Free Tiles Explained in Mahjong Solitaire
The most important rule in Mahjong Solitaire is also the one new players misread most often: visible does not always mean playable. A tile must be free before you can select it.
Once you understand free tiles, the board becomes easier to read. You stop hunting every visible match and start looking for the moves that create more freedom.
The two requirements
A tile is free when no tile sits on top of it and at least one of its left or right long sides is open. Both conditions matter. A tile with an open side is still blocked if another tile overlaps it from above. A tile with nothing above it is still blocked if it is squeezed between neighbors on both sides.
On this site, free tiles appear brighter and blocked tiles appear dimmer, but it is still worth learning the rule. Reading the shape yourself helps you plan several moves ahead.
Why the Turtle layout hides playable paths
The Turtle has many visible tiles along the bottom, but the central mound covers a large part of the board. A tile near the center may be visible only because you can see its face from above; it is not playable until the covering tile is gone and a side opens.
The long rows create another trap. A middle tile in a row can be completely uncovered and still blocked because it touches neighbors on both sides. Remove row-end tiles first to make the middle tiles free later.
Free does not always mean urgent
A free tile is an option, not an instruction. If a free tile is not blocking anything, you may want to leave it alone. It can serve as a future partner after you uncover a buried copy.
The best free tiles to remove are blockers: top-layer tiles, row ends, tower corners, and tiles sitting above larger groups. These moves increase the number of future free tiles.
Practice example
Suppose two matching dragons are free. One is on the top of the Turtle mound and one is on the right edge of the base. A third copy is visible but trapped between neighbors. Removing the top-and-edge pair is usually strong because it opens the mound and starts the edge row. Matching two harmless edge copies would leave the blocker in place.