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04_2_Creating_a_Raw_Transaction.md
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# 4.2 Creating a Raw Transaction
> **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
> :information_source: **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
You're now ready to create Bitcoin raw transactions. This allows you to send money but to craft the transactions as precisely as you want. This first section focuses on a simple one-input, one-output transaction. This sort of transaction _isn't_ actually that useful, because you're rarely going to want to send all of your money to one person (unless you're actually just forwarding it on, such as if you're moving things from one wallet to another). Thus, we don't label this section as a way to send money. It's just a foundational stepping stone to _actually_ sending money with a raw transaction.
@ -77,7 +77,7 @@ $ utxo_txid="ee9805676271f6244eba94c3d1a48b303a8f8359bf711c630eb6f2ea339d0e72"
$ utxo_vout="0"
```
> **TESTNET vs MAINNET:** Obviously the "validated-the-most" criteria would matter a lot more on mainnet, where real money is being used.
> :link: **TESTNET vs MAINNET:** Obviously the "validated-the-most" criteria would matter a lot more on mainnet, where real money is being used.
You should similarly record your recipient address, to make sure you have it right. We're again sending some money back to the TP faucet:
```
@ -124,13 +124,13 @@ $ echo $rawtxhex
You'll note that we didn't send the whole .08 BTC to our recipient. That's because of the transaction fee, which is _implicit_ when you send a raw transaction: the amount that you will pay as a fee is always equal to the amount of your input minus the amount of your output. So, you have to decrease your output a little bit from your input to make sure that your transaction goes out.
> **WARNING:** This is the very dangerous part of raw transactions!! Because you automatically expend all of the amount in the UTXOs that you use, it's critically important to make sure that you know: (1) precisely what UTXOs you're using; (2) exactly how much money they contain; (3) exactly how much money you're sending out; and (4) what the difference is. If you mess up and you use the wrong UTXO (with more money than you thought) or if you send out too little money, the excess is lost. Forever. Don't make that mistake! Know your inputs and outputs _precisely_. Or better, don't use raw transactions except as part of a carefully considered and triple-checked program.
> :warning: **WARNING:** This is the very dangerous part of raw transactions!! Because you automatically expend all of the amount in the UTXOs that you use, it's critically important to make sure that you know: (1) precisely what UTXOs you're using; (2) exactly how much money they contain; (3) exactly how much money you're sending out; and (4) what the difference is. If you mess up and you use the wrong UTXO (with more money than you thought) or if you send out too little money, the excess is lost. Forever. Don't make that mistake! Know your inputs and outputs _precisely_. Or better, don't use raw transactions except as part of a carefully considered and triple-checked program.
_How much should you spend on transaction fees?_ [Bitcoin Fees](https://bitcoinfees.21.co/) has a nice live assessment. It says that the "fastest and cheapest transaction fee is currently 220 satoshis/byte" and that "For the median transaction size of 226 bytes, this results in a fee of 49,720 satoshis".
That basic info is what we used to construct our raw transaction. We just subtracted 50,000 satoshis, which is .0005 BTC, from the amount we were sending: .0800 BTC - .0005 BC= .0795, which is what we sent. (Often transactions don't need to be the "fastest" and can get away with much lower transaction fees; we opted not to because we don't want to delay working through this tutorial.)
> **WARNING:** The lower that you set your transaction fee, the longer before your transaction is built into a block. The Bitcoin Fees sites lists expected times, from an expected 0 blocks, to 22. Since blocks are built on average every 10 minutes, that's the difference between a few minutes and a few hours! So, choose a transaction fee that's appropriate for what you're sending. Note that you should never drop below the minimum relay fee, which is .0001 BTC.
> :warning: **WARNING:** The lower that you set your transaction fee, the longer before your transaction is built into a block. The Bitcoin Fees sites lists expected times, from an expected 0 blocks, to 22. Since blocks are built on average every 10 minutes, that's the difference between a few minutes and a few hours! So, choose a transaction fee that's appropriate for what you're sending. Note that you should never drop below the minimum relay fee, which is .0001 BTC.
### Verify Your Raw Transaction