What does candidate mode mean?

It means you are noting possibilities, not answers. A cell in candidate mode holds the digits that are still legal for it, so you can track and narrow the options as you solve, exactly like pencil marks on paper.

What is the difference between manual and auto candidates?

With manual candidates you add and clear every pencil mark yourself; with auto candidates the app fills them in and updates them when you place a digit. Manual trains your eye, while auto saves bookkeeping on harder puzzles.

What is Snyder notation?

A pencil-marking discipline where you mark a digit in a box only when it has exactly two possible cells. It keeps the grid sparse so hidden pairs and pointing patterns are easy to spot.

Should I use full marks or Snyder notation?

Many solvers start in Snyder notation for speed and switch to full pencil marks only when a puzzle stalls and they need the extra detail to find an elimination.

Pencil Marks, Candidate Mode and Snyder Notation

How to record candidates with pencil marks and candidate mode, plus the disciplined Snyder method that keeps your grid uncluttered.

Pencil marks are the small candidate digits you note inside an empty cell to remember which numbers can still go there. On a screen this is usually called candidate mode (or notes mode) — same idea, just typed instead of written. It turns the invisible bookkeeping of a solve into something you can see, which is essential once a puzzle moves past the easiest deductions.

There are two broad styles. Full pencil marks record every candidate in every cell; Snyder notation records far less, on purpose, to keep the grid readable. Knowing both — and when to switch — is one of the highest-value basic skills.

What is candidate mode in Sudoku?

Candidate mode is simply pencil marks done on a screen. When you switch it on, the small numbers you enter go into a cell as candidates — the digits that could still legally go there — instead of being placed as your final answer. Apps also call it notes mode or pencil-mark mode; they all mean the same thing.

The point is the same whether you use a pen or a tablet: keep a visible record of what each empty cell can still hold. Once those candidates are on the grid, patterns like naked singles, naked pairs and hidden pairs become much easier to see, and every advanced technique builds on them.

Candidate mode = notes mode = pencil marks, just typed in.
Marks are possibilities, not your final answer for the cell.
It is the foundation every solving technique relies on.

Full pencil marks

In the full method you write, in each empty cell, every digit that is still legal there. The grid fills with small numbers, but the payoff is that naked singles, naked pairs and many other patterns become visually obvious. Keep the marks small and in a consistent corner layout so a cell with one mark stands out.

Write every legal digit in each empty cell.
A cell showing one mark is a naked single — place it.
When you place a digit, erase it from the peers' marks.

Snyder notation

Snyder notation, popularised by world champion Thomas Snyder, is a disciplined alternative that records far fewer marks. You go box by box and digit by digit, and you pencil a digit only when it has exactly two possible cells in that box. Digits with three or more options are left unmarked for now.

The result is a sparse grid in which hidden pairs and pointing patterns leap out almost immediately, because the only marks present are the high-signal ones. Many fast solvers start every puzzle in Snyder notation and only add full marks if they get stuck.

Mark a digit in a box only when it has exactly two candidate cells there.
Skip digits with three or more options until later.
Two matching marks expose hidden pairs and pointing pairs at a glance.

Auto candidates vs manual candidates

On paper you always write your own marks — that is manual candidate mode. Many apps add an auto candidate mode: the grid fills in every legal candidate for you and quietly updates them each time you place a digit, removing that number from the cells it can no longer go in.

Auto candidates are fast and remove a lot of book-keeping, but they hand you the full pencil-mark grid before you have done any scanning. Manual candidates are slower, yet writing each mark yourself is part of how you learn to see the board. A common middle path is to start manual to build the habit, then switch auto on for the hardest puzzles where the book-keeping outweighs the practice.

Manual — you add and clear every candidate yourself.
Auto — the app fills and updates candidates for you.
Manual trains your eye; auto saves time on hard grids.

Is auto candidate mode cheating?

No — auto candidate mode is a solving aid, not a cheat. It only shows you the candidates that the rules already allow; it never decides where a digit goes, so you still solve the puzzle yourself. Most online Sudoku apps offer it for exactly this reason.

The honest caveat is that leaning on auto candidates can slow down your own skills, because spotting and clearing candidates by hand is part of learning to read a grid. Many strong solvers treat it as a personal choice: purists keep it off to stay sharp, while casual players switch it on to skip the bookkeeping. What would count as cheating is a feature that places digits or reveals the solution for you — and that is a different tool entirely.

It only surfaces legal candidates — it never places a digit for you.
A widely offered aid, not against any rule of the puzzle.
Turning it off is a way to keep your manual skills sharp, not a rule.

Frequently asked questions

What is candidate mode in Sudoku?: Candidate mode is pencil marks done on a screen. The small numbers you enter go into a cell as candidates — the digits that could still legally go there — instead of being placed as your final answer. It is also called notes mode or pencil-mark mode.
What does candidate mode mean?: It means you are noting possibilities, not answers. A cell in candidate mode holds the digits that are still legal for it, so you can track and narrow the options as you solve, exactly like pencil marks on paper.
Is auto candidate mode cheating?: No. Auto candidate mode only fills in candidates the rules already allow and updates them as you play; it never decides where a digit goes, so you still solve the puzzle yourself. It is a common solving aid, not a cheat. Some solvers keep it off to keep their manual skills sharp, which is a personal choice rather than a rule.
What is the difference between manual and auto candidates?: With manual candidates you add and clear every pencil mark yourself; with auto candidates the app fills them in and updates them when you place a digit. Manual trains your eye, while auto saves bookkeeping on harder puzzles.
What is Snyder notation?: A pencil-marking discipline where you mark a digit in a box only when it has exactly two possible cells. It keeps the grid sparse so hidden pairs and pointing patterns are easy to spot.
Should I use full marks or Snyder notation?: Many solvers start in Snyder notation for speed and switch to full pencil marks only when a puzzle stalls and they need the extra detail to find an elimination.