The byes are where brackets go wrong
A knockout bracket needs a power of two. Eleven entrants go into a bracket of sixteen, which leaves five empty slots.
Where those five gaps sit decides the tournament, and there are two ways to get it wrong that both look perfectly reasonable written down.
The first is handing byes to whoever is at the top of the list. That rewards typing order rather than anything anybody earned.
The second is the one that actually causes trouble: putting two byes in the same first-round tie. Now there is a match with nobody in it, and somebody arrives in round two having played no one at all. It is not obvious on the sheet and it is very obvious on the day.
The scrambled-looking order is doing the work
A bracket of eight is laid out 1, 8, 4, 5, 2, 7, 3, 6. It looks arbitrary and it is the opposite.
Seed 1 and seed 2 end up in opposite halves, so they can only meet in the final. The top four land in separate quarters, so no two of them can meet before the semi-finals. Each tie pairs seeds that add up to one more than the bracket size, so the strongest always faces the weakest available.
Lay a bracket out 1 v 2, 3 v 4 instead and you knock the two best entrants out in the first round, which is the thing seeding exists to prevent.
Place the seeds and the byes sort themselves out
Here is the neat part. You do not need a rule for byes at all.
Build the standard order for the bracket size, drop your entrants into it in seed order, and leave the leftover slots empty. The gaps automatically land on the top seeds, and because of how the order pairs up, two gaps can never end up facing each other.
Nothing is checked, corrected or special-cased. It falls out of the ordering, which is why the ordering has survived unchanged for a century.
The count that checks any bracket
Total matches is always one fewer than the number of entrants. Eleven entrants, ten matches. Thirty-three entrants, thirty-two matches.
Every match knocks exactly one person out, and everybody except the eventual winner has to be knocked out. Byes change who plays when; they cannot change that total.
It is worth knowing because it is the fastest way to check a bracket somebody else drew up. Count the matches. If it is not one fewer than the field, something is wrong with it.
Seeded or drawn is a real choice
Seeding uses the order you type, strongest first, and keeps the best apart for as long as the format allows.
A random draw ignores that and can put your two best entrants together in round one. For a knockabout on a Sunday that is part of the fun. For anything with a trophy at the end it means the tournament is decided by the draw rather than by the play, and the draw here is seeded so you can at least reproduce it when somebody complains.
Common questions
Who should get the byes?
The top seeds, and it is not a courtesy. A bracket needs a power of two slots, so eleven entrants go into a bracket of sixteen with five gaps. Those gaps have to be spread so that no two land in the same first-round tie, because that would create a match with nobody in it and send somebody to round two having played no one. Placing seeds in the standard order makes that impossible rather than something you check for afterwards.
How many matches are played altogether?
Always one fewer than the number of entrants, whatever the byes do. Eleven entrants means ten matches. The reason is simple: every match knocks exactly one entrant out, and everybody except the winner has to be knocked out at some point. It is a useful sanity check on any bracket somebody hands you.
Why does the bracket order look scrambled?
Because it is 1, 8, 4, 5, 2, 7, 3, 6 rather than 1 to 8 in order, and that ordering does real work. It puts seed 1 and seed 2 in opposite halves so they can only meet in the final, and the top four in separate quarters so they cannot meet before the semi-finals. Laying a bracket out 1 v 2, 3 v 4 would knock the two best entrants out in round one.
What is wrong with just giving the first few teams a bye?
Two things. It rewards whoever happened to be typed in first rather than whoever earned it, and unless you are careful it can put two byes in the same tie. The second one is the serious version, because it produces an empty match that nobody notices until the day.
Can I draw it at random instead of seeding?
Yes, and the tool will do it from a seed so the draw can be reproduced. Be aware what you are choosing: a random draw can put the two strongest entrants against each other in round one. That is fine for a friendly and a bad idea for anything people care about winning.
How many rounds will it take?
The number of times you can halve the bracket. Sixteen slots is four rounds, thirty-two is five, sixty-four is six. Byes do not add a round, they just mean some entrants skip the first one.