<p>According to <a href="https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki" rel="noreferrer">BIP 34</a> the coinbase transaction is required to start with the block height.  The format is a single byte giving the count of bytes to follow (currently 3) and then the block height in little-endian. See <a href="https://bitcoin.stackexchange.com/questions/30764/why-block-height-is-required-in-coinbase">Why block height is required in coinbase?</a> for more on the rationale.</p>

<p>478529 decimal is 0x074d41 in hex, so this block's coinbase must begin with the bytes <code>0x03 0x41 0x4d 0x07</code>.  <code>0x41 0x4d</code> happen to be the ASCII codes for the letters <code>A M</code>.</p>

<p>Likewise, 478530 decimal is 0x074d42, so we start with <code>0x03 0x42 0x4d 0x07</code>, and <code>0x42 0x4d</code> is <code>B M</code>.</p>

CC BY-SA 3.0
2017-08-02T04:27:57.860Z
2017-08-02T04:27:57.860Z
Nate Eldredge
<p>If you look at coin.dance, it looks like the coinbase transactions text start with consecutive letters. For example, <a href="https://blockchain.info/tx/aa51c1618e787679af008f0901830b9ab87eba51df81d17919dae9b511878611" rel="noreferrer">block 478529 starts with "AM"</a> and <a href="https://blockchain.info/tx/a612d4aa7f440b354f0494c7e144a110772c46303e5522bd9a369f11240b365f" rel="noreferrer">478530 starts with "BM"</a> and <a href="https://blockchain.info/tx/3a84d59eed9d92f6d9410b8edc0e947b2a2b46dd5652dee0031dc9250afc1e9b" rel="noreferrer">478531 starts with "CM"</a> and so on. This continues with DM, EM, ... all the way to <a href="https://blockchain.info/tx/05527b538c76d81b3003e7f9d8852a8fad338ee348ef3111ec084775d68da79f" rel="noreferrer">ZM</a> despite being mined by lots of different miners.</p>

<p>This looks coordinated in some way. Why is this? Can't the coinbase text be whatever the miner wants?</p>

<coinbase-transaction><bip-34>
Why do miners seem to be using consecutive letters for the Coinbase transaction text?
Jimmy Song
# Why do miners seem to be using consecutive letters for the Coinbase transaction text?

(Asked by: username_0 on 2017-08-02)

If you look at coin.dance, it looks like the coinbase transactions text start with consecutive letters. For example, [block 478529 starts with "AM"](https://blockchain.info/tx/aa51c1618e787679af008f0901830b9ab87eba51df81d17919dae9b511878611) and [478530 starts with "BM"](https://blockchain.info/tx/a612d4aa7f440b354f0494c7e144a110772c46303e5522bd9a369f11240b365f) and [478531 starts with "CM"](https://blockchain.info/tx/3a84d59eed9d92f6d9410b8edc0e947b2a2b46dd5652dee0031dc9250afc1e9b) and so on. This continues with DM, EM, ... all the way to [ZM](https://blockchain.info/tx/05527b538c76d81b3003e7f9d8852a8fad338ee348ef3111ec084775d68da79f) despite being mined by lots of different miners.

This looks coordinated in some way. Why is this? Can't the coinbase text be whatever the miner wants?

**Tags:** coinbase-transaction, bip-34


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## 1 answers

### Answer by username_1 on 2017-08-02. Score: 14 | Accepted answer

According to [BIP 34](https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki) the coinbase transaction is required to start with the block height. The format is a single byte giving the count of bytes to follow (currently 3) and then the block height in little-endian. See [Why block height is required in coinbase?](https://bitcoin.stackexchange.com/questions/30764/why-block-height-is-required-in-coinbase) for more on the rationale.

478529 decimal is 0x074d41 in hex, so this block's coinbase must begin with the bytes `0x03 0x41 0x4d 0x07`. `0x41 0x4d` happen to be the ASCII codes for the letters `A M`.

Likewise, 478530 decimal is 0x074d42, so we start with `0x03 0x42 0x4d 0x07`, and `0x42 0x4d` is `B M`.


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