Blockers
Cards in your hand that reduce the combos your opponent can have. Holding an ace makes it half as likely that your opponent has AA.
A blocker is a card you can see that your opponent therefore can’t hold. It sounds obvious — and it’s the most concrete hand-reading tool there is, because it turns “they might have aces” into a number.
The count
AA has 6 combos. But if you hold an ace, your opponent is left with only 3 ways to make the pair: your ace blocks half of their AA. The engine counts it the same way it counts whole ranges: combos before, combos after.
That’s the hidden reason hands like A5s are the favorite bluffs for the 3-bet: the ace cuts exactly the combos (AA, AK) your opponent can continue with against the re-raise, so they fold more often than their full range suggests.
Blockers on the river
On the river, where there are no outs left, blockers are the fine-grained argument:
- For bluffing: if your hand blocks your opponent’s flushes (you hold the ace of the board’s suit), their strong hands are less likely and your bluff earns more folds.
- For calling: if you block exactly their possible bluffs, their bet is more credible than usual — a bad moment for the bluff catcher.
It’s not magic: it’s subtracting combos. The range viewer shows how many each card removes, and with that the close river decisions stop being gut calls.