How the Game Knows You Did a T-Spin

Two conditions, checked when the piece locks: the last action was a rotation, and three corners are occupied.

A T-spin is not recognised by intent or by how clever the placement looked. It is a specific check the game runs when a T piece locks.

The two conditions

One: the last successful action was a rotation. If you rotated the piece and then slid it sideways, it is not a spin. The rotation must be the final thing you did.

Two: at least three of the four corners are occupied. The T piece sits in a three-by-three box; the game examines the four corner cells of that box. A cell counts as occupied if it contains a block or is outside the well. Walls and the floor count.

If both hold, it is a T-spin.

Full versus mini

There is a further distinction. Two of those corners are on the front of the T, the side the point faces.

Both front corners filled produces a full T-spin, the valuable one.
Only one front corner filled produces a mini T-spin, worth considerably

less.

There is one more rule: if the rotation required the last kick in the kick table, the most extreme offset the game will try, the spin is promoted to full regardless. That covers the T-spin triple, which is only reachable through that final kick.

Why implement it this way

Because "did the player do something clever" is not computable, and the corner test is a good proxy for it. Three occupied corners means the piece is genuinely wedged into a confined space, and requiring a rotation as the last action means sliding into an open gap does not qualify.

It is not a perfect proxy. Occasional placements score as spins without feeling like one, and a few genuinely impressive placements do not qualify. Every alternative anyone has proposed is worse.

Using the rule deliberately

Once you know the check, you can build for it. You need a gap the T fits into, three occupied corners around it, and an approach where rotation is the last move. That is the whole recipe, and every named T-spin setup is a different way of arranging it.

TETERI implements this check exactly, including the mini distinction and the final-kick promotion.

Common questions

Why did my T-spin not count?

Almost always because you slid or dropped the piece after rotating it. The rotation has to be the last successful action before the piece locks.

What is a mini T-spin?

A T-spin where only one of the two front corners of the T is occupied. It scores far less than a full T-spin: 200 points for a single rather than 800.