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A quick guide to solving Sudoku, and everything Sudoku Player UK can do.
Instructions — How to Solve a Sudoku Puzzle
The rules
A Sudoku grid is 9×9 cells, divided into nine 3×3 boxes. Some cells start filled in (the "clues") and the rest are empty. To solve the puzzle, fill every empty cell with a digit from 1-9 so that:
- Each row contains every digit 1-9 exactly once
- Each column contains every digit 1-9 exactly once
- Each 3×3 box contains every digit 1-9 exactly once
That's it — no maths or arithmetic involved, just logic. A properly set puzzle always has exactly one solution, so you never need to guess: every move can be worked out for certain.
Start with the obvious
Scan each row, column, and box for digits that are almost complete — if a row already has eight of its nine digits filled in, the last empty cell can only be the missing one. The same logic applies to boxes: if a box is missing only one or two digits, check which cells in that box could still take them, given what's already in their row and column.
Pencil marks (candidates)
Once the obvious placements are done, most puzzles need a more systematic approach: for each empty cell, work out which digits could possibly go there — i.e. which digits aren't already used in that cell's row, column, or box. These possibilities are called candidates, and jotting them down in the corner of the cell is called pencilling in. (SPUK can do this automatically — see Pencil Mode below.)
Naked singles & hidden singles
Once you have candidates marked in, two patterns solve most cells:
- Naked single — a cell has only ONE candidate left. That digit must go there.
- Hidden single — a digit appears as a candidate in only ONE cell within a row, column, or box, even if that cell also has other candidates. That digit must go there, since nowhere else in that row/column/box can take it.
Every time you place a digit, remove it as a candidate from every other cell in the same row, column, and box — that single step usually reveals several more singles, and solving becomes a chain reaction.
When you get stuck
Harder puzzles eventually run out of singles and need more advanced techniques (pairs, pointing candidates, X-Wings, and so on). Rather than searching those up separately, try Training Mode (see below) — it can explain the actual next step on the actual puzzle in front of you, not just the technique in the abstract. In the meantime, on a normal game, a hint reveals one cell's correct value so you're never stuck for good — see Hints below.
Features — What Sudoku Player UK Can Do
Starting a game
Click New Game for four ways to play:
- Pick a difficulty — Easy, Mild, Medium, or Hard — for a random puzzle, scored normally.
- Daily Challenge — see its own section below.
- Manual Entry — type in a puzzle from somewhere else (a newspaper, another site) — see below.
- Check Training Mode before picking a difficulty (or Manual Entry) to start that puzzle in Training Mode instead of normal play — see below.
Once playing: click a number on the number pad to select it (it highlights, and matching values light up on the board), then click a cell to place it — or skip the number pad entirely: click a cell, then press 1-9 on your keyboard. Your in-progress game is saved automatically, so navigating to another page and back — or closing the browser — picks up right where you left off (Manual Entry and Training Mode games are the exception; see their own sections).
Pencil mode
Toggle the ✎ button (in the header, or press P) to have SPUK automatically calculate and display every valid candidate for each empty cell. Selecting a number then highlights that digit's candidates in red across the whole board — handy for spotting hidden singles. Locked on automatically in Training Mode (see below), and unavailable during Manual Entry's typing phase (there's no puzzle to compute candidates against until you click Play).
Hints, erase, undo & stop
- Hint (?) — click it, then click an empty cell to reveal its solution. The number of hints available per game is set in Settings. Disabled for Daily Challenge, and during Manual Entry's typing phase (there's no solution to hint from until you click Play). In Training Mode, this button becomes Explain a Move instead — see below.
- Erase (✕) — click it, then click a cell you entered to clear it. Given clues can't be erased.
- Undo (↶) — reverts your last move. A small number badge on the button shows how many moves you can undo. The cell that changes briefly highlights in yellow, showing the value it had before the undo, so it's clear exactly what came back.
- Stop — clears the board and returns to the start screen. Disabled once a puzzle is complete (or if there's no active game) — nothing left to stop at that point.
Sound & haptics
A short sound (and, on supported devices, a light vibration) plays for placing/erasing a number, using a hint, undoing, and completing a puzzle. On by default — mute it for just your current session with the 🔊/🔇 icon next to the timer, or turn it off permanently in Settings. Note: haptic feedback isn't available on iOS (Apple has never supported it in Safari), only on supporting Android devices.
Daily Challenge
Everyone gets the same puzzle each day (difficulty rotates Easy → Mild → Medium → Hard day by day), ranked by solve time rather than points on its own leaderboard. Hints are disabled — it's a level playing field. Complete it once per day to build a day streak (🔥), shown alongside your rank. Starting the Daily Challenge pauses whatever regular game you had in progress; it picks back up once you return to New Game.
Manual Entry
Got a puzzle from a newspaper or another site you'd rather solve here? Type in the given numbers, and SPUK checks for duplicate entries in any row/column/box as you go, so a typo gets caught immediately rather than only surfacing once you click Play (at which point it works out the full solution, so hints become available same as any other game). Manual games are never saved or scored — there's no leaderboard entry to attribute a custom puzzle to.
Training Mode
A learning-focused way to play: no timer, never saved or scored, and pencil mode locked on throughout (seeing candidates matters more here than anywhere else). Works with a normal difficulty pick, or a Manual Entry puzzle — check the Training Mode box before starting either. Once playing, the Explain a Move button (?) finds the simplest logical step available anywhere on the board — it deliberately isn't tied to whichever cell you happen to have selected — and explains it in plain language, without ever just giving you the answer outright. Click it again (without making a move) to dig deeper: each click builds on what the previous one already found, so a chain of several small deductions can add up to something a single click wouldn't reveal on its own. Naked/Hidden Single results tell you directly what to place; anything else (a pair, pointing pair, etc.) only narrows things down rather than placing a value — for those, a small note under the explanation reminds you that clicking ? again is exactly how to keep going, so there's no need to guess when you're meant to click through further.
Currently covers Naked Singles, Hidden Singles, Naked Pairs, Hidden Pairs, Pointing Pairs, Box/Line Reduction, X-Wing, and Swordfish. Sometimes a position genuinely needs more than that, or a plain educated guess — for exactly that situation, Set Checkpoint saves your current position before you try something risky, and Restore Checkpoint jumps straight back to it in one click if the guess doesn't pan out, rather than undoing repeatedly.
Keyboard shortcuts
- 1-9 — enter that digit into the selected cell
- P — toggle pencil mode
- Arrow keys — move the selected cell
- Backspace / Delete / 0 — erase the selected cell
- H — arm the hint action (or trigger Explain a Move, in Training Mode)
- Ctrl+Z (or Cmd+Z) — undo
- Escape — clear the current selection (including any showing Training Mode explanation), or close an open modal
Timer & scoring
The timer only counts active play-time — it pauses while you're on another page or the browser's closed, so stepping away never inflates your time. Completed games score points based on difficulty (Easy 4 · Mild 6 · Medium 8 · Hard 10), minus one point per hint used. Manual Entry and Training Mode games don't run a timer or score points at all — neither is saved to the leaderboard.
Accounts & the leaderboard
You can play as a guest with no account, but guest games aren't saved or scored. Sign up to appear on the Leaderboard (filterable by today/week/month/year/all-time — Daily Challenge has its own separate, time-ranked leaderboard, shown right after you complete it), and make sure your Profile — name, country, and city — is filled in, since incomplete profiles are excluded from the leaderboard.
Settings
Signed-in players can customize their defaults from the Settings page:
- Whether pencil mode is on by default for new games
- Your default difficulty
- How many hints you get per game (0-3)
- Whether conflicting digits are highlighted live during normal play — on by default, a plain rule check (never gives away the actual solution)
- Whether a game starts automatically when you visit the site, instead of waiting for you to choose New Game, Daily Challenge, or Manual Entry
- Sound effects & haptic feedback — on by default
- Whether the Total Missing / Hints Remaining counts show in the header
- Which side(s) the number pad docks on — any combination of top, bottom, left, and right (left/right need a wide enough screen, and fall back to bottom on phones)