Sudoku Helper

What a Sudoku helper does that a solver does not

A Sudoku solver answers one question: what does the finished grid look like? A Sudoku helper answers a harder and more useful one: what is the next move, and why is it valid? This helper carries eighteen technique detectors. Each one looks for a specific, named pattern on the board in front of you, and when it finds one it tells you which cells make the argument, what the argument is, and which digit the argument kills.

That is the whole difference. A solver ends the puzzle. A helper hands you the step and lets you decide whether to take it. Every hint it gives names a real technique — naked single, pointing pair, X-Wing, W-Wing — and links to the article on this site that teaches it, so a hint you do not understand is one click from an explanation.

It also does the bookkeeping that makes advanced logic possible at all. The helper builds a complete set of pencil marks, keeps them current after every placement and every elimination, and reads patterns off them. Most stuck puzzles are not stuck because the player lacks a technique. They are stuck because one candidate is stale.

How to use the Sudoku helper

1. Enter the puzzle. Click a cell and type, or paste an 81-character string into the import box and press Import. Use 0 or . for blanks.
2. Press Next Hint once. The first press is not a hint. It checks the grid for duplicates, locks what you entered as the givens, and fills in every cell's pencil marks. The status line says so: Pencil marks filled in.
3. Press Next Hint again. Now the eighteen detectors run against the candidate map, and the status line reports which technique was found and how many others also apply.
4. Read the hint panel. It carries the technique name, a difficulty badge, a sentence of logic naming the actual cells, and a Learn more link to that technique's guide.
5. Apply it or solve it yourself. Apply Hint makes the placement or deletes the candidates. Or make the move by hand and press Next Hint again.
6. Repeat. Each applied step changes the candidate map, so the next hint is judged against the new board, not the old one.

If you are here to improve rather than to finish, put a gap between step four and step five. Read the technique name, cover the explanation, and try to reconstruct the argument yourself before you click. The helper is the same tool either way; the pause is what turns it into practice.

The hint the helper actually shows

Below is a real board from our generator — thirty givens, one solution — paused thirty hints into a solve. Eight of the eighteen techniques apply to this position at once: pointing pair, box/line reduction, naked pair, hidden triple, XY-Wing, W-Wing, simple colouring and almost locked set. The helper shows the pointing pair, because it is the easiest of the eight.

The argument is short enough to check by eye. In box 9, the digit 7 has only two cells left: the two ringed ones, R8C8 and R9C8. Box 9 has to contain a 7 somewhere, so the 7 is in one of those two cells — and both of them sit in column 8. Column 8's 7 is therefore already spoken for, wherever it lands. Every other cell in that column loses its 7, which here means exactly one candidate: the struck-through 7 at R4C8.

Nothing is placed. The hint deletes one pencil mark and stops. To a player expecting a number, that looks like the helper achieved nothing.

Why the elimination is the move that mattered

Press Apply Hint and look at the same cell again.

R4C8 was holding 3 and 7. With the 7 gone it holds a 3 and nothing else, so it is now a naked single and the next hint will place it. The visible half of the move — a digit appearing in a cell — was produced by the invisible half, and the invisible half is the part that had to be spotted.

This is why a helper that only fills cells teaches you very little. On any puzzle past Easy, most of the real work is deletion. Learn to see why a candidate cannot be true and the placements arrive on their own; learn only to hunt for naked singles and you will stall the first time a board has none.

The eighteen techniques this helper knows

These are the detectors, in the order the helper runs them. Every one of them has a guide on this site, and the hint panel links to it directly.

Read from the technique registry the page actually runs, in registry order, and the badges are the ones the hint panel displays. Three labels are looser than the logic underneath them: the panel says Pointing Pair even when the pattern is a pointing triple, the unique rectangle detector handles Type 1 only, and the almost locked set detector is ALS-XZ only. In each case the sentence in the hint panel names what was actually found.

How the helper decides which hint to show

There is no scoring and no cleverness. The helper walks the eighteen detectors from the top of that table, stops at the first one that fires, and shows it. Simple placements are tested before eliminations, short eliminations before long ones. If a naked single exists, you will never be shown a swordfish.

The order is a teaching order rather than a strict difficulty ranking, and the table shows where the two disagree: Swordfish and Jellyfish carry an Expert badge but are checked before four Advanced wings, because a fish is a mechanical shape you can scan for, while a wing needs you to trace a link. Easiest to find is not always lowest-rated.

This is also why the hint is worth trusting rather than second-guessing. The question the helper answers is not "what move exists here?" but "what is the simplest proof available right now?" The simplest proof is the one you can check, the one you will remember, and the one least likely to be wrong.

What the Available Techniques list is — and what it is not

Under the buttons there is a dropdown labelled Available Techniques. Until you have scanned it holds nothing but the prompt Press Next Hint to scan; after a scan it fills with every technique that applies to the board right now, easiest first, with a star on the one the helper chose. Picking a different entry redraws the grid with that technique's cells and swaps the explanation for its own.

It is not a practice filter. You cannot ask it for an X-Wing on a board that has no X-Wing — if X-Wing is not in the list, no X-Wing exists in that position, and the status line tells you how many techniques there were instead. That is a more honest answer than a search that quietly returns nothing, but it does mean the dropdown cannot be used to hunt for a pattern on demand.

Use it for the thing it is good at: seeing how many different valid arguments a single position supports. A board where eight techniques apply is a board where eight different people would each tell you a different next move, and all eight would be right. If you want to drill one named technique on purpose, the Sudoku trainer is built for that; the helper works from whatever puzzle you gave it.

When the helper runs out of logic

If none of the eighteen detectors fires, the helper does not stop. It solves the grid by backtracking, places the first empty cell in reading order, and labels the hint Trial & Error with a Fallback badge and no article link — the status line says plainly that no logical technique was found.

That hint teaches nothing, and it is meant to be read as a signal rather than a step: the board has moved past what this helper can explain. Over the 200 puzzles above it happened on seven of them, 3.5%. On a genuinely hard grid it will happen more often, because the techniques that crack those boards — forcing chains, ALS chains, three-dimensional Medusa — are not in the registry.

If you would rather see the answer than a guess at it, that is what the solver is for. Send the position there, check whether the puzzle is even valid, and come back.

Entering, importing and exporting a puzzle

The import box takes a string of exactly 81 digits and dots. Anything else is stripped before counting, so a grid pasted with spaces, line breaks or pipe characters imports fine — only the digits and dots are read, with 0 and . both meaning blank. Before accepting, the helper checks the grid for duplicates and names the offender: Duplicate 4 in row 6. An 80-character paste is refused rather than silently shifted.

There is also a URL import that the page never advertised. Append ?puzzle= and the 81 characters to this page's address and the grid loads on arrival — handy for bookmarking a position or sending one to somebody else.

Export writes the current board, not the original, so you can stop halfway, copy the string, and resume later or move the position to another tool. The keyboard works too: 1 to 9 place, Backspace, Delete or 0 erase, and the arrow keys move the selection. One thing to know: your entry becomes locked as the givens the moment you press Next Hint for the first time, and from then on those cells cannot be edited. Press Clear to start over.

Sudoku helper for beginners

Start on easy puzzles and let the helper explain singles until you can predict them. The two Beginner techniques are not variations of each other and the difference is worth having straight: a naked single is a cell with one candidate left, found by looking at a cell; a hidden single is a digit with one cell left in a house, found by looking at a digit. The second is harder to see and does far more work.

Do not worry about the Expert badges yet. The fact box above is the honest guide to what beginners need: singles accounted for almost ninety-nine per cent of every hint the engine gave across 200 puzzles. Getting fast and accurate at two techniques will carry you further than half-knowing eight.

Use Import freely. A puzzle from a newspaper, a book or another site can be typed in once and worked through one hint at a time, and you can re-import the original whenever a solve goes wrong. Speed is not the goal; a repeatable process is.

Sudoku helper for advanced players

For an experienced solver the helper is most useful as an audit. Work the grid yourself until you believe you have found something, then ask for a hint and compare. Did it find the same move? Did it find something much simpler that you walked past? The second case is the common one, and it is worth more than the first.

The Available Techniques list is the part to pay attention to here. When you have spent ten minutes on a board and the list comes back with a naked pair sitting in it, that is a measurable gap between the position and your reading of it. When the list comes back with nothing but an almost locked set, you know the board really is that hard.

The one thing the helper will not do is chain. Its registry stops at almost locked sets, so a board needing forcing chains or a longer colouring network will fall through to the trial-and-error fallback. Treat that fallback as the boundary of the tool rather than an answer, and take the position to a technique guide instead.

Common mistakes when using a Sudoku helper

The first is applying every hint the moment it appears. That finishes the puzzle and trains nothing, because recognition comes from predicting the move, not from watching it happen. The second is treating a hint as the only move: the status line usually reports several other techniques that also apply, and the one on screen is simply the easiest.

The third is jumping to advanced patterns too early. A board with an unresolved pointing pair does not need an X-Wing, and hunting for one wastes the time that a thirty-second candidate cleanup would have saved. The helper checks easy before hard for that reason, and so should you.

The fourth is expecting the helper to grade your puzzle. The difficulty badge on a hint describes that technique, not the board — an Expert badge on one almost-locked-set hint does not make the puzzle an expert puzzle, and a run of Beginner badges does not make it easy.

Using the helper to find where a solve went wrong

A helper is at its most useful on a grid that has already gone bad. If a puzzle has stopped making sense, import the original string, work forward hint by hint, and watch for the first placement that disagrees with what is on your paper. That cell is where the reasoning drifted, and the technique named next to it usually explains how.

If the helper refuses the import altogether and names a duplicate, the error is a typo rather than a deduction — you have two of the same digit in one house. If it accepts the grid but reaches Trial & Error almost immediately, the more likely explanation is that a wrong digit was entered as a given, because a correct puzzle of ordinary difficulty rarely exhausts eighteen techniques in a handful of steps.

Either way, this is more useful than clearing the board. It tells you which kind of mistake you make: candidate maintenance, pattern misreading, or a placement that felt right. Those need three different fixes.

Helper, solver, scanner and strategy guides

Use the helper when you want the next move explained. Use the Sudoku solver when you want the finished grid or a check that the puzzle is valid at all. Use the Sudoku scanner when the puzzle is on paper and you would rather photograph it than type eighty-one characters — it hands the grid straight to this page. Use the technique guides when a hint names something you have never met, and pencil marks when the candidate bookkeeping itself is the problem.

For puzzles to practise on, there is classic Sudoku, hard Sudoku and evil Sudoku online, or printable Sudoku if you would rather work on paper and bring the hard ones back here.

Start learning with the Sudoku helper

Enter a puzzle above, press Next Hint twice, and read the first thing it says. Then cover the explanation and try to make the same argument yourself. The aim is not to need fewer hints because you gave up asking; it is to need fewer hints because the eighteenth pointing pair looks obvious in a way the first one did not.