user1891: 
Possible Duplicate:
How can I read information from the blockchain? 

Can anyone tell me from where exactly sites like 

http://www.bitcoinmonitor.com/ 
http://blockchain.info/
can't post more links

take their information.
How bitcoinmonitor knows what transactions have been done right now?

user323: You can get most of the information provided by those services through the use of the Bitcoin API. You might need to do some bookkeeping (for tracking transaction details and so forth), but it shouldn't be too hard. Other information needs to be extracted using additional tools, for example some packet sniffers for discovering transaction's relaters' IPs and so forth.

user85: They monitor the public blockchain from multiple Bitcoin servers. There's a very simple rule for which chain is valid -- whatever chain has the most work is the valid one.

1891: <blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="https://bitcoin.stackexchange.com/questions/4601/how-can-i-read-information-from-the-blockchain">How can I read information from the blockchain?</a>  </p>
</blockquote>



<p>Can anyone tell me from where exactly sites like </p>

<ol>
<li><a href="http://www.bitcoinmonitor.com/" rel="nofollow noreferrer">http://www.bitcoinmonitor.com/</a> </li>
<li><a href="http://blockchain.info/" rel="nofollow noreferrer">http://blockchain.info/</a>
can't post more links</li>
</ol>

<p>take their information.
How bitcoinmonitor knows what transactions have been done right now?</p>
 323: <p>You can get most of the information provided by those services through the use of the <a href="https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list" rel="nofollow">Bitcoin API</a>. You might need to do some bookkeeping (for tracking transaction details and so forth), but it shouldn't be too hard. Other information needs to be extracted using additional tools, for example some packet sniffers for discovering transaction's relaters' IPs and so forth.</p>
 85: <p>They monitor the public blockchain from multiple Bitcoin servers. There's a very simple rule for which chain is valid -- whatever chain has the most work is the valid one.</p>
