Game Rules

What is Sudoku Corner?

Sudoku Corner is a competitive Sudoku platform where players solve puzzles head-to-head in real time. Both players receive the same puzzle and race to complete it faster with fewer mistakes. The platform features an ELO rating system, the monthly SC League (Sudoku Corner League), and multiple game modes.

Game Modes

Three Divisions

Each division has its own puzzle pool, ELO rating, and leaderboard. Puzzles are rated using the Sudoku Explainer (SE) rating system — a widely recognised standard measuring the hardest logical technique required to solve the puzzle.

SC League

The Sudoku Corner League (SC League) is the monthly competitive season that runs across all three divisions simultaneously. Every ranked match you play counts toward your SC League standing.

Current standings are always visible on the leaderboard. Only ranked matches count — friendly and training games do not affect SC League ELO.

How a Match Works

1. Queue for a division → 2. Get matched with an opponent → 3. Countdown 3-2-1 → 4. Both solve the same puzzle → 5. Winner is the player who finishes first (or has more progress if time runs out).

If you make an error, a 15-second time penalty is added to your final time. Using hints also adds time penalties. Reach the maximum number of errors and you forfeit the match.

Ranked Matches

Ranked matches are the core competitive mode. Both players solve the identical puzzle simultaneously. The match is resolved when both players finish, one player reaches maximum errors, or the grace window expires.

Matchmaking

When you queue for a division, the system finds an opponent with a similar ELO rating. If no human opponent is available, you may be matched against a bot of appropriate skill level. Bots are indistinguishable from human players during the match.

Winning Conditions

If both players complete the puzzle, the one with the faster effective time wins. Effective time equals your solve time plus penalties. If only one player completes the puzzle, they win. If neither completes it, the player with more correct cells wins. If both have equal progress, it's a draw.

Grace Window

When the first player finishes, the second player gets a 60-second grace window to also complete the puzzle. If they don't finish in time, the match is resolved based on current progress.

Errors & Penalties

Error Limits per Division

When you place an incorrect digit, it counts as an error. The cell is marked red and the digit is removed. Each error adds a 15-second penalty to your effective time. Reaching the maximum number of errors instantly forfeits the match.

Hints

Hint Limits per Division

Hint Types & Time Penalties

Each hint used consumes one of your available hints and adds the corresponding time penalty to your effective solve time. Hint penalties are added on top of error penalties.

ELO Rating & Seasons

Dual Rating System

Every player has two ELO ratings per division:

Global ELO — tracks your all-time skill. Never resets. Starts at 1200.

SC League ELO — resets at the start of each monthly SC League season. Used for the SC League leaderboard and determining the season champion.

How ELO Works

ELO changes are calculated using a standard formula. New players (fewer than 10 games) have a K-factor of 40, meaning their rating moves quickly. Established players use K=20 for more stable ratings.

Beating a higher-rated opponent gains more ELO than beating a lower-rated one. Losing to a lower-rated opponent costs more ELO. Draws give a small gain or loss depending on the rating difference.

Learn more about the ELO system — formulas, examples & tips

SC League — Sudoku Corner League

The Sudoku Corner League is the official monthly competition of Sudoku Corner. Every calendar month a new season begins, standings are wiped, and players compete fresh for glory in their division.

Season Structure

Each season runs for exactly one calendar month — from the 1st to the last day. At midnight UTC on the 1st, all SC League ELO scores reset and the race begins again. Your Global ELO is never affected by the reset.

Three divisions run simultaneously — Beginner, Intermediate, and Expert. You have an independent SC League ranking in every division you have played ranked matches in during the current season. Playing more matches in a division means a more accurate ranking and a better chance to climb.

How Rankings Work

Your position in the SC League is determined solely by your SC League ELO in that division — the higher the better. SC League ELO starts at 1200 at the beginning of every season and moves up or down with each ranked result, following the same ELO formula as Global ELO. Beating stronger opponents earns more points; losing to weaker ones costs more.

Only ranked matches affect your SC League ELO and standing. Friendly games and training sessions have no impact. Draws count as a fractional gain or loss depending on the ELO difference between the two players.

Leaderboard

The SC League leaderboard shows the top players for each division in real time. You can switch between the current season view and the all-time Global ELO view. Your own rank and SC League ELO are highlighted when you are logged in.

Season End & Rewards

When a season ends, the standings are locked. The #1 player in each division earns an exclusive Champion badge for that season. The badge is permanently attached to that player's profile and badge collection — it cannot be lost or overwritten by future seasons. Every season creates three new unique champion badges (one per division), so collectors can accumulate them over time.

Tips to Climb the SC League

Because SC League ELO resets every month, every player starts on equal footing. Early wins give you an ELO advantage since the K-factor is higher at the start (fewer games played = faster movement). Playing consistently throughout the month beats a late burst — opponents in the lower half of the leaderboard have less to gain. Playing in a division where your real skill matches the puzzle difficulty is key: if you are consistently outplayed, consider building skill in Training before queuing ranked.

Training Mode

Training mode lets you practice solo with no rating impact. You can choose any division and play unlimited puzzles. Training uses the same hint and error limits as ranked matches. Your training results are not tracked on leaderboards.

Training puzzles come from the same pool as ranked puzzles (puzzles that have already been used in ranked matches). This ensures consistent difficulty.

Friendly Challenges

You can challenge any player on your friends list to a friendly match. Both players solve the same puzzle just like in ranked, but with no ELO changes. The same error limits, hint limits, and time penalties apply.

Friendly challenges are sent via the player's profile or friends list. The challenged player can accept or decline. If they're online, the match starts immediately after acceptance.

Daily Challenges

Every day at midnight UTC, a new puzzle is generated for each division. All players solve the same puzzle that day. You get one attempt per division — no retries. The daily leaderboard ranks players by completion time (including penalties).

Missed a day? Past daily challenges are available in the archive, but archive results don't count for the daily leaderboard.

Fair Play & Anti-Cheat

Sudoku Corner takes competitive integrity seriously. Every match is analyzed for suspicious patterns.

What We Monitor

Our anti-cheat system analyzes solve speed relative to puzzle difficulty, error patterns, move timing consistency, and statistical anomalies across multiple matches. Suspiciously fast completions or inhuman accuracy patterns are automatically flagged for review.

Consequences

Players found to be cheating — using solvers, bots, browser extensions, or any other external assistance — will face consequences escalating from a warning to a temporary suspension to a permanent ban. Banned accounts lose all ratings, badges, and SC League standings.

If you believe you were banned unfairly, you can appeal by contacting support.

What Counts as Cheating

Using any external Sudoku solver or solver extension, copying the puzzle into another tool, using multiple accounts to manipulate ratings, intentionally disconnecting to avoid a loss, or any form of collusion with opponents. Using the built-in hints is always allowed — that's what they're for.

Controls

Click or tap a cell to select it, then enter a digit 1-9. You can also use keyboard shortcuts:

Puzzle Difficulty & SE Rating

All puzzles on Sudoku Corner are rated using the Sudoku Explainer (SE) rating — a standard widely used in the competitive Sudoku community. The SE rating reflects the hardest logical technique required to solve the puzzle. Puzzles come from the Sudoku Exchange Puzzle Bank, pre-rated by SukakuExplainer.

Learn more: SukakuExplainer on GitHub · QQWing puzzle generator