The wider Sudoku ecosystem

This list covers complementary resources — places to learn the theory, verify a grid, generate puzzles, or read how a technique works. We leave out direct classic-Sudoku play apps on purpose: this page is a map of the surrounding ecosystem, not a directory of where else to play. Several entries (HoDoKu, the SE grade tools) are the same authorities our own difficulty scale is built on.

The 'learn the theory' tier — encyclopedias of solving techniques and terminology.

• SudokuWiki.org (Andrew Stuart)

  Andrew Stuart's long-running reference documenting 40+ solving strategies, from singles to extreme techniques, alongside a step-by-step logical solver that shows the reasoning square by square. The canonical 'how this technique works' explainer.

• Sudopedia

  'The Free Sudoku Reference Guide' — a community wiki of terminology, technique indexes (basic to advanced), notation, and the mathematics of Sudoku. Widely regarded as the best single index of technique names.

• HoDoKu

  A free desktop generator/solver/analyzer that implements more human-style techniques than almost any other program, with docs that double as a top-tier technique reference. An offline study tool, not an online play destination.

• Glossary of Sudoku (Wikipedia)

  Neutral encyclopedic definitions of Sudoku terms plus an overview of solving algorithms (backtracking, constraint propagation). A good 'what does this word mean' starting point.

Paste a grid, read the logical solve path — tools for verifying and understanding puzzles.

• SudokuSolver (dclamage / Rangsk)

  A fast solver supporting all common variants with a logical solve path using human-like techniques; imports common formats and counts solutions for uniqueness checking. A constructor/analyst tool, especially for variant Sudoku.

• Simple Sudoku (Angus Johnson)

  Classic freeware Windows generator, helper, and solver that produces symmetric, unique-solution, no-guessing puzzles across five tiers. Historically significant — origin of the 'SSTS' technique set.

Developer/infrastructure tools for producing and rating puzzles in bulk.

• QQWing

  A fast open-source command-line generator and solver that rates difficulty, prints solve instructions, and generates around 1000 puzzles per second. Used as a building block in many projects.

• tdoku

  A very fast solver and generator with a benchmark suite comparing the fastest known solvers. Pure performance/research tooling for engineers and researchers.

The reference engines that define the SE grade our trainer is built around — honest provenance for our difficulty claims.

• Sudoku Explainer (community forks)

  The reference program that assigns the 'SE' difficulty rating by finding the hardest technique a puzzle forces (SE 9.0+ marks the monsters). It is the upstream authority for the very grade our trainer exposes.

• SukakuExplainer (pencilmark variant)

  A community-maintained fork of Sudoku Explainer adding speed, a GUI, and pencilmark support, plus a documented technique-to-SE-value table (e.g. dynamic forcing chains land around SE 8.8–9.6).

Setters' tools kept as TOOLS, not play destinations — they serve makers, not classic players.

• f-puzzles (Sudoku Setter)

  The dominant browser-based constructor for Sudoku and variant Sudoku, used heavily by setters to build, validate, and share puzzles. A creation tool for authors, not a curated play ladder.

• Sven's SudokuPad

  The variant-Sudoku player/renderer used to present puzzles set by others; imports puzzles built in f-puzzles. We list it as infrastructure for the variant-setting ecosystem — a different audience than our classic trainer.

Where the advanced solving techniques were invented and named.

• The New Sudoku Players' Forum (enjoysudoku)

  The historically most important Sudoku community and the research wellspring of hard-Sudoku theory — where most advanced techniques were first developed, and home to the hardest-puzzle hunts. A discussion forum, not a play product.

Non-commercial, non-competing FOSS toolkits worth knowing about.

• Simon Tatham's Portable Puzzle Collection — 'Solo'

  A free, MIT-licensed collection of 40 logic puzzles; 'Solo' is its Sudoku generator. A hobbyist FOSS toolkit with no accounts, ranking, or SE grading — referenced as an open-source curiosity, not a trainer.