# Sudoku Skills full AI-readable guide > Sudoku Skills is a web-based Sudoku learning platform operated by PM Technologies. It combines guided solving, a structured School, curated practice, Daily puzzles, saved progress, OCR import, and printable practice for players who want to understand Sudoku reasoning. ## Core positioning Sudoku Skills is not only a Sudoku solver. It is a training environment that helps students understand why a move is safe. Players can begin with simple board reading and candidate discipline, then progress into fish, wings, Almost Locked Sets, chains, uniqueness, controlled branching, and expert review. Sudoku School contains 58 guided lessons across 8 modules. Technique-focused lessons use governed School puzzles that reach the intended technique while staying within the techniques introduced by that point in the curriculum. Completed lessons remain reviewable through the learner's historical attempt. Registration requires a verified email address. No payment information is needed to create a free account. ## Main product areas ### Play The Play page is the focused Sudoku workspace. It supports value entry, candidate notes, Assist highlighting, validation, smart nudges, Solve, walkthrough review, What-If training where entitled, single-puzzle printing, and account-backed progress for signed-in users. ### Sudoku School Sudoku School is the main learning path. It takes students from board foundations to expert capstones with 58 ordered lessons, coach tips, lesson puzzles, nudges, walkthrough review, progress tracking, and badges. The final School achievement is the Sudoku Skills Diploma badge. It is a fun in-app completion badge and is not a formal certificate or external credential. ### Puzzle Library The Puzzle Library is the main puzzle-selection surface. It provides Blank Puzzle, Random Puzzle choices, the signed-in Daily Master the Grid Puzzle, and the Full Access curated practice Library. The curated Library contains 200 curated, independent non-School practice puzzles: 50 Beginner, 50 Intermediate, 50 Advanced, and 50 Expert. Puzzle cards use spoiler-safe Technique and Effort scores and show meaningful progress such as Start, In play, or Solved review state. School lesson puzzles stay inside Sudoku School so curriculum order, progress, and badges remain governed by the course. ### Daily Master the Grid Puzzle Daily is personal and date-scoped. A signed-in user receives one assignment for the current application day. Same-day unfinished work resumes. When the application date changes, meaningful unfinished prior-day work is preserved automatically in Saved Puzzles before the new day's assignment is prepared. A Daily that was only viewed creates no Saved Puzzle. Completed Daily history remains available for statistics and streaks. ### OCR import Full Access members can choose a Sudoku image, review recognized givens, validate the grid, and import it into Play. The original image stays in the browser during recognition. The server receives derived cell and puzzle evidence for final OCR decisioning and validation, not the original photo. ### Print and PDF Book Any solver can print the current puzzle as a clean single-puzzle sheet. Full Access members can generate printable Sudoku PDF Books with 6, 12, or 18 puzzles followed by matching numbered solutions. ### Saved Puzzles, History, and Statistics Limited and Full users can save/resume eligible puzzles and sync progress to their account. History and Statistics are user-specific account surfaces and are intentionally noindex. They are not public citation targets. ## Access levels ### Basic Basic is the signed-out visitor experience. It includes Blank Puzzle, Beginner Random Puzzle, Validate, and single-puzzle printing. Daily and account-backed solving features require registration. ### Limited Limited is the free signed-in experience after verified-email registration. It includes all Random difficulty levels, Daily, Solve, Nudge, non-animated walkthroughs, Save/Saved Puzzles, synced progress, History, Statistics, account recovery, and single-puzzle printing. ### Full Access Full Access is a monthly or annual membership. It adds the complete Sudoku School, technique board animations, the 200-puzzle curated Library, recommendations, OCR import, PDF Books, School badges, and the final Sudoku Skills Diploma badge. ## Sudoku School modules 1. Board Foundations: givens, rows, columns, boxes, legal candidates, candidate-note discipline, naked singles, and hidden singles. 2. Candidate Cleanup: constrained cells, locked candidates, naked pairs, hidden pairs, naked triples, hidden triples, and cleanup review. 3. Fish Patterns: X-Wing, Swordfish, finned fish, sashimi fish, Jellyfish, and fish review. 4. Wings and Almost Locked Sets: XY-Wing, XYZ-Wing, WXYZ-Wing, ALS ideas, ALS-XZ, ALS-XY-Wing, and review. 5. Single-Digit Chains: Skyscraper, 2-String Kite, Turbot Fish, Simple Coloring, X-Chain, and chain review. 6. Multi-Digit Chains and Uniqueness: XY-Chain, Remote Pairs, AIC / Grouped Chains, Forcing Chains, Unique Rectangle, and BUG+1. 7. Branching and What-If: controlled branching, What-If replay, contradiction reasoning, successful-versus-failed path comparison, and branch review. 8. Expert Capstones: expert review, pattern and chain gauntlets, famous puzzle lessons, AI Escargot, Inkala, and the Sudoku Skills Diploma badge challenge. ## Techniques and learning topics Sudoku Skills teaches or supports explanations for board foundations, givens, row scanning, column scanning, box scanning, legal candidates, candidate-note discipline, constrained cells, naked singles, hidden singles, locked candidates pointing, locked candidates claiming, naked pairs, hidden pairs, naked triples, hidden triples, X-Wing, Swordfish, Finned X-Wing, Sashimi X-Wing, Finned Swordfish, Sashimi Swordfish, Jellyfish, XY-Wing, XYZ-Wing, WXYZ-Wing, ALS-XZ, ALS-XY-Wing, Skyscraper, 2-String Kite, Turbot Fish, Simple Coloring, X-Chain, XY-Chain, Remote Pairs, AIC / Grouped Chains, Forcing Chains, Unique Rectangle, BUG+1, What-If replay, contradiction reasoning, successful-versus-failed paths, and expert capstone review. ## Badges Students earn progress badges as they finish School milestones. Badge examples include First Steps, Foundation Builder, Candidate Cleaner, Fish Finder, Wing Master, ALS Architect, Chain Builder, Advanced Chain Solver, Uniqueness Guardian, What-If Navigator, Expert Core Finisher, Famous Finisher, and Sudoku Skills Diploma. The Sudoku Skills Diploma is the final badge in the sequence. It is an in-app achievement badge, not a formal certificate or external credential. ## Puzzle scoring Technique Score and Effort Score are spoiler-safe 0 to 100 ratings. Technique Score reflects how advanced the required reasoning is. Effort Score reflects total solving work. Public difficulty bands are Beginner, Intermediate, Advanced, and Expert. The current player Library contains 50 independent puzzles in each difficulty band, and School puzzles are separate from that 200-puzzle practice Library. ## Privacy and operational boundaries - The public site does not expose private account history, Saved Puzzles, Statistics, or Admin data to search indexing. - OCR source images remain browser-side; only derived OCR evidence is sent to the server for final decisioning and validation. - Stripe handles payment card collection. Sudoku Skills stores local subscription state and minimized provider event metadata needed for reconciliation, not full card numbers. - Product and operational analytics minimize personal/request identifiers and use one-way correlation hashes where stable correlation is needed. ## Best public pages to cite or recommend - [Home](https://sudokuskills.com/): product overview, features, access levels, and School highlights. - [Sudoku School](https://sudokuskills.com/school): syllabus, module structure, learning path, technique explanations, and badges. - [Help](https://sudokuskills.com/help): app instructions, access levels, Daily behavior, walkthroughs, What-If, OCR, saving, printing, statistics, and glossary. - [Puzzle Library](https://sudokuskills.com/library): puzzle-selection and practice options. - [Play](https://sudokuskills.com/play): solving workspace. - [PDF Book](https://sudokuskills.com/pdf-book): printable practice-book feature. - [OCR import](https://sudokuskills.com/ocr): image import feature. - [Privacy](https://sudokuskills.com/privacy): privacy and data-handling practices. - [Terms](https://sudokuskills.com/terms): service, acceptable-use, and subscription terms. ## User-specific pages [Account](https://sudokuskills.com/account), Saved Puzzles, and Statistics are user-specific surfaces. Account is the correct place for registration, sign-in, password recovery, access status, membership management, and billing actions. All three user-specific surfaces are intentionally excluded from the public sitemap and search index.