Is the Sudoku solver free?

Yes. The AI hint engine and the puzzle solver are built into the free Sudoku game and need no account, no download and no API key. Everything runs in your own browser, so there is nothing to install and no usage limit.

Does the hint just reveal a digit, or explain it?

It explains it. The AI Hint engine reads your board live, computes the candidate digits for every empty cell, applies logical eliminations (naked pairs, pointing pairs), and then finds the next forced move — telling you which cell and why, so you learn the technique rather than just copying a number.

Can I paste in my own Sudoku puzzle to solve?

The solver works on the puzzles you play in the game, not on an imported grid — press Hint at any point and it solves the next step of the board in front of you. Every generated puzzle is guaranteed to have exactly one solution, verified by the backtracking solver behind the generator.

What is Auto Candidate Mode?

It fills in the small pencil-mark candidates for every empty cell automatically and keeps them updated as you place digits, so you can focus on the logic instead of the bookkeeping. You can also switch to Candidate mode with the pencil (✎) button to jot marks yourself.

How does the solver actually work?

The generator and hint engine are backed by a backtracking constraint solver: it tries digits, propagates the row, column and box constraints, and backtracks when a cell has no candidate left. That guarantees each puzzle has a unique solution and lets the hint engine always find the next correct move.

Does it work on mobile?

Yes. The Sudoku game, its hint engine and Auto Candidate Mode are fully responsive and run in any modern mobile browser, so you can play and take hints on a phone or tablet as well as a desktop.

Sudoku

How to Use the Sudoku Solver and Hint Engine

LK Forge · 4 min read · Updated September 2026

The free LK Forge Sudoku game has a solver built in — not a paste-your-grid box, but an AI Hint engine that solves the next step of the puzzle you’re playing and tells you how it found it. That makes it a solver you can learn from: instead of just handing you the answer, it names the technique. This guide covers the hint engine, the candidate tools, and the solver that powers it all. Everything runs in your browser, so nothing is uploaded.

Get the next move with AI Hint

Stuck on a puzzle? Press Hint. The engine reads the board live, works out the candidate digits for every empty cell, applies logical eliminations, and points you to the next forced move — the cell that can only be one digit — along with the reason. Because it explains the step rather than just filling it, using Hint a few times is one of the fastest ways to pick up real Sudoku technique.

Let the candidates fill themselves

Auto Candidate Mode — tick it and the small pencil-mark candidates appear in every empty cell and update automatically as you place digits, so you can focus on spotting patterns instead of bookkeeping.
Pencil marks — prefer to track candidates yourself? Switch to Candidate mode with the pencil (✎) button and jot your own marks.
Difficulty — Easy needs only single-candidate scanning; Hard and Expert demand the advanced techniques (naked pairs, pointing pairs and beyond) that the hint engine can demonstrate on demand. There’s also a Daily Challenge.

The solver behind it

Both the puzzle generator and the hint engine are backed by a backtracking constraint solver: it places a digit, propagates the row, column and box constraints to shrink every other cell’s candidates, and backtracks when a cell runs out of options. That’s what guarantees every puzzle has exactly one solution, and what lets the hint engine always find a correct next move rather than a guess. The hint layer adds the human-readable techniques (single candidate, naked pair, pointing pair) on top so the “why” is as useful as the “what”.

That’s the whole toolkit — open the Sudoku board, and lean on Hint and Auto Candidate Mode whenever you’re stuck. For more of the same, the Solvers & Analyzers hub gathers every LK Forge solver and game analyzer in one place.

Open the free Sudoku game and press Hint for the next logical move, with the technique that finds it named.

Open the Sudoku Solver

Frequently asked questions

Is the Sudoku solver free?: Yes. The AI hint engine and the puzzle solver are built into the free Sudoku game and need no account, no download and no API key. Everything runs in your own browser, so there is nothing to install and no usage limit.
Does the hint just reveal a digit, or explain it?: It explains it. The AI Hint engine reads your board live, computes the candidate digits for every empty cell, applies logical eliminations (naked pairs, pointing pairs), and then finds the next forced move — telling you which cell and why, so you learn the technique rather than just copying a number.
Can I paste in my own Sudoku puzzle to solve?: The solver works on the puzzles you play in the game, not on an imported grid — press Hint at any point and it solves the next step of the board in front of you. Every generated puzzle is guaranteed to have exactly one solution, verified by the backtracking solver behind the generator.
What is Auto Candidate Mode?: It fills in the small pencil-mark candidates for every empty cell automatically and keeps them updated as you place digits, so you can focus on the logic instead of the bookkeeping. You can also switch to Candidate mode with the pencil (✎) button to jot marks yourself.
How does the solver actually work?: The generator and hint engine are backed by a backtracking constraint solver: it tries digits, propagates the row, column and box constraints, and backtracks when a cell has no candidate left. That guarantees each puzzle has a unique solution and lets the hint engine always find the next correct move.
Does it work on mobile?: Yes. The Sudoku game, its hint engine and Auto Candidate Mode are fully responsive and run in any modern mobile browser, so you can play and take hints on a phone or tablet as well as a desktop.