Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
What is Symbol Sudoku?
Symbol Sudoku is sudoku played with nine symbols instead of nine digits. Fill the 9×9 grid so that:
- every row holds each of the nine symbols once;
- every column does too;
- and so does every 3×3 box.
The symbols are the star ★, diamond ♦, spade ♠, heart ♥, club ♣, triangle ▲, circle ●, square ■ and note ♪, in the order of the legend above the grid and the buttons below it. Sudoku never adds or compares numbers, so nothing is lost in the swap: every technique that works on a classic board works here symbol for symbol, and Letter Sudoku, Color Sudoku, Emoji and Shape Sudoku are the same puzzle drawn in other pictures.
Each of the nine has its own colour as well as its own shape. On the light theme the star is amber, the diamond red, the spade navy, the heart pink, the club green, the triangle indigo, the circle orange, the square sky blue and the note purple; the dark theme uses lighter shades of the same nine, and pencil marks take their symbol’s colour too. The four card suits are deliberately not a deck’s red and black, so ♦ and ♥, or ♠ and ♣, never read as a matching pair. Shape alone is enough to play: if two of the colours look alike to you, nothing is lost.
How do you find where a symbol goes?
One symbol at a time. Pick a symbol, find every copy of it already on the board, and look at a box that still needs it: each copy rules out its own row and column. When only one empty square of the box is left, the symbol goes there, whatever else that square could hold on its own. That is a hidden single:
The colours make that sweep quick: select a square holding the symbol and every copy of it on the board lights up. The same sweep works along a row or a column: a symbol with one place left in a line goes there. And a square whose row, column and box already hold eight different symbols takes the ninth. Between them, those two moves finish every Easy and Medium board on this page.
What do Hard boards add?
Locked candidates. When singles run out, put the symbols each empty square can still hold in its pencil marks — the Notes button draws them small, each in its own colour — and look inside one box at a time. If a symbol’s places in the box all lie in one row or column, the box’s copy of that symbol is that line’s copy too, so it comes out of the rest of the line:
It works the other way round as well: a symbol confined to one box within a row or column comes out of the rest of that box. Hard boards are dug so that singles and locked candidates finish them.
And Expert boards?
Naked pairs. Two squares of one row, column or box that can each hold only the same two symbols will take those two between them, whichever way round, so no other square of that row, column or box can have either:
Expert boards are dug so that singles, locked candidates and naked pairs finish them, and they start with the fewest symbols.
Were the boards on this page fair?
Not for their first eleven days. From 2 April 2026 the generator took symbols out without checking anything, and 140 of 160 boards we dealt from that first version have more than one answer. From 13 April it checked every symbol it took out with a full search, and we re-counted 160 of its boards with a separate counter to confirm it: each had exactly one answer. What it never checked was how a board would be solved. Each level only had a number of symbols to leave, so the names meant less than they said. Expert was meant to leave 22 and managed it on 4 boards in 40, leaving a median of 25, much the same as Hard’s 26. And a solver that knows singles, locked candidates, pairs, triples and the X-Wing could not finish 26 of the 160 boards — 3 Medium, 12 Hard and 11 Expert — though the page promised that logic alone would always do.
The generator was rewritten in October 2026, the same fix as Letter and Color Sudoku’s, which dealt from the same code. It now takes a symbol out only while the level’s own steps still solve the board, which also proves the board has exactly one answer. Two faults in how the board was drawn went at the same time. On the dark theme the spade was the same dark navy as the squares, so it all but vanished from the grid, the buttons and the legend, and every pencil mark turned the same grey; each symbol now has a lighter shade of its own colour there. And a wrong symbol was marked only by turning red, which cannot mark a wrong diamond, red already; a wrong or clashing symbol now also gets a red dot in its corner.
How do the four levels differ?
By how many symbols are given, and by the steps a board is dug for. We dealt 40 fresh boards per level from the new generator, and 40 per level from the old one:
| Level | Given symbols | Dug for | Singles alone finish it | Old boards beyond our solver |
|---|---|---|---|---|
| Easy | 40 | singles | 40 of 40 | 0 of 40 |
| Medium | 32 | singles | 40 of 40 | 3 of 40 |
| Hard | 26 | + locked candidates | 37 of 40 | 12 of 40 |
| Expert | 22–25 | + naked pairs | 31 of 40 | 11 of 40 |
40 boards per level, fixed seed. Expert digs toward 22 symbols as far as its steps allow and keeps the fewest of up to six tries: 22 to 25, median 23. On the new boards nothing past naked pairs was ever needed: one Hard board could not be finished without locked candidates, and three Expert boards not without pairs.
At the top the new levels are easier than the old ones, and fair all the way down. Most Hard and Expert boards now fall to singles alone, and what makes them harder is having fewer symbols to start from — 26, and about 23 — against Medium’s 32. The old Hard and Expert were harder mainly because more than a quarter of their boards needed more than any level here teaches.
A symbol comes out only while the level’s steps — singles on Easy and Medium, plus locked candidates on Hard, plus naked pairs on Expert — still fill the grid, and each step only strikes symbols that cannot go where they are struck. We re-counted all 160 new boards with a separate counter written for the purpose: every one had exactly one answer, the stored one.
Which level should you play?
Start on Easy if sudoku is new to you, or on Medium if you know it with numbers. Easy gives 40 symbols and Medium 32, and both fall to singles alone. The page opens on Medium.
Scan by colour for the long sweeps across the board and by shape when you check one square. Notes pay off more here than on a number board: fill them in early, and a symbol’s candidates show across the grid in its own colour without reading each square. Hard and Expert then add the two moves above, on boards with fewer symbols to start from.
What do the buttons do?
Select a square, then a symbol; the page opens on Medium. Selecting a square highlights its row, its column and its box, and every copy of the symbol in it. A wrong symbol turns red and gets a red dot in its corner the moment it goes in, and so does one that repeats a symbol already in its row, column or box. Under the grid:
- Notes turns pencil marks on and off; they show as small symbols in their own colours. A correct symbol clears itself from the notes of its row, its column and its box; a wrong one leaves the other squares’ notes alone.
- Erase clears the selected square, and pressing the same symbol twice does the same.
- Undo takes back the last change to a square, though not the notes a correct symbol cleared elsewhere, and not the Mistakes count.
- Hint fills one square with its answer, picked at random rather than the square you could work out next.
- Solve asks first, then fills the grid and stops the timer.
- New Game deals another board at the level you are on; the level buttons deal one at theirs.
From a keyboard: 1–9 for the symbols in button order (1 star through 9 note), the arrow keys, Backspace or Delete and Ctrl+Z; shortcuts such as Ctrl+1 are left to the browser. The board is saved in this browser after every move, so it is waiting when you come back.
Where to go next
The same puzzle in other pictures: Emoji Sudoku has nine emoji where this page has glyphs, and Shape Sudoku nine plain shapes, each in its own colour.