<p>I'd advise you to use the search function a bit more, as you are asking a lot of questions which have already been answered.</p>
<blockquote>
<p>When it is broadcast, other full nodes will ignore it as spam, and typically disconnect from the node that sent it. A bad block is unlikely to propagate very far on the network.</p>
<p>When other miners see it, they will also ignore it. If they mine on top of it, they will be wasting their hashing power. This also means that the miner who did the proof of work on the invalid block has wasted their own hashing power. This is why it's important that miners validate the transactions they include in blocks.</p>
</blockquote>
<p><strong><a href="https://bitcoin.stackexchange.com/questions/55316/what-happens-if-a-miner-publishes-a-block-which-contains-an-invalid-transaction">What happens if a miner publishes a block which contains an invalid transaction?</a></strong></p>

CC BY-SA 3.0
2018-03-27T12:12:41.077Z
Thanks for your answer, but in future, please vote to close the question as a duplicate rather than quoting the answer here too :)
meshcollider
CC BY-SA 3.0
2018-03-27T12:27:03.260Z
True its a duplicate and I should have linked the other question for reference. I cannot comment on that question so I'll ask it here. According to that answer, it does seem that a miner does have to somehow verify previous blocks. If this is true, how many previous blocks does he check?(should I ask this as a separate question?)
rahs
CC BY-SA 3.0
2018-03-28T08:29:00.663Z
@RahulSaha The miner indirectly checks all blocks. An interesting property of the bitcoin blockchain is that blocks which are once valid are never invalid in the future. So, you can only verify each block once and you are done.
sanket1729
CC BY-SA 3.0
2018-03-28T08:53:22.473Z
@sanket1729 So does that mean that, say, if I just start mining, then I first need to check the entire blockchain?
rahs
CC BY-SA 3.0
2018-03-28T09:11:46.713Z
@RahulSaha, yes you need to check the entire blockchain. That is the entire point of bitcoin blockchain where you trustlessly arrive at the same chain without trusting anyone about the validity of the blocks
sanket1729
CC BY-SA 3.0
2018-03-28T10:25:29.183Z
@sanket1729 and how is this verification of the blockchain done? Is every transaction compared with every other transaction?
rahs
CC BY-SA 4.0
2021-06-10T17:15:15.467Z
This is not a duplicate question. The referenced link answers the question "What happens to an invalid block?", this question basically asks "How is a block invalidated?"...
AlphaOmega
CC BY-SA 4.0
2021-06-10T21:55:31.223Z
@AlphaOmega: I added another duplicate target that is a closer fit.
Murch
CC BY-SA 3.0
2018-03-27T10:31:10.870Z
2018-03-27T10:31:10.870Z
2020-06-16T11:10:03.350Z
Jan Janssen
<p>Once a miner adds a block to the chain, does every other miner have to check that block to make sure that its transactions don't violate any rules? <p>For instance, if a miner added a block with an invalid transaction, is every other miner expected to check that block (and perhaps compare each transaction in it with every other transaction in every other block, to prevent, say, double spending)?</p>

<mining-theory><transaction-verification><block-validity>
Does every miner verify blocks that are already in the Blockchain
rahs
# Does every miner verify blocks that are already in the Blockchain

(Asked by: username_0 on 2018-03-27)

Once a miner adds a block to the chain, does every other miner have to check that block to make sure that its transactions don't violate any rules?

For instance, if a miner added a block with an invalid transaction, is every other miner expected to check that block (and perhaps compare each transaction in it with every other transaction in every other block, to prevent, say, double spending)?

**Tags:** mining-theory, transaction-verification, block-validity


---

## 1 answers

### Answer by username_1 on 2018-03-27. Score: 1

I'd advise you to use the search function a bit more, as you are asking a lot of questions which have already been answered.

> When it is broadcast, other full nodes will ignore it as spam, and typically disconnect from the node that sent it. A bad block is unlikely to propagate very far on the network.
>
> When other miners see it, they will also ignore it. If they mine on top of it, they will be wasting their hashing power. This also means that the miner who did the proof of work on the invalid block has wasted their own hashing power. This is why it's important that miners validate the transactions they include in blocks.

**[What happens if a miner publishes a block which contains an invalid transaction?](https://bitcoin.stackexchange.com/questions/55316/what-happens-if-a-miner-publishes-a-block-which-contains-an-invalid-transaction)**

> **Comments:**
> **username_2**: Thanks for your answer, but in future, please vote to close the question as a duplicate rather than quoting the answer here too :)  
> **username_0**: True its a duplicate and I should have linked the other question for reference. I cannot comment on that question so I'll ask it here. According to that answer, it does seem that a miner does have to somehow verify previous blocks. If this is true, how many previous blocks does he check?(should I ask this as a separate question?)  
> **username_3**: @RahulSaha The miner indirectly checks all blocks. An interesting property of the bitcoin blockchain is that blocks which are once valid are never invalid in the future. So, you can only verify each block once and you are done.  
> **username_0**: @username_3 So does that mean that, say, if I just start mining, then I first need to check the entire blockchain?  
> **username_3**: @RahulSaha, yes you need to check the entire blockchain. That is the entire point of bitcoin blockchain where you trustlessly arrive at the same chain without trusting anyone about the validity of the blocks  
> **username_0**: @username_3 and how is this verification of the blockchain done? Is every transaction compared with every other transaction?  
> **username_4**: This is not a duplicate question. The referenced link answers the question "What happens to an invalid block?", this question basically asks "How is a block invalidated?"...  
> **username_5**: @username_4: I added another duplicate target that is a closer fit.  

---

