Sudoku Printable

Free printable Sudoku puzzle generator with 19 variant types, 4 grid sizes, 4 difficulty levels, and instant PDF download. No signup, fully client-side.

Live Site: sudokuprintable.me

Table of Contents

• Features
• Sudoku Variants
• Grid Sizes & Difficulty
• Paper Sizes
• Tech Stack
• Architecture
• Plugin System
• Puzzle Engine
• PDF Generation
• Adding a New Variant
• Project Structure
• Getting Started
• Testing
• SEO
• License

Features

• 19 Sudoku variants — from Standard to Killer, Jigsaw, Thermo and more
• 4 grid sizes — 4×4, 6×6, 9×9, and 16×16 (details)
• 4 difficulty levels — Easy, Medium, Hard, Evil (details)
• Batch generation — create 1, 4, 6, 9, 12, or 24 puzzles at once
• Answer keys — None, Append (solutions after puzzles), or Only (answers only)
• Live paper preview — see exactly what will print before downloading
• High-quality PDF — vector output via pdf-lib, sharp at any DPI
• Direct print — send puzzles straight to printer without saving a file
• Large Print mode — bigger grids for accessibility and low-vision users
• Font size control — Small / Medium / Large number sizing
• 6 paper sizes — Letter, A4, A5, Legal, Tabloid, A3 (full list)
• 100% client-side — all generation and rendering happens in the browser

Sudoku Variants

19 rule variants, each implemented as a self-contained plugin:

Variant	Description
Standard	Classic Sudoku — rows, columns, and boxes
Diagonal	Both main diagonals must also contain all digits
Windoku	Four extra shaded "window" boxes as constraints
Odd-Even	Shaded cells must contain odd or even numbers
Knight	No two identical digits a chess knight's move apart
King	No two identical digits a chess king's move apart
Jigsaw	Irregular-shaped regions replace standard boxes
Non-Consecutive	Adjacent cells can't hold consecutive numbers
Disjoint	Same position across all boxes must contain unique digits
Center Dot	Center cells of all boxes form an extra group
Asterisk	Nine marked cells must contain digits 1–9
Kropki	Dot clues between cells indicate ratio or difference
Consecutive	Bars mark pairs of consecutive numbers
Sandwich	Clues show sum of digits between 1 and 9 in each row/column
Thermo	Digits increase along thermometer paths
Arrow	Digits along an arrow sum to the circle cell
Killer	Cages with sum clues, no repeated digits within a cage
Skyscraper	Edge clues count visible "skyscrapers" from that direction
Greater Than	Inequality signs between adjacent cells

Grid Sizes & Difficulty

Grid Sizes

Size	Digits	Use Case
4×4	1–4	Young kids (ages 5–8), absolute beginners
6×6	1–6	Kids and warm-up puzzles
9×9	1–9	Standard format, all difficulty levels
16×16	1–16 (A–G)	Advanced challenge (beta)

Difficulty Levels

Level	Clues (9×9)	Description
Easy	36–40	Simple logic, no guessing needed
Medium	32–35	Moderate concentration required
Hard	< 31	Advanced elimination techniques
Evil	Minimal	Complex deduction chains, expert only

Paper Sizes

Size	Dimensions
Letter	8.5 × 11 in
A4	210 × 297 mm
A5	148 × 210 mm
Legal	8.5 × 14 in
Tabloid	11 × 17 in
A3	297 × 420 mm

Tech Stack

Layer	Technology	Role
Puzzle Logic	Vanilla JavaScript	Puzzle engine with backtracking solver
PDF	pdf-lib	Vector PDF generation with embedded fonts
Fonts	Fraunces + Manrope	Headings and body typography
Testing	Manual test suite	test-logic.js for engine validation

Architecture

Plugin System

The app uses a plugin registry pattern — identical to the Graph Paper project's approach:

• js/puzzle-types.js — plugin registry with PuzzleTypes.register() / PuzzleTypes.get()
• js/variants/*.js — one self-contained file per variant
• js/app.js — UI controller, preview rendering, state management
• js/pdf-gen.js — PDF layout and rendering

Puzzle Engine

js/puzzle-engine.js provides core generation primitives:

• Base grid generation — mathematically valid grid via formula-based construction
• Randomization — structure-preserving permutations (band/row/stack shuffle + digit relabeling)
• Constraint validation — isValid() accepts an optional extraCheck callback so variants inject custom rules without modifying the engine
• Unique solution enforcement — countSolutions() with backtracking ensures exactly one valid solution
• Clue removal — removeNumbers() strips cells while maintaining solvability, respecting difficulty targets

PDF Generation

js/pdf-gen.js uses pdf-lib for vector PDF output:

• Adaptive layout — auto-calculates puzzles per page based on grid size, paper size, and large-print mode
• Each variant can hook into pdfBackground() and pdfForeground() for custom decorations (shaded regions, thermometer paths, cage outlines, etc.)
• 16×16 grids use hex labels (A–G for 10–16)
• Answer pages rendered with filled grids in lighter styling

Adding a New Variant

1. Create js/variants/my-variant.js
2. Call PuzzleTypes.register({ id, label, description, supportedSizes, generate, ... })
3. Add <script src="js/variants/my-variant.js"></script> in index.html

No changes to puzzle-engine.js, puzzle-types.js, or app.js required.

Project Structure

sudoku-printable/
├── index.html                  # Single-page application
├── css/
│   └── style.css               # All styles
├── js/
│   ├── puzzle-engine.js        # Core generation engine (grid, solver, clue removal)
│   ├── puzzle-types.js         # Variant plugin registry
│   ├── app.js                  # UI controller (preview, state, event handling)
│   ├── pdf-gen.js              # PDF generation via pdf-lib
│   ├── variants/               # One file per Sudoku variant (19 plugins)
│   │   ├── standard.js
│   │   ├── diagonal.js
│   │   ├── killer.js
│   │   ├── jigsaw.js
│   │   ├── thermo.js
│   │   └── ... (19 total)
│   └── vendor/
│       └── pdf-lib.min.js      # Bundled pdf-lib with CDN fallback
├── favicon.svg
├── robots.txt
├── sitemap.xml
├── test-logic.js               # Engine logic test suite
└── test-all-controls.html      # Manual UI control test page

Getting Started

No build step required. Open index.html directly in a browser:

# Option 1: direct open
open index.html

# Option 2: any static server
npx serve .

All puzzle generation runs client-side — no network requests needed (pdf-lib is bundled locally with a CDN fallback).

Testing

• test-logic.js — automated engine tests covering grid generation, constraint validation, solution uniqueness, and clue removal across all grid sizes
• test-all-controls.html — manual UI test page for verifying all controls, settings combinations, and variant rendering

SEO

• JSON-LD structured data — WebApplication + FAQPage (7 questions)
• Semantic content sections — difficulty guide, kids/students guide, grid sizes, benefits
• Canonical URL, Open Graph, and Twitter Card meta
• Sitemap and robots.txt

License

ISC