# 天穹数独 · Celestial Sudoku

> Celestial Sudoku (天穹数独) is a free web sudoku game at https://sudoku.liuzhaohan.com with Classic, Jigsaw, Diagonal and Killer sudoku in four difficulties, a daily four-stage challenge, live two-player friend battles, leaderboards and step-by-step tutorials. It runs in any modern browser on phones, tablets and computers with no download or sign-up, works offline once visited, and is available in Simplified Chinese and English.
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> 天穹数独是一款免费的网页数独游戏：经典、不规则（锯齿）、对角线、杀手四种模式，四档难度，每日挑战、好友对战、排行榜和教程；手机电脑浏览器打开即玩，无需下载或注册，支持离线。

The game itself is a JavaScript app at the site root. The pages below are plain HTML that can be read without running scripts.

## Pages / 页面

- [Celestial Sudoku in English](https://sudoku.liuzhaohan.com/en): what the game is, the four modes, daily challenge, friend battles, leaderboards, tutorials and a short FAQ.
- [Game guide (English)](https://sudoku.liuzhaohan.com/guide/en): rules for every mode, difficulty levels and how they are rated, controls and keyboard shortcuts, notes, hints and assists, daily challenge, friend battles, leaderboards and score checks, accounts and privacy, tutorials, offline install, settings and a full FAQ.
- [游戏指南（中文）](https://sudoku.liuzhaohan.com/guide): 四种模式规则、难度、操作与快捷键、候选与提示、每日挑战、好友对战、排行榜与成绩校验、账号与隐私、教程、离线安装、设置和常见问题。
- [天穹数独 / Play the game](https://sudoku.liuzhaohan.com/): the game itself; its static HTML carries a Chinese introduction and FAQ.

## Facts

- Price: free. Playing every solo mode, the daily challenge and friend battles never requires an account.
- Modes: Classic (rows, columns and 3×3 boxes hold 1–9 once); Jigsaw, also called irregular sudoku (nine irregular bold regions replace the boxes); Diagonal, also called Sudoku X (both long diagonals also hold 1–9 once); Killer (dashed cages whose digits add up to the shown total, no repeats in a cage).
- Difficulty: Easy, Medium, Hard, Expert (Medium is the default). Every puzzle has a unique solution and is verified by a human-style logic solver to be solvable without guessing; it is rated by reasoning workload, not just the number of givens (Classic, Jigsaw and Diagonal give 40, 34, 30 and 26 digits).
- Play aids: candidate notes (hold Candidates for two seconds to fill all), 3 hints per game, deduction help in solo games, undo, pause. Entries are never marked wrong and there is no mistake limit.
- Daily challenge: four stages a day (Easy → Expert, each mode once), same for everyone, resets at 00:00 UTC (08:00 Beijing time); past days cannot be made up; streaks and a daily leaderboard.
- Friend battles: two players race on the same puzzle and the first correct solution wins; share a six-character room code or invite link; no account needed; a player offline for 2 minutes in total loses; rooms survive site restarts.
- Leaderboards: fastest time per mode and difficulty, daily progress and daily streak; signed-in players only; the server issues puzzles encrypted and checks answers, time bounds and hint counts, keeping only the first submission per puzzle.
- Tutorials: Learn Sudoku has three tiers (bronze basics for each mode, silver advanced Classic techniques such as locked candidates and pairs, gold X-Wing, Swordfish and XY-Wing practice).
- Accounts: email one-time code or Google sign-in; syncs results and preferences; friends by eight-character friend code; data export and account deletion in Settings.
- Platforms: web browser on iPhone, iPad, Android, Windows, macOS and Linux; installable as a PWA and playable offline after the first visit; full keyboard control and screen-reader support.
- Languages: Simplified Chinese (zh-CN) and English; the first visit follows the browser language.

## Optional

- [LZH's Games](https://games.liuzhaohan.com/): the developer's hub of other web games.