Swiss Tournament Pairing
Pairs each round by backtracking search, so nobody meets twice while a rematch-free pairing exists — and it says so plainly when one does not.
Rounds
Standings
How the pairing is decided
- Not playing the same opponent twice is a CONSTRAINT, not a preference, and that is what breaks naive pairing. Walking down the standings and pairing each player with the next available one works for a few rounds and then paints itself into a corner, leaving the last two having already met and no way back.
- So this searches with backtracking instead: take the highest unpaired player, try their opponents closest-score-first, and undo the choice if the rest of the field then cannot be paired. In an odd field the player sitting out is part of that search rather than settled before it, because fixing the bye first can rule out the only arrangement that works. Together those find a rematch-free pairing whenever one exists.
- Within a score group the field is split in half and the top of one half plays the top of the other — 1 against 4, 2 against 5, 3 against 6. Pairing neighbours instead is a different system, gives duller games, and runs out of fresh opponents markedly sooner.
- When no such pairing exists, it says so rather than silently repeating a game. In a field of N players there are only about N-1 rounds available before rematches become unavoidable, and pretending otherwise is how a tournament ends in an argument.
- Colours are assigned after the pairing, never during it. A correct pairing that gives someone an awkward colour is better than a wrong pairing with tidy colours — so who plays whom is settled first, then whoever is further behind on whites takes them.
- The bye goes to the lowest-placed player who has not already had one. Handing someone a second bye while another player has had none is the one thing every competitor notices — but it yields to the rematch rule, which is a rule rather than a courtesy. If every pairing with the preferred player sitting out would repeat a game, the bye moves to the next candidate and the reason is printed with the round, so it can be explained to whoever asks.
- Every tie is broken by rating and then by name, so the same standings always produce the same pairings. A pairing you cannot reproduce is a pairing you cannot defend.
How to use
- Add your players with a rating or seed number.
- Pair the round, play it, and enter the results.
- Pair the next one — the history is taken into account automatically.
Frequently asked questions
Why is pairing harder than it looks?
Because not repeating an opponent is a constraint rather than a preference. Walking down the standings and pairing each player with the next available one works for a few rounds and then paints itself into a corner, leaving the last two having already met and nothing left to swap. This searches with backtracking instead, so it finds a rematch-free pairing whenever one exists.
What happens when a rematch is unavoidable?
It says so, rather than repeating a game quietly. A field of N players only has about N-1 rounds in it before everyone has met everyone, and pretending otherwise is how a tournament ends in an argument. You still get a full pairing — you just also get told.
How many rounds should I run?
Roughly the base-two logarithm of the field: three rounds for eight players, four for sixteen, five for thirty-two. That is what it takes to separate a single winner. The tool shows both that figure and the hard limit before rematches become unavoidable.
How are players within a score group paired?
The group is split in half and the top of one half plays the top of the other — first against fourth, second against fifth. Pairing neighbours instead is a different system, produces duller games, and runs out of fresh opponents noticeably sooner.
Who gets the bye?
The lowest-placed player who has not already had one. Handing someone a second bye while another player has had none is the one thing every competitor notices. A bye is worth a full point and does not count as having played anyone.
How are colours decided?
After the pairing, never during it. A correct pairing that gives someone an awkward colour is better than a wrong pairing with tidy colours, so who plays whom is settled first and then whoever is further behind on whites takes them. Anyone drifting more than two colours out of balance is flagged.
Will the same standings always pair the same way?
Yes. Every tie is broken by rating and then by name, so the result is completely reproducible — which matters, because a pairing you cannot reproduce is a pairing you cannot defend when somebody questions it.
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