction explorer]
* [http://bitcoinstrings.com/ bitcoinstrings.com]: A site showing raw strings in Bitcoin transactions

=== Explaining OP_RETURN ===
* [https://github.com/coinspark/python-OP_RETURN python-OP_RETURN]
* [http://bitcoin.stackexchange.com/questions/29554/explanation-of-what-an-op-return-transaction-looks-like StackExchange: Explanation of what an OP_RETURN transaction looks like]
* [http://www.slideshare.net/coinspark/bitcoin-2-and-opreturns-the-blockchain-as-tcpip Metadata in the Blockchain: The OP_RETURN Explosion]
* [http://wlangiewicz.com/blog/2014/10/24/how-to-put-custom-messages-into-bitcoin-blockchain-op-return/ How to Put Custom Messages Into Bitcoin Blockchain - OP_RETURN]
{{DISPLAYTITLE:OP_RETURN}}

OP RETURN

2017-05-06T14:55:15Z

Apekato:

'''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 output after an OP_RETURN. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to [[Proof of burn|burn]] bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 80 bytes [https://github.com/bitcoin/bitcoin/search?utf8=%E2%9C%93&q=MAX_OP_RETURN_RELAY], but does not provide a way for users to create OP_RETURN transactions.

== Is storing data in the blockchain acceptable? ==
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 if they want to, and OP_RETURN is reasonably efficient in terms of [http://i.imgur.com/VAGZWBK.png data bytes stored as a fraction of blockchain space consumed]. Compared to some other ways of storing data in the blockchain, OP_RETURN has the advantage of not creating bogus UTXO entries. [https://github.com/bitcoin/bitcoin/pull/5286 Discussion on GitHub pull request]

From [https://bitcoin.org/en/release/v0.9.0#opreturn-and-data-in-the-block-chain Bitcoin Core release 0.9.0]:
<blockquote>
This change is not an endorsement of storing data in the blockchain. The OP_RETURN change creates a provably-prunable output, to avoid data storage schemes – some of which were already deployed – that were storing arbitrary data such as images as forever-unspendable TX outputs, bloating bitcoin's UTXO database.

Storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere.
</blockquote>

== OP_RETURN applications ==
OP_RETURN is used for writing human-language messages, digital asset proof-of-ownership, and storing data. Its use has been proposed for P2P application discovery. See the "prefixes" table below.

== 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. Note that this table is an attempt to catalog OP_RETURN prefixes that are already in use, *not* a system for reserving OP_RETURN prefixes! Protocols with no prefix do not use prefixes in OP_RETURN transactions.

{| class="wikitable"
|-
! Prefix !! Protocol
|-
| || [https://play.google.com/store/apps/details?id=a.apkt Apekato]
|-
| SPK || [http://coinspark.org/developers/ CoinSpark]
|-
| DOCPROOF || [http://www.proofofexistence.com/ Proof of Existence]
|-
| CryptoTests- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| CryptoProof- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| BS || [http://blocksignit.com/ BlockSign]
|-
| OA || [https://github.com/OpenAssets/open-assets-protocol/blob/master/specification.mediawiki Open Assets]
|-
| STAMPD## || [http://stampd.io/ stampd]
|-
| Factom!! || [http://factom.org/ Factom]
|-
| FACTOM00 || [http://factom.org/ Factom]
|-
| Fa || [http://factom.org/ Factom]
|-
| FA || [http://factom.org/ Factom]
|-
| tradle || [http://tradle.io/ Tradle]
|-
| LaPreuve || [http://www.lapreuve.net/ LaPreuve]
|-
| hex:5888 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| hex:5808 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| id || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| BITPROOF || [https://bitproof.io/ Bitproof]
|-
| S1 || [https://stampery.co/ Stampery]
|-
| S2 || [https://stampery.co/ Stampery]
|-
| S3 || [https://stampery.co/ Stampery]
|-
| S4 || [https://stampery.co/ Stampery]
|-
| S5 || [https://stampery.co/ Stampery]
|-
| ASCRIBE || [https://www.ascribe.io/ Ascribe]
|-
| ProveBit || [https://github.com/thereal1024/ProveBit ProveBit]
|-
| EW || [http://eternitywall.it/ Eternity Wall]
|-
| CC || [http://colu.co/ Colu]
|-
| omni || [http://www.omnilayer.org/ Omni Layer]
|-
| MG || [http://monegraph.com/ Monegraph]
|-
| RMBd || [https://app.remembr.io/ Remembr]
|-
| RMBe || [https://app.remembr.io/ Remembr]
|-
| ORIGMY || [http://originalmy.com/ OriginalMy]
|-
| BID || [http://bitpos.me/ Identity]
|}

== External resources on OP_RETURN ==
=== Viewing OP_RETURN ===
* [http://coinsecrets.org/ coinsecrets.org]: An OP_RETURN transaction explorer]
* [http://bitcoinstrings.com/ bitcoinstrings.com]: A site showing raw strings in Bitcoin transactions

=== Explaining OP_RETURN ===
* [https://github.com/coinspark/python-OP_RETURN python-OP_RETURN]
* [http://bitcoin.stackexchange.com/questions/29554/explanation-of-what-an-op-return-transaction-looks-like StackExchange: Explanation of what an OP_RETURN transaction looks like]
* [http://www.slideshare.net/coinspark/bitcoin-2-and-opreturns-the-blockchain-as-tcpip Metadata in the Blockchain: The OP_RETURN Explosion]
* [http://wlangiewicz.com/blog/2014/10/24/how-to-put-custom-messages-into-bitcoin-blockchain-op-return/ How to Put Custom Messages Into Bitcoin Blockchain - OP_RETURN]
{{DISPLAYTITLE:OP_RETURN}}

OP RETURN

2017-05-06T14:33:51Z

Apekato:

'''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 output after an OP_RETURN. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to [[Proof of burn|burn]] bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 80 bytes [https://github.com/bitcoin/bitcoin/search?utf8=%E2%9C%93&q=MAX_OP_RETURN_RELAY], but does not provide a way for users to create OP_RETURN transactions.

== Is storing data in the blockchain acceptable? ==
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 if they want to, and OP_RETURN is reasonably efficient in terms of [http://i.imgur.com/VAGZWBK.png data bytes stored as a fraction of blockchain space consumed]. Compared to some other ways of storing data in the blockchain, OP_RETURN has the advantage of not creating bogus UTXO entries. [https://github.com/bitcoin/bitcoin/pull/5286 Discussion on GitHub pull request]

From [https://bitcoin.org/en/release/v0.9.0#opreturn-and-data-in-the-block-chain Bitcoin Core release 0.9.0]:
<blockquote>
This change is not an endorsement of storing data in the blockchain. The OP_RETURN change creates a provably-prunable output, to avoid data storage schemes – some of which were already deployed – that were storing arbitrary data such as images as forever-unspendable TX outputs, bloating bitcoin's UTXO database.

Storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere.
</blockquote>

== OP_RETURN applications ==
OP_RETURN is used for writing human-language messages, digital asset proof-of-ownership, and storing data. Its use has been proposed for P2P application discovery. See the "prefixes" table below.

== 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. Note that this table is an attempt to catalog OP_RETURN prefixes that are already in use, *not* a system for reserving OP_RETURN prefixes!

{| class="wikitable"
|-
! Prefix !! Protocol
|-
| || [https://play.google.com/store/apps/details?id=a.apkt Apekato]
|-
| SPK || [http://coinspark.org/developers/ CoinSpark]
|-
| DOCPROOF || [http://www.proofofexistence.com/ Proof of Existence]
|-
| CryptoTests- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| CryptoProof- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| BS || [http://blocksignit.com/ BlockSign]
|-
| OA || [https://github.com/OpenAssets/open-assets-protocol/blob/master/specification.mediawiki Open Assets]
|-
| STAMPD## || [http://stampd.io/ stampd]
|-
| Factom!! || [http://factom.org/ Factom]
|-
| FACTOM00 || [http://factom.org/ Factom]
|-
| Fa || [http://factom.org/ Factom]
|-
| FA || [http://factom.org/ Factom]
|-
| tradle || [http://tradle.io/ Tradle]
|-
| LaPreuve || [http://www.lapreuve.net/ LaPreuve]
|-
| hex:5888 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| hex:5808 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| id || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| BITPROOF || [https://bitproof.io/ Bitproof]
|-
| S1 || [https://stampery.co/ Stampery]
|-
| S2 || [https://stampery.co/ Stampery]
|-
| S3 || [https://stampery.co/ Stampery]
|-
| S4 || [https://stampery.co/ Stampery]
|-
| S5 || [https://stampery.co/ Stampery]
|-
| ASCRIBE || [https://www.ascribe.io/ Ascribe]
|-
| ProveBit || [https://github.com/thereal1024/ProveBit ProveBit]
|-
| EW || [http://eternitywall.it/ Eternity Wall]
|-
| CC || [http://colu.co/ Colu]
|-
| omni || [http://www.omnilayer.org/ Omni Layer]
|-
| MG || [http://monegraph.com/ Monegraph]
|-
| RMBd || [https://app.remembr.io/ Remembr]
|-
| RMBe || [https://app.remembr.io/ Remembr]
|-
| ORIGMY || [http://originalmy.com/ OriginalMy]
|-
| BID || [http://bitpos.me/ Identity]
|}

== External resources on OP_RETURN ==
=== Viewing OP_RETURN ===
* [http://coinsecrets.org/ coinsecrets.org]: An OP_RETURN transaction explorer]
* [http://bitcoinstrings.com/ bitcoinstrings.com]: A site showing raw strings in Bitcoin transactions

=== Explaining OP_RETURN ===
* [https://github.com/coinspark/python-OP_RETURN python-OP_RETURN]
* [http://bitcoin.stackexchange.com/questions/29554/explanation-of-what-an-op-return-transaction-looks-like StackExchange: Explanation of what an OP_RETURN transaction looks like]
* [http://www.slideshare.net/coinspark/bitcoin-2-and-opreturns-the-blockchain-as-tcpip Metadata in the Blockchain: The OP_RETURN Explosion]
* [http://wlangiewicz.com/blog/2014/10/24/how-to-put-custom-messages-into-bitcoin-blockchain-op-return/ How to Put Custom Messages Into Bitcoin Blockchain - OP_RETURN]
{{DISPLAYTITLE:OP_RETURN}}

OP RETURN

2017-05-06T14:32:11Z

Apekato:

'''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 output after an OP_RETURN. Since any outputs with OP_RETURN are provably unspendable, OP_RETURN outputs can be used to [[Proof of burn|burn]] bitcoins.

Currently, the default Bitcoin client relays OP_RETURN transactions up to 80 bytes [https://github.com/bitcoin/bitcoin/search?utf8=%E2%9C%93&q=MAX_OP_RETURN_RELAY], but does not provide a way for users to create OP_RETURN transactions.

== Is storing data in the blockchain acceptable? ==
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 if they want to, and OP_RETURN is reasonably efficient in terms of [http://i.imgur.com/VAGZWBK.png data bytes stored as a fraction of blockchain space consumed]. Compared to some other ways of storing data in the blockchain, OP_RETURN has the advantage of not creating bogus UTXO entries. [https://github.com/bitcoin/bitcoin/pull/5286 Discussion on GitHub pull request]

From [https://bitcoin.org/en/release/v0.9.0#opreturn-and-data-in-the-block-chain Bitcoin Core release 0.9.0]:
<blockquote>
This change is not an endorsement of storing data in the blockchain. The OP_RETURN change creates a provably-prunable output, to avoid data storage schemes – some of which were already deployed – that were storing arbitrary data such as images as forever-unspendable TX outputs, bloating bitcoin's UTXO database.

Storing arbitrary data in the blockchain is still a bad idea; it is less costly and far more efficient to store non-currency data elsewhere.
</blockquote>

== OP_RETURN applications ==
OP_RETURN is used for writing human-language messages, digital asset proof-of-ownership, and storing data. Its use has been proposed for P2P application discovery. See the "prefixes" table below.

== 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. Note that this table is an attempt to catalog OP_RETURN prefixes that are already in use, *not* a system for reserving OP_RETURN prefixes!

{| class="wikitable"
|-
! Prefix !! Protocol
|-
| || [https://play.google.com/store/apps/details?id=a.apkt/ Apekato]
|-
| SPK || [http://coinspark.org/developers/ CoinSpark]
|-
| DOCPROOF || [http://www.proofofexistence.com/ Proof of Existence]
|-
| CryptoTests- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| CryptoProof- || [http://crypto-copyright.com/ Crypto Copyright]
|-
| BS || [http://blocksignit.com/ BlockSign]
|-
| OA || [https://github.com/OpenAssets/open-assets-protocol/blob/master/specification.mediawiki Open Assets]
|-
| STAMPD## || [http://stampd.io/ stampd]
|-
| Factom!! || [http://factom.org/ Factom]
|-
| FACTOM00 || [http://factom.org/ Factom]
|-
| Fa || [http://factom.org/ Factom]
|-
| FA || [http://factom.org/ Factom]
|-
| tradle || [http://tradle.io/ Tradle]
|-
| LaPreuve || [http://www.lapreuve.net/ LaPreuve]
|-
| hex:5888 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| hex:5808 || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| id || [http://blog.onename.com/blockstore-bitcoin/ Blockstore]
|-
| BITPROOF || [https://bitproof.io/ Bitproof]
|-
| S1 || [https://stampery.co/ Stampery]
|-
| S2 || [https://stampery.co/ Stampery]
|-
| S3 || [https://stampery.co/ Stampery]
|-
| S4 || [https://stampery.co/ Stampery]
|-
| S5 || [https://stampery.co/ Stampery]
|-
| ASCRIBE || [https://www.ascribe.io/ Ascribe]
|-
| ProveBit || [https://github.com/thereal1024/ProveBit ProveBit]
|-
| EW || [http://eternitywall.it/ Eternity Wall]
|-
| CC || [http://colu.co/ Colu]
|-
| omni || [http://www.omnilayer.org/ Omni Layer]
|-
| MG || [http://monegraph.com/ Monegraph]
|-
| RMBd || [https://app.remembr.io/ Remembr]
|-
| RMBe || [https://app.remembr.io/ Remembr]
|-
| ORIGMY || [http://originalmy.com/ OriginalMy]
|-
| BID || [http://bitpos.me/ Identity]
|}

== External resources on OP_RETURN ==
=== Viewing OP_RETURN ===
* [http://coinsecrets.org/ coinsecrets.org]: An OP_RETURN transaction explorer]
* [http://bitcoinstrings.com/ bitcoinstrings.com]: A site showing raw strings in Bitcoin transactions

=== Explaining OP_RETURN ===
* [https://github.com/coinspark/python-OP_RETURN python-OP_RETURN]
* [http://bitcoin.stackexchange.com/questions/29554/explanation-of-what-an-op-return-transaction-looks-like StackExchange: Explanation of what an OP_RETURN transaction looks like]
* [http://www.slideshare.net/coinspark/bitcoin-2-and-opreturns-the-blockchain-as-tcpip Metadata in the Blockchain: The OP_RETURN Explosion]
* [http://wlangiewicz.com/blog/2014/10/24/how-to-put-custom-messages-into-bitcoin-blockchain-op-return/ How to Put Custom Messages Into Bitcoin Blockchain - OP_RETURN]
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