Daily Brains · one classic newspaper Sudoku a day, Gentle on Monday to Fiendish on Sunday.
Sudoku is the classic number-placement puzzle in Daily Brains (/daily). Each day sets one 9×9 grid: fill every empty square so each row, each column and each 3×3 box holds the numbers 1 to 9 exactly once. The grid is generated from the puzzle number, so the whole world solves the same one, every grid has exactly one solution, and every grid can be finished by logic alone, without guessing. Its clues are laid out with 180-degree symmetry, the way a newspaper puzzle editor would set them.
STORY & LORE
How a grid is made
A randomised solver fills a complete, valid 9×9 grid. Clues are then pulled out in symmetric pairs (a square and its mirror through the centre), in random order, and a pair stays out only if the puzzle still has exactly one solution. On gentle days removal stops at a clue floor; on harder days the grid is carved down to a minimal set. The seed is the day's Daily.todayRng('sudoku'), so every device builds the identical grid, and the built grid is cached on the device so reloading is instant.
Graded like a person solves
Every candidate grid is solved by a human-style logic solver that always reaches for the easiest technique that makes progress, and the grid is graded by the hardest technique it needed. Tier 1 is singles (naked and hidden). Tier 2 adds pointing pairs, box-line reduction, and naked and hidden pairs. Tier 3 adds naked and hidden triples, the X-wing and the XY-wing. Tier 4 adds the XYZ-wing, the swordfish and naked and hidden quads. A grid that needs more than that (guessing or long chains) is thrown away, and the generator tries again until the grid matches its weekday exactly.
The weekly ramp
Monday is gentle but not trivial: at least 34 clues, singles only, and it needs several hidden singles rather than just filling in obvious squares. Tuesday drops to about 29 clues. Wednesday and Thursday need pairs and pointing (Thursday at least three times). Friday needs a triple, X-wing or XY-wing; Saturday needs two of them and a higher logic score. Sunday needs a tier-4 technique. The test suite rebuilds 400 days and proves each one is unique, symmetric and graded to its weekday.
HOW IT PLAYS
Playing
Tap a square, then tap a number on the pad below the grid; the pad sits under your thumb so the whole puzzle plays one-handed on a phone. Tapping the same number again clears it. The selected square's row, column and box are shaded, and every copy of its number is highlighted pink, including matching pencil notes. Each pad key shows how many of that number are still to place and fades out once all nine are in. On wide screens the pad moves beside the grid.
Notes, undo, erase
Notes mode pencils small candidates into a square instead of a number. With Tidy notes on (the default), placing a number clears it from the notes of every square in the same row, column and box. Undo steps back through every change; Erase clears a square's number, or its notes if it has none. Keyboard: arrows move, 1-9 place, Shift+number pencils a note, N toggles notes, Backspace erases, U or Ctrl+Z undoes, H takes a hint, P pauses.
Mistakes, conflicts and hints
With Flag mistakes on (the default), a number that does not match the solution turns red and adds one to the mistakes count. Turning the flag off hides mistakes entirely; turning it back on mid-puzzle reveals and counts any wrong numbers on the grid. Highlight conflicts separately shades any repeat in a row, column or box. Hint reveals one square: a wrong number first, otherwise a square you could find next with singles, nearest the one you have selected. Hinted squares are locked and marked with a pink corner.
Timer and pause
The clock runs while the grid is on screen and stops while a sheet is open or the tab is hidden. Tap the clock (or press P) to pause: the grid is hidden until you resume. Progress, notes, time, mistakes and hints are saved on every move and restored when you come back.
Scoring
A solved grid scores 600, plus a time bonus of up to 300 (full under the weekday's par, fading to nothing at three times par), plus 100 for a clean solve, minus 50 per mistake and 100 per hint, never below 100. The maximum is 1000. A clean solve (no mistakes, no hints) is a perfect day.
Sharing
The share card never shows the grid. It reads like: "Sudoku #34 · Wednesday (Steady) / Solved in 9:12, under par / Clean solve: no mistakes, no hints / 1000 pts · streak 4 / wowcool.world/daily/sudoku".
GALLERY
THE WEEK
| Day | Difficulty | Techniques needed | Clues | Par |
|---|---|---|---|---|
| Monday | Gentle | Singles, 4+ hidden singles | 34-35 | 6:00 |
| Tuesday | Easy | Singles, 8+ hidden singles | about 29 | 8:00 |
| Wednesday | Steady | Pairs and pointing | about 27 (minimal) | 11:00 |
| Thursday | Tricky | Pairs and pointing, 3+ times | about 27 (minimal) | 14:00 |
| Friday | Tough | Triple, X-wing or XY-wing | about 28 | 18:00 |
| Saturday | Devious | Two triples / X-wings / XY-wings | about 29 | 22:00 |
| Sunday | Fiendish | XYZ-wing, swordfish or quad | about 29 | 25:00 |
REWARDS
| Event | Reward |
|---|---|
| Solve the grid | 15 Tickets |
| Clean solve (no mistakes, no hints) | +25 Tickets |
| First Grid (first solve) | Bronze · 10 Tickets |
| Clean Sheet (a clean solve) | Silver · 20 Tickets |
| Beat the Clock (solve under par) | Bronze · 15 Tickets |
| In Pen (secret: Friday or harder, no notes, no hints) | Gold · 30 Tickets |
| Sunday Paper (solve a Fiendish Sunday) | Silver · 25 Tickets |
| Fiendishly Clean (clean Fiendish Sunday) | Gold · 50 Tickets |
| Every Edition (solve on all seven weekdays) | Gold · 40 Tickets |
| Three-Day Streak | Bronze · 15 Tickets |
| Full Week (7-day streak) | Gold · 40 Tickets |
| Puzzle Editor (30-day streak) | Legendary · 100 Tickets |
VERSION HISTORY
- First release: daily 9×9 Sudoku with symmetric clues, a unique solution, and human-technique grading (singles to swordfish and XYZ-wing) on a Monday-to-Sunday ramp.
- Tap-then-number pad built for one thumb, notes with auto-tidy, undo, erase, gentle hints, mistake flags, conflict highlighting, pause, sound, and per-device settings.
- Auto-save on every move, results sheet with time, mistakes, hints and score, spoiler-free share text, streaks and ten achievements.
- scripts/test-sudoku.mjs rebuilds 400 days: valid, unique (two independent solvers), symmetric, graded to the weekday, deterministic, no repeats.