Rules

What is Sudoku Corner?

Sudoku Corner is a competitive sudoku platform where players solve puzzles head-to-head in real time. Both players get the same puzzle and race to finish faster with fewer mistakes. There is an ELO rating, the monthly SC League (Sudoku Corner League) and several game modes.

Game modes

Three divisions

Each division has its own puzzle pool, ELO rating and leaderboard. Puzzles are rated with the Sudoku Explainer (SE) scale, a widely used standard that measures the hardest logical technique a puzzle needs.

SC League

The Sudoku Corner League is the monthly season that runs in all three divisions at once. Every ranked match counts toward your SC League standing.

Duration

One calendar month — a new season starts on the 1st.

Divisions

Beginner, intermediate and expert, each with its own ranking.

Rating reset

SC League ELO resets to 1200 every season. Global ELO never resets.

Champion badge

The top player of each division at season end earns a champion badge.

Standings are always on the leaderboard. Only ranked matches count — friendly and solo games don't change SC League ELO.

XP, levels & streaks

Next to ELO (skill), every player has XP and a level (activity). XP never goes down — every game earns it, win or lose.

• Earn XP from every game; wins, flawless solves and challenges give bonuses.
• Daily streak — play at least one game a day to grow it. Miss a day and it resets.
• Daily goal — pick Casual, Regular or Intense and earn bonus XP when you reach it.

Exact XP values are in Detailed rules.

How a match works

1. Join the queue in a division.
2. Get matched with an opponent.
3. A short countdown starts the match.
4. Both of you solve the same puzzle.
5. The faster effective time wins (or more progress if nobody finishes).

Each error adds a 15-second penalty to your final time, and hints add penalties too. Reach the error limit and you lose the match.

Ranked matches

Both players solve the identical puzzle at the same time. The match ends when both finish, when one player reaches the error limit, or when the catch-up time runs out.

Matchmaking

The queue looks for an opponent with a similar rating. If no human is available you may be matched with a bot of a similar level; bots play like humans during the match.

Winning

Each player's total time is their own solve time plus their own penalties (errors and hints). If both players finish, the lower total time wins; equal totals are a draw. If only one finishes, that player wins. If neither finishes, more correct cells wins; equal progress is a draw.

Catch-up time

Finishing first does not end the match straight away if you collected penalties: the other player can still win by finishing with a lower total time. They keep playing exactly as long as that is still possible — your penalties minus their own — plus 3 seconds for network delay. If they cannot catch up any more, the match ends right away; when the time runs out, the player who finished wins.

Errors & penalties

A wrong digit counts as an error: it turns red and is removed. Each error adds 15 seconds to your effective time. Reaching the limit ends the match as a loss.

Hints

Hint types

Each hint uses one of your hints and adds its penalty to your effective time, on top of error penalties.

ELO rating & seasons

Every player has two ratings per division:

• Global ELO — your all-time skill. Never resets; starts at 1200.
• SC League ELO — resets at the start of every monthly season and decides the SC League ranking and the champion.

Changes follow the standard ELO formula. Players with fewer than 30 rated games use K = 40 so their rating moves quickly; after that K = 20. Beating a stronger opponent gains more, losing to a weaker one costs more, and a draw moves the rating a little depending on the difference.

The ELO system in detail — formulas, examples and tips

XP, levels & streaks

XP measures how active you are (ELO measures how good). XP is only ever gained, so a losing streak never sets your level back.

How you earn XP

Bonuses stack: a flawless ranked win earns 20 + 15 + 10 = 45 XP.

Levels

Your level comes from total XP. Each level needs a bit more than the last, so early levels come fast and high levels are a real achievement.

Daily streak

Your daily streak counts days in a row with at least one game — any mode counts. Miss a full day and it starts again from 1 with your next game. It is not the same as your win streak (matches won in a row).

Streak milestones

Daily goal

Set your daily XP target in Settings → Preferences. Reaching it gives a one-time bonus that day:

The goal is optional; the streak only needs one game a day.

Streak reminders

In the Android app you can turn on a streak reminder (Settings → Preferences): if your streak is alive and you haven't played yet, a notification arrives an hour before midnight.

SC League — Sudoku Corner League

The official monthly competition. Every calendar month a new season begins, standings are wiped and players compete afresh in their division.

Season structure

A season runs from the 1st to the last day of the month. At midnight UTC on the 1st all SC League ELO resets; Global ELO is not affected. The three divisions run side by side and you have a separate SC League ranking in each division you play ranked in.

How rankings work

Your position depends only on your SC League ELO in that division. It starts at 1200 each season and follows the same formula as Global ELO. Only ranked matches count; friendly and training games don't.

Leaderboard

The leaderboard shows the top players of each division live, with season, all-time and weekly views. Your own position is highlighted when you are logged in.

Season end & rewards

When a season ends the standings are locked. The #1 player of each division earns that season's champion badge — permanent, on the profile and in the badge collection.

Tips to climb

Everyone starts level each month. Early wins move your rating faster while you have played fewer games, and steady play through the month beats a late burst. Play in the division that matches your skill — if you are often outplayed, build up in Training first.

Solo sudoku

Play on your own with no rating impact: any division, unlimited puzzles, the same hint and error limits as ranked. Solo results don't go to the ranked leaderboards. Puzzles come from the same pool as ranked puzzles, so the difficulty is consistent.

Friendly challenges

Challenge anyone on your friends list. You both solve the same puzzle as in ranked — same error limits, hint limits and penalties — but no ELO changes. Challenges are sent from the friends page; the other player can accept or decline, and the match starts once they accept.

Daily challenges

Every day at midnight UTC there is a new puzzle in each division, the same for everyone, one attempt per division. The daily leaderboard ranks completion time including penalties. Past days are in the archive; archive results don't count.

Fair play & anti-cheat

Every match is analysed for suspicious patterns: solve speed against puzzle difficulty, error patterns, move timing and statistics across matches. Suspicious results are flagged and can be annulled — the rating changes are then reversed.

What counts as cheating

Any external solver or solver extension, copying the puzzle into another tool, using several accounts to manipulate ratings, disconnecting on purpose to avoid a loss, or colluding with an opponent. The built-in hints are always allowed.

Consequences

From a warning to a temporary suspension to a permanent ban. Banned accounts lose ratings, badges and SC League standings. If you think a ban was a mistake, contact support.

Controls

Tap or click a cell, then enter a digit. On a keyboard:

Puzzle difficulty & SE rating

All puzzles are rated with the Sudoku Explainer (SE) scale, common in competitive sudoku. It reflects the hardest technique needed. Puzzles come from the Sudoku Exchange Puzzle Bank, pre-rated by SukakuExplainer.

More: SukakuExplainer on GitHub · QQWing puzzle generator