<p>Yes. From the <a href="http://www.wizards.com/magic/comprules/MagicCompRules_20110930.txt">comprehensive rules</a>:</p>

<blockquote>
  <p>401.3. Any player may count the number of cards remaining in any player's library at any time.</p>
</blockquote>

CC BY-SA 3.0
2014-06-30T22:04:03.890Z
Note: The rules linked to above is old, but the link names will always change.  The page to find the rules is here:  http://archive.wizards.com/Magic/TCG/Article.aspx?x=magic/rules, with the current rules located here:  http://media.wizards.com/images/magic/tcg/resources/rules/MagicCompRules_20140601.pdf
John
CC BY-SA 3.0
2011-11-06T18:29:12.693Z
Note that doing library counts excessively in organized play is grounds for a penalty in the same way that any other time-wasting behavior is. :)
Alex P
CC BY-SA 3.0
2011-11-06T23:01:39.383Z
In MTGO every player's library count is always displayed, so there's never any question, nor any need to stop and count.
JSBձոգչ
CC BY-SA 3.0
2011-11-06T18:00:17.937Z
2011-11-06T18:00:17.937Z
ire_and_curses
<p>The number of cards in players' hands is public knowledge, as is the number of exiled cards and cards in anyone's graveyard. But is the number of cards in your library public knowledge at all times as well? This could strongly affect decisions for players who frequently run mill decks.</p>

<magic-the-gathering>
Is the number of cards in my opponent's library public knowledge in Magic: The Gathering?
Gordon Gustafson
# Is the number of cards in my opponent's library public knowledge in Magic: The Gathering?

(Asked by: username_0 on 2011-11-06)

The number of cards in players' hands is public knowledge, as is the number of exiled cards and cards in anyone's graveyard. But is the number of cards in your library public knowledge at all times as well? This could strongly affect decisions for players who frequently run mill decks.

**Tags:** magic-the-gathering


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## 1 answers

### Answer by username_1 on 2011-11-06. Score: 17 | Accepted answer

Yes. From the [comprehensive rules](http://www.wizards.com/magic/comprules/MagicCompRules_20110930.txt):

> 401.3. Any player may count the number of cards remaining in any player's library at any time.

> **Comments:**
> **username_3**: Note that doing library counts excessively in organized play is grounds for a penalty in the same way that any other time-wasting behavior is. :)  
> **username_4**: In MTGO every player's library count is always displayed, so there's never any question, nor any need to stop and count.  
> **username_2**: Note: The rules linked to above is old, but the link names will always change.  The page to find the rules is here:  http://archive.wizards.com/Magic/TCG/Article.aspx?x=magic/rules, with the current rules located here:  http://media.wizards.com/images/magic/tcg/resources/rules/MagicCompRules_20140601.pdf  

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