How to Play XXI: Rules, Scoring and Your First Grid

XXI gives you one 4×4 grid of numbers a day, the same grid as everyone else. Draw a single path through neighbouring tiles so that the numbers add up to exactly 21. You can always get there; the score is how many tiles you used to do it. Three is the obvious answer. Seven or eight is the one worth sharing.

The rules in full

There are only four, and the first two are the ones people trip on.

• Orthogonal moves only. From any tile you can go up, down, left or right. Never diagonally.
• No revisits. Each tile can appear in your path once. You cannot double back over a tile you have already used.
• Exactly 21. Your running total is shown as you drag. Stop on 21 and the path locks green. Pass 21 and it turns red — lift your finger and try again from anywhere.
• Score = tiles. A valid 21 made of 3 tiles scores 3. One made of 8 tiles scores 8. Longer is better.

That is the whole game. There is no timer, no lives and no way to lose a day. There is only the difference between the answer you found and the answer that was there.

A worked first grid

Here is the grid from the homepage demo. Numbers run 1 to 9, which is true of every XXI grid.

The quick answer jumps out if you look at the big numbers in the top-left: 9, then down to 8, then left to 4. That is 9 + 8 + 4 = 21 in three tiles, and it is the answer most people find in the first twenty seconds.

Now look at the small numbers along the bottom and up the right-hand side. Start in the bottom-right corner on the 1 and head left: 1, 2, 3. Turn up onto the other 1, right onto the 4, up through the 3 and the 5, then right onto the 2. That is 1 + 2 + 3 + 1 + 4 + 3 + 5 + 2 = 21 in eight tiles, half the board.

Same grid, same rules, same 21. The difference between the two is the entire game.

What a bust looks like

Try going from the 9 in the bottom-right up to the 6, left to the 3 and up to the 5. That reads 9, 15, 18 — then 23. The moment the total passes 21 the path turns red, and the grid is waiting for your next attempt. A bust costs you nothing except the few seconds it took, which is why it is worth being greedy and exploring long routes.

Sharing your result

When you lock in a 21, XXI gives you a result to copy: the puzzle number, your tile count, and an emoji grid showing the shape of your path. It never shows the numbers, so pasting it into a group chat is a dare rather than a spoiler. Your friends open the same grid and have to find a route at least as long as yours.

Once you have the rules down, the next thing to read is how to find the long path — there is a small set of habits that reliably turns a 4 into a 7.

Questions

Can I move diagonally in XXI?

No. A path moves to a neighbouring tile up, down, left or right only. Diagonal moves are not allowed, and neither is revisiting a tile you have already used.

What happens if I go over 21?

The path turns red and the run ends. Nothing is lost — lift your finger and start a new path from any tile. Only a path that stops on exactly 21 counts.

Is there a time limit?

No. There is no timer and no lives. The daily grid stays available all day, and the only score is the number of tiles in your best 21.