First, let us define a “tell.”  A “tell” is a habitual action by another player that gives you a clue as to what he is holding.  In offline poker, a widening of the eyes is often a “tell” of a very strong hand.  That is one reason you see so many poker players wearing sunglasses at the table.  Its not because of the bright vegas lights.

So what might we look for in the online game that will give us clues as to when our opponents are bluffing, have the nut hand, etc?  Lets examine a few.

Speed of Play

Every online poker room has a set number of seconds that each player has to respond before he is declared either all-in or folded.  Sometimes, due to internet issues, a player's actions will almost always be slow and laggy.  However, often, the speed of play can be a good “tell.”  Typically, a quick bet is a sign of weakness, and a delayed action is a sign of strength, as the player is calculating his strategy with what he percieves to be a huge hand.  Watch how much time it takes the other players to make their action, and mentally make a note of it.  If you get a chance to see their cards at showdown, see if you can determine what they “slow bet” with and what they “fast bet” with. 

Now would be a good time to think about our own play and whether or not we exhibit these tells by our speed of play.  A good strategy is to try and take the same amount of time for every action, so that observant players cannot draw any conclusions from your own speed of play.

Use of Check Boxes/Auto Plays

If you have been to any of the online casinos, you will notice that they make use of check boxes such as “fold” “raise any”, or “call any”.  You can tell when a player has used a check box, because his action comes within the blink of an eye of the player before him.  You can use this to your advantage.  When a player has checked “raise any” it should be obvious that he has a strong hand.  If a player uses the check box to “check” then you can probably surmise that his hand is weak.  If a player uses the check box to “call any”, then maybe we can assume that he has a draw hand that he has not completed, but is definitely not ready to fold.  While these are not 100% accurate, the observant player can over time, begin to draw conclusions and make assumptions based on an opponents use of the check boxes. 

The fact that a player feels strongly enough about a hand to make a decision before even seeing the actions of the players before him, should be a “tell” as to what that player is holding.

Opponents Fold/Flop Percentage

While you cannot mark this percentage down exactly, you should over the course of several games get a sense of whether or not the player folds alot of trash hands or if he is staying in almost every pot.  This “tell” can be used both online and offline, to help you determine the strength of a players overall game.  If he folds alot of cards, beware.  If he stays in almost every pot, you can probably run over him if you play good cards.

Chat Box

Just as in brick and mortar casinos, the “chattiness” of a player can be an obvious tell.  Generally, if a player who is chatting all of a sudden gets quiet, you can bet he is playing a set of good cards.  He is spending every ounce of focus on playing his cards and squeezing out the biggest pot possible.  On the other hand, if a player is betting and becomes antagonistic in the chat box, he may be bluffing and hoping his show of “confidence” will aid him in bluffing you off the table.  Watch the chat box also for players who are “steaming” or “on tilt.”  A whining player or one who is using lots of abusive language is probably emotionally unable to play good poker until he or she calms down.

Waiting for the Big Blind

When you sit down at a Hold 'em table, many times you'll have the option of “waiting on the big blind“ to get to you, or you can post a matching big blind and start playing immediately.  This a good tell on how patient and online player will be.  If he is not patient enough to wait on the big blind to get around to him, he might not be very patient about waiting on good starting hands.  Expect him to be a loose player.  The opposite holds true for players who do wait on the big blind.  Either they are patient or cheap.  Both are pretty good qualities to have if you are playing online poker.  Cheap players, even when they are not especially skilled will tend to wait on better hands since they are loathe to throw away their bets! 

(Thanks to rpmorris1 for submitting this online tell!)

Beginner's Tells

Some of the tells that I should note here, are almost hilarious in nature, but I see it all the time in low limit poker.  The first one that comes to mind is the common “bet with a weak hand, feign weakness with a strong hand.”  If you are playing 7 stud, and a player has an Ace as a door card and pairs it on 4th street, he should bet.  If he checks, you can be sure he probably has 2 pair or 3 of a kind Aces.  He is feigning weakness.  Obvious? Definitely...but I see it all the time from beginners in online poker.

Another comical beginner tell is when a player always waits one card after he has paired before making a bet.  A player will be dealt a King on his porch in 7 stud and checks it.  The next street he is dealt a deuce and now hes betting like a madman.  Would he be betting on a pair of 2's?  Of course not, but you can be pretty sure he paired the Kings last street.

You will see many of these types of situations in your online poker career.  Make an effort to observe them in other players, while avoiding them yourself.