BLOG
Puzzle design, technique, and the GridJoy story
Writing about the puzzles we build, the techniques behind them, and the choices that shaped GridJoy.
May 2026 · 5 MIN READ
Sudoku vs Killer Sudoku: Which should you actually start with? →
They share the same grid and the same three rules. Here's the honest answer to which one fits where you are right now.
May 2026 · 4 MIN READ
The Rule of 45: Killer Sudoku's most elegant trick →
Every row, column, and box in a 9×9 grid sums to exactly 45. That single fact unlocks most hard Killer puzzles.
May 2026 · 4 MIN READ
Hex Mazes: Why six neighbours change everything →
Square mazes have four choices at every junction. Hexagonal mazes have six — and that difference reaches much deeper than it sounds.
May 2026 · 5 MIN READ
What makes a puzzle game wordless? →
GridJoy uses only numbers. No instructions in any language. Here's why that constraint was the best product decision we made.
May 2026 · 4 MIN READ
Why we built Arena mode →
Puzzle games are usually solitary. We wanted to share the moment of solving with someone specific — not a random leaderboard, a challenge.
May 2026 · 6 MIN READ
Why you keep getting stuck at Sudoku — and how to fix it →
Most Sudoku plateaus come from the same three reasoning errors. Here's what they are, and the technique ladder that clears them.
May 2026 · 6 MIN READ
How to solve Kakuro: a beginner's guide →
Kakuro looks like arithmetic. It's actually a constraint puzzle. Two insights unlock it — and once you see them, every puzzle opens up.
May 2026 · 7 MIN READ
Kakuro strategy: the techniques that break hard puzzles →
Combination narrowing, locked sets, and sum-region arithmetic — the four tools that restart the cascade when easy Kakuro techniques run out.
May 2026 · 7 MIN READ
Number puzzles for adults — a guide to every type →
From Sudoku to Hex Mazes — every major number puzzle type explained, with help choosing the right one for you.
May 2026 · 5 MIN READ
Calcudoku vs KenKen: the same puzzle, a clearer name →
KenKen and Calcudoku are identical puzzles — and once you stop calculating and start deducing cage candidates, both become a lot easier.
May 2026 · 5 MIN READ
Skyscraper puzzles: the Sudoku you see from outside →
Every number is a building, every edge clue counts what's visible. One extra rule on top of Sudoku — remarkably different logic.
May 2026 · 5 MIN READ
Hitori: three rules, surprisingly complex logic →
Shade duplicates. No two shaded cells can touch. All white cells stay connected. Three rules — and from them, cascades that rival puzzles with far more constraints.
May 2026 · 4 MIN READ
Sumplete: why deletion beats placement →
Most number puzzles ask you to fill a grid. Sumplete gives you a full grid and asks you to delete from it — and that reversal makes forced moves faster to spot.
May 2026 · 5 MIN READ
Countdown numbers game: how to find a route to any target →
Trial-and-error loses to the clock. Large × small scan, round-number proximity, fine-tuning — a systematic approach that finds most routes in under 30 seconds.
May 2026 · 5 MIN READ
Futoshiki: the puzzle where cells tell each other which is bigger →
Instead of given digits, Futoshiki gives you < and > signs between cells. Those relational clues chain into forced placements — often faster than Sudoku givens.
May 2026 · 4 MIN READ
Takuzu / Binairo: the binary logic puzzle explained →
Fill a grid with 0s and 1s. Three constraints — no three in a row, balanced rows, no duplicate rows — cascade into elegant forced placements.
May 2026 · 4 MIN READ
Hidato (Starlink): the consecutive-path number puzzle →
Fill every cell with a chain of consecutive numbers — each touching the next. Gap analysis and corner constraints unlock it.
May 2026 · 4 MIN READ
Shikaku: the rectangle-division puzzle explained →
Factor the clue, find the only rectangle that fits, place it. Purely spatial logic — no digit placement, no arithmetic.
May 2026 · 4 MIN READ
Number Mazes: the sequential path puzzle explained →
Anchor from given numbers, count cells between clues, let dead-ends reveal the path — no arithmetic, pure path logic.
May 2026 · 4 MIN READ
Square Maze: the rectangular number-path puzzle →
Corner cells have exactly 2 neighbours — they force first moves before any gap counting on the rectangular grid.
May 2026 · 4 MIN READ
Circular Maze: the concentric-ring number-path puzzle →
The inner ring is the tightest bottleneck — solve it first and the outer rings follow.
May 2026 · 4 MIN READ
Number Crossword: the arithmetic crossword puzzle →
Arithmetic expressions as across clues — evaluate first, match digit count to run length, propagate shared cells.
May 2026 · 4 MIN READ
Number Blocks: the sum-grid puzzle explained →
Fill an empty grid with digits 1–9 so every row and column hits its target sum. One-empty-cell rows give forced digits instantly.
May 2026 · 7 MIN READ
How to solve hard Sudoku: the techniques worth learning →
When elimination stalls, you need naked pairs, hidden pairs, box-line reduction, and X-Wing. Here's how each one actually works.
May 2026 · 7 MIN READ
Killer Sudoku strategy: how to solve it from scratch →
Killer Sudoku looks harder than it is. Forced combinations, Rule of 45, and cage overlap solve most puzzles without guessing — here's how.
May 2026 · 6 MIN READ
Calcudoku strategy: how to solve it without guessing →
Calcudoku looks like arithmetic practice. It isn't. Forced results, subtraction pairs, and cross-referencing solve most puzzles — no guessing needed.
PLAY THE PUZZLES — FREE ON ANDROID
FREE ON GOOGLE PLAY →