Reading the numbers.
Every move in a fighting game is measured in frames. One frame is the smallest unit the game can act in, and at 60 frames per second that is about 16 milliseconds. Knowing what a move does on block tells you whether you get to punish it.
Startup
How many frames pass between you pressing the button and the hitbox going live. It is written i10 for 10 frames. If a move you just blocked has 13 frames of disadvantage, you get 13 frames to press something that comes out in 13 or fewer.
On-block advantage
What the defender is left with once the move finishes against their guard. Positive means the attacker still has the initiative; negative means the defender recovers and gets to act first.
Attacker pressure continues. You must keep blocking.
You recover, but it is not fast enough to punish reliably.
Punishable. You get a real window.
Punish windows
A move blocked at -14 leaves you 13 frames. A move blocked at -19 leaves 18. That number is the punish window, and it is the whole basis of the punish finder.
The cutoff sits at -10 because the fastest normal hit in TEKKEN 8 is 10 frames. A -10 or worse disadvantage is therefore the first point where a punish actually exists, and anything faster than that is only situational — it needs a move your opponent cannot interrupt.
Not everything reaches
Startup alone is not enough — the move also has to be able to reach. Lows whiff over highs, so a low is useless against their standing attacks; you need a mid or high, or a low when they go low. The punish finder applies both rules, which is why it will sometimes tell you a move cannot answer a punishable move at all.
Answer with a mid or high. Lows whiff.
Answer with a mid or high.
Answer with a low — or a mid, but that is slower.
Worked example from Jin's movelist
His worst block frames, and what each one hands you. Try these in the punish finder against a character you do not main.
Punishing well
Rank safety first
A 25-damage punish that leaves you at -12 is a worse answer than a 15-damage move that is plus on block. The finder sorts safe, then plus, then damage.
Low beat lows
Against a jab you need a low. Against a low you can use a low or a mid, but the low is usually faster and forces a crouch block.
Punish on hit, not on whiff
Both work, but they are different tools. A punish on hit is guaranteed from a blocked move. A whiff punish is your reward for their recovery frames.
Punish every time
If you only punish big moves you will lose to pressure. Take the free damage whenever a window actually opens.