What is a Sudoku solver?
A Sudoku solver is a tool that takes a partially filled 9×9 grid and either completes it or shows the next logical placement. Most online solvers only dump the finished grid. Zeloku does both: a one-click Solve for when you need the answer, and a Hint engine that names the technique — so you learn the pattern instead of just copying digits.
How to use this free Sudoku solver
- Enter the puzzle. Click any cell and type 1–9, or paste an 81-character string (use
0or.for empty cells). Click Load sample puzzle if you just want to see the engine work. - Ask for a Hint. The solver scans for the cheapest human technique that places a digit, highlights the cell, and explains why.
- Or press Solve. Uniqueness is checked first. If the board has exactly one solution, every empty cell fills in sage green so you can tell givens from answers.
- Learn the move. Open the matching page in the techniques library and study an annotated example of the same pattern.
Fast answer or step-by-step solution?
Choose Solve when you need the answer quickly. Choose Hint when you want to understand the board: it reveals one logical move at a time, names the technique, and explains why the digit is allowed. That makes this a useful fast Sudoku solver for checking a puzzle as well as a step-by-step solver for learning how to finish it yourself.
Techniques this Sudoku solver knows
Hints are attempted in pedagogical order — easiest first — so the move you see is usually the one a careful human would find next:
- Naked Single — only one candidate left in a cell
- Hidden Single — a digit has only one legal home in a unit
- Naked Pair — two cells share the same two candidates
- Pointing Pair — a box locks a digit into one line
- X-Wing — a rectangular digit pattern that eliminates candidates
Harder patterns (Swordfish, full chain reasoning) fall through to Solve when no simple step remains. The engine will say so rather than invent a guess.
Sudoku solver vs. playing the daily puzzle
Use the Sudoku solver when you have a puzzle from a newspaper, app or friend and want either the answer or a nudge. Use the daily Sudoku when you want a fresh, rated board with a timer, mistake tracking and a win card. Same engine underneath; different job.
Why Zeloku's Sudoku solver is different
- Explains, doesn't just fill. Technique name + plain-English reason on every Hint.
- Uniqueness-aware. Flags zero-solution and multi-solution boards instead of silently lying.
- Runs in your browser. No account and no upload of your puzzle to a server queue or external API.
- Tied to a real library. Every technique the solver names has a long-form page with diagrams.
- Free, forever. No freemium gate on Solve or Hint.
Tips for getting better with a solver
- On a stuck board, take one Hint, write the digit yourself, then try to find the next move unassisted.
- When a technique name is new, open its library page before taking the next Hint.
- If Solve reports multiple solutions, your givens are incomplete or mistyped — fix the source puzzle, don't trust the fill.
- For learning from scratch, start with how to play Sudoku and an Easy board, then come back to the solver when you stall.