If something here is unclear, support will answer in plain language.
Getting started
Why do I have to connect a Lichess account?
Because prizes go to a verified person, not a username someone typed into a form. The link is how we confirm who you are, check that you meet a tournament’s rating limits, and make sure the seat you paid for is yours. Without it we can’t let you buy tournament access.
Do you see my Lichess password?
No. You authorise on Lichess’s own page and we never see, receive or store your password. We also cannot play games as you or read your private messages.
Can I use two Lichess accounts?
No. A Lichess account can be linked to exactly one Chess4prize account. This is what stops someone entering a rating-capped tournament more than once.
Is Chess4prize affiliated with Lichess?
No. Lichess is an independent, free, donation-funded chess platform. We use their public API to run tournaments there. We are not endorsed by or connected to them.
Entering a tournament
Where do the games actually happen?
On Lichess. Chess4prize does not run a chess server or a board. We handle registration, eligibility, results and prizes; Lichess handles the chess.
How do you stop people who didn’t pay from joining?
Two independent locks. Your Lichess username is added to the tournament’s entry list when your seat is confirmed, and Lichess refuses anyone who is not on it. On top of that, each player gets a personal entry code tied to their own Lichess account — it is computed from that account’s name, so it simply does not work for anyone else. Sharing the tournament link, or a screenshot of your code, lets nobody in.
What happens if my rating changes before the tournament?
Eligibility is checked again when payment is confirmed. If that check fails, your entry is held for review and the fee is returned if you cannot be admitted — you are never charged for a seat you were not given. A rating that moves after you have legitimately been admitted does not remove you from the tournament.
What if I close the payment page halfway through?
Nothing is charged and your seat is held as unpaid. Return to the tournament page and you’ll see a button to finish paying — you will not be charged twice.
During and after
How quickly do standings update?
Every few seconds while a tournament is live. We read the tournament centrally and serve the same copy to everyone, which is why the page stays fast even with thousands watching. Each page shows when the standings were last confirmed.
What if Lichess goes down mid-tournament?
The page keeps showing the last confirmed standings and tells you they are paused, rather than presenting stale numbers as current. Syncing resumes automatically once the connection returns.
When do I get paid?
After the tournament is settled and the fair-play check on the winning accounts has run and answered. Every prize is approved by a person before it is paid, and the payout itself is made by hand rather than automatically — there is no wallet and no stored balance. The status is tracked in your results history. We have not committed to a maximum time between a tournament finishing and a prize being paid, and we would rather say that than publish a number nobody has agreed to.
Can I get a refund?
A full refund is due if the tournament is cancelled, or if we take your payment and then cannot admit you. It goes back to the card you paid with, and it is issued by a person rather than automatically. If you entered and simply did not play, the fee is not returned. The refund policy covers every other case.
Fair play
Do you detect cheating?
No, and we do not claim to. The games are played on Lichess, and Lichess’s fair-play systems are what analyse them. What we do is read the account standing Lichess publishes, write down what we read, and refuse to pay a prize to an account Lichess has marked. No automated system here decides that somebody cheated, and no language model is involved anywhere in the process.
What do you actually check, and when?
Your Lichess account standing, at four moments: right after you link the account, periodically in the background while it stays linked, when you take a seat in a tournament, and again before any prize is approved. The last one matters most, because Lichess marks accounts after the fact — sometimes days after a tournament has finished.
Could I be flagged just for playing well?
No. A high rating, a dominant score, a winning streak or an unexpected result against a stronger player produce no flag, no case and no consequence on this platform. Strength is not a signal and we do not treat it as one. If your play is genuinely suspicious that is a judgement for Lichess, who have the games; our record contains no assessment of how you played.
What happens if Lichess is unreachable when you check me?
The check is recorded as inconclusive, which means exactly what it says: we could not read your account, so we know nothing. It is not a finding, it does not open a case, and repeated outages never accumulate into one. The only thing it affects is a prize approval, which needs positive proof rather than an absence of bad news — so we run the check again instead of concluding anything.
Who decides, if something is found?
A person. A case is opened for a named reviewer, who sees every check ever run against the account — including the ones that found nothing — and the facts each was decided on. Closing a case records a decision and a written reason; withholding a prize or restricting an account is a separate deliberate step, so reviewing and punishing can never be the same click.
Can I see what you hold about me?
Yes. Write to us from the address on your account and ask for your fair-play record and the reason behind any decision that affected you. We keep the checks that found nothing too, because “you were checked and nothing was found” is a different statement from “no record exists”.
ChessOS & Share Chess
What is Share Chess?
Our own chessboard, free and open to anyone who opens the page. There are two ways to use it. “Play” puts you against a computer opponent straight away. “Play with a Friend” creates a private arena and gives you a link — send it to somebody, you both press Play, and you are playing each other on separate devices. Neither of you needs an account, an email address or a Lichess login, and nothing is installed. It arrives with ChessOS 3.
Is this the same thing as your tournaments?
No, and the difference matters. Share Chess games are casual. They carry no rating, win no prize, appear on no leaderboard, and have no effect at all on whether you can enter a tournament or what happens if you do. The paid tournaments are a separate product and are still played on Lichess, where your rating and your fair-play standing live. Share Chess is played here, on software we wrote.
Do I really not need an account?
Really. The board opens to anyone, and a friend game asks each player for a display name and nothing else — no address, no password, no verification. The name is used to label the two seats and for nothing else.
How does the link work, and who can use it?
Creating an arena produces one link. The first person who opens it and enters a name takes the second seat; after that the arena is full and anybody else who follows the link is told so. The link is a long random string, so it cannot be guessed, and the page it opens carries no preview text — a chat app that unfurls it learns nothing about the game. We never send it anywhere for you: you decide who gets it.
What happens if I reload, or my connection drops?
You come back to the same seat and the same position. The seat is held by a credential your browser keeps, not by your name, so nobody can take it by typing what you called yourself. A brief disconnection shows your opponent that you are away rather than ending the game. In a timed game the clock keeps running while you are gone, exactly as it would in any other online chess — leaving the table does not stop the clock.
Who decides whether a move is legal, and who keeps the clock?
The server, for both. Your browser asks to move a piece; it never tells us the result. The position, whose turn it is, the clocks and the outcome are all worked out here and sent to both players, so the two boards cannot disagree and neither player can win by changing something on their own machine. It is the same rules engine everywhere in the product — the local board, the computer game and a friend game all use one interpretation of castling, en passant, promotion and a draw.
How strong is the computer?
There are six levels, described by what they actually do rather than by a rating we have not measured. They differ in three ways, not one: how deep the opponent looks, how willing it is to settle for its second-best move, and how often it ignores its own search entirely and plays something else. Learner will hand you pieces. Casual is mostly sensible and then suddenly not. Club takes what is free and sees a mate in one. Sharp punishes a loose piece. Strong always plays what it thinks is best. Relentless does that and also checks every move against the board first, so it will not give you a piece through a gap in its own search. The ordering is measured — the levels were played against each other and each beats the one below it. The engine runs inside your browser, so your game is never sent anywhere and it costs our servers nothing.
Can I change how the board looks?
A lot. Seven boards — Slate, Walnut, Moss, Parchment, Graphite, Ink and a high-contrast pair — and seven sets of figures, each drawn by somebody and credited by name. On top of that: whether legal moves are marked, whether the last move stays highlighted, whether coordinates show, click-to-move or drag, how fast pieces travel or whether they travel at all, and a move and capture sound with its own volume. Six presets set the board, the figures and the marks in one press — and leave your motion, sound and drag preferences alone, because those are about you rather than about how the board looks. It is all under “Board & pieces” on any board. The choice is remembered in your browser and is yours alone: your opponent sees whatever they picked, and neither of you can tell what the other is looking at.
Is there a chat?
No. There is no chat in any mode, and we would rather say that plainly than ship a text box between two anonymous strangers without the part that makes it safe — there is no account to suspend and no report to act on. If we add one, it will be because we have built that part, not because the box was easy.
What is the “with cheats” option I can see but not choose?
An idea we intend to build: a consensual custom-rules mode for private arenas, where two friends agree to play something other than standard chess. None of it exists yet. It is shown in the setup so you can see where this is going, and it is deliberately impossible to select — the server refuses to create a room claiming it, so no arena can promise you rules the software does not have.
How does the move analysis work, and is it sent anywhere?
It runs in your browser, in a background thread, on the same engine the computer opponent uses. Your game is never uploaded for analysis — there is no analysis endpoint on our servers, because there is nothing for one to do. Each move is compared with the best move the engine found in the same position from the same search, and separately checked against the board for material it simply gives away. The engine is small and a few moves deep; it misses some errors rather than inventing them, and the report says so where the number is shown.
Is the score after a game honest, or is it designed to make me feel good?
Honest, and it was changed because it was not. The first version averaged each move’s accuracy in winning chances, which is the usual method — and it scored a game played with entirely random legal moves at 88 out of 100, because once a game is decided winning chances stop moving and further mistakes cost nothing in those terms. The score is now the LOWER of two measures: that accuracy, and ordinary average centipawn loss, which does not saturate. The same random game now scores in the forties. Both figures are shown next to the score so you can check the arithmetic, and a move that demonstrably throws material away is never called your best, whatever the engine thought of it.
What do you keep about a Share Chess game?
If you are NOT signed in: for a computer game, nothing at all — it never leaves your browser. For a friend game we store one row: the invite string, which colour the host plays, the time control, the two display names, the moves, the clock and the result. Seat credentials are stored only as SHA-256 hashes, so a database read cannot impersonate a player. No IP address, no email, no device identifier, no account link. Your board settings live in your own browser’s storage either way, never on our servers.
If you ARE signed in, your finished ChessOS games are recorded against your account so you can have a rating — that is the whole point of signing in here. What we keep is the RESULT, not the game: which opponent, which colour, won or lost or drew, the rating before and after, the points, the number of moves, and this game’s 0–100 score. The moves themselves are sent so the server can check the result is a real game and are not stored. Play signed out and none of that happens.
What is the ChessOS rating, and does it affect tournaments?
It is a strength number for our own chess, and it affects nothing outside it. Signed-in players get one after their first finished game; it goes up when you win and down when you lose, and the dashboard draws how it has moved. It is not a Lichess rating, it is not comparable with one, and it decides nothing about tournament bands, eligibility, entry or prizes — those are settled by your Lichess account and are untouched by it. Alongside it are points, which only ever go up, for turning up and for winning. Two numbers doing two different jobs, and the interface never adds them together. Guests are not rated and nothing about their games is kept.
Can I just make up a result to push my rating up?
Not easily, and not by asking. A computer game runs inside your browser, so the server cannot watch it — which means it does not take the result on trust. The moves are replayed here with the same rules engine the game used: they all have to be legal, and if the position ends in checkmate the winner is read off the board and whatever was claimed is ignored. A win claimed on a game too short to be a game is refused. Two rules also stop the rating being farmed: beating an opponent you were always going to beat is worth nothing, and losing to one you were never going to beat costs nothing — a rating moves on surprises. None of this makes forgery impossible; it makes it no easier than actually playing, which for a free casual mode with no money attached is the right place to stop.
What is ChessOS, and how is it different from Share Chess?
Share Chess is the thing you do — open a board, play a computer or send a friend a link. ChessOS is the software it runs on, and the name we give each version of this site as a whole. When you press play, the website is replaced by ChessOS: no navbar, no footer, no cookie banner, just the board and what belongs to it. The version number is next to the wordmark in the corner of every screen, and “What’s new” on the first setup screen lists what changed, if you want it.
How was ChessOS actually built?
On other people’s work, mostly, and we would rather name it than imply otherwise. The rules of chess are `chess.js`, which decides what is legal everywhere in the product. The computer opponent and the move analysis are `js-chess-engine`, running in a background thread in your browser — we did not write a chess engine, and a product that needs one should not pretend it did. The figures are drawn by artists, each credited by name where you choose them. What is ours is the arrangement: the server that keeps the clock and the position so two browsers cannot disagree, the six opponent strengths built on top of that engine, the judgement that turns its numbers into a sentence you can act on, and everything you can see.
Why does the analysis sometimes disagree with a stronger engine?
Because ours is small and only looks a few moves ahead. It runs in your browser rather than on a server, which is what makes it free, private and instant — and the price of that is a horizon. Where we can prove something without searching we do: a mate in one is checked directly, and material a move gives away is worked out on the board, so a move that hangs a piece is never called your best even when the search liked it. Where we cannot, the report is deliberately reluctant rather than harsh, and it tells you the engine’s limits next to the number rather than in a footnote.
Is ChessOS meant to replace the big chess sites?
No. They have more people, stronger engines, better opening databases and years of work we have not done. What this is for is narrower: a board you can hand somebody without asking them to make an account, and a report afterwards that tells you the truth about how you played rather than a number designed to bring you back. We would rather be honest about a smaller thing than make a claim we would have to defend.
How long does an arena last?
An arena nobody joins is cleared after an hour. A game in progress lasts a day from the last move, and a finished one stays readable for six hours so both players can look at it. After that the room and its moves are deleted outright — not hidden, not archived. The deletion runs on our scheduled job rather than only when the next person happens to start a game, so it does not depend on how busy the site is. Nothing about the arena is kept beyond that. If you were signed in, the RESULT of the game stays on your account for your rating — see the answer above for exactly what that is and what it is not.
Naming and builds
How do I tell which version I am using?
Sign in and open the Control Center from the header; the About panel names the build you are running and can ask the server whether a newer one is deployed. A web page updates by loading again, so that is what it offers — there is nothing to download and no installer.
Why do the versions have names?
Because it is easier to say “that changed in 2.1” than to quote a commit. The name is what a build is called out loud; the build id underneath it is the exact commit the running code was compiled from, and that is the one that settles arguments. The full list of versions and what each one changed is below.
Version history
The history of Chess4Prize and ChessOS. Choose a generation to see its releases, and a release to see what it changed.
ChessOS 6.0
In developmentYou are running this
Team tournaments, a Staff team that works in the open, and a direct line to support.
Play a team tournament from 2 v 2 up to 10 v 10: invite players with a link, guests included, or join a quick tournament among accounts and be matched within ten seconds. Every board is a real ChessOS game, never rated, and leaving a live board has consequences. Support is now a conversation: open Support from the menu, write to the Chess4Prize team and get a reply in the same thread. The public homepage keeps its headline over a centered board playing a complete game; Settings is one searchable workspace, and dashboard announcements and Event Discovery are yours to switch off. Behind the scenes, new Staff members are appointed one account at a time and introduced to their role before their tools open.
Still have a question?
Support replies within one working day. Include your Lichess username if it’s about a specific tournament.