Chess Extensions and Fair Play: What Chess.com and Lichess Allow

Chess extensions are allowed on Chess.com and Lichess as long as they do not help you during a game against another person. Analysis after the game, study on an analysis board and practice against the computer are fine. Any engine suggestion, evaluation or "blunder check" while your game against a human is still running is not, on either site, in rated or unrated games.

That rule applies to every analysis extension, including our own, ChessHelper (chesshelper.ai). ChessHelper's own guidance tells users not to use it in rated games; this page goes through the actual rules so you can see exactly where the line is.

What Chess.com allows

Chess.com's Fair Play Policy is short and specific. Among its rules, it says: "Do not use chess engines, software of any kind, bots, plugins, browser extensions, or any tools that analyze positions during play." It also says: "Do not perform any automated analysis or 'blunder checking' of your games in progress," and "Do not use tablebases or any other resources that show the best move (in both Online and Daily chess)."

There is one explicit allowance: "You may use Opening Explorer or other books in Daily chess only (not in Online / Live play)." Even in Daily chess, engines and tablebases stay off limits; only opening references are permitted.

The policy also states that it does not apply to "games that are not against other users, such as in the game mode versus Chess.com computer (i.e., non-human, virtual) 'bots'." So an analysis extension running while you play a Chess.com bot is outside the fair-play rules. Running it in a live game against a person is inside them, whether the game is rated or not. The policy has no exception for unrated games.

What Lichess allows

Lichess puts its rules in the Terms of Service. It prohibits "the use of any external assistance used whilst a game you are involved in is ongoing." Its examples include using a chess engine, opening books or endgame tablebases, and "receiving move recommendations from another person or software." It adds that certain software or extensions can be treated as a breach at Lichess's discretion.

The one exception: "In correspondence games only, you may use the Lichess opening explorer, plus any other chess books or opening databases." As on Chess.com, engines are not part of that exception.

Lichess is generous with what it offers after a game. Every finished game can be sent to free server analysis, and the analysis board with Stockfish is open to everyone, signed in or not. That is why several popular extensions simply move a finished Chess.com game into the Lichess analysis board.

Over-the-board and federation rules

The same principle runs through official chess. The FIDE Laws of Chess say in Article 11.3.1 that during play "the players are forbidden to use any notes, sources of information or advice, or analyse any game on another chessboard," and Article 11.3.2 bans any electronic device not approved by the arbiter in the playing venue.

US Chess treats outside assistance in rated play as an ethics matter. For online events it has issued formal endorsements of the fair-play methods used by platforms including Chess.com and Lichess, which means a violation on those sites can follow you into rated tournament chess.

Allowed and not allowed at a glance

The table applies the rules above to common ways people use chess extensions.

The last row needs care. A tool like Chess.com Keyboard only changes how you enter moves and gives no advice, so it is not the kind of tool the rules target. Chess.com's wording about "software of any kind" is broad, though, so if you rely on an input tool in live games, a quick question to Chess.com support settles it.

Why "undetectable" is the wrong question

Some extension listings and websites claim their overlay cannot be detected by chess sites. That claim misses how enforcement works. Fair-play teams do not need to see an extension in your browser; they compare how your moves match engine choices, how your accuracy shifts between games, and how long you spend on each move, against large samples of honest play. An account closed for fair play is closed for the moves played, not for the software found.

The practical rule is simpler than any detection debate: if a tool would change a move you play in a game against a person, keep it off.

A fair routine that still uses an extension every day

The rules leave plenty of room for an analysis extension to make you better. A typical routine looks like this:

• Play first, with nothing switched on. Turn off or pause any overlay before you start a game against a person. If an extension runs automatically on chess.com, set its site access to "on click" so it cannot appear mid-game.
• Write down your thoughts. Right after the game, note the two or three moments you were unsure. Your own doubts are the most valuable part of a review.
• Review with the engine. Open the finished game in an analysis tool. Check your noted moments first, then the biggest evaluation swings.
• Turn mistakes into drills. Replay the critical positions against the computer or in a study until the better move feels natural.

An engine pitched at a sensible strength helps here. If you are rated around 1200, a suggestion at roughly 1500 to 1800 shows ideas you can understand and copy, while a full-strength line often relies on tactics that are too deep to learn from. That is the reason we rank adjustable-strength analysis first on our home page.

What happens if you break the rules

Both sites close accounts found using engine assistance, and both say so in their policies. Chess.com closes the account and notes the fair-play violation on the profile, and Lichess marks the account and restricts it. Beyond the platform, a fair-play finding can matter in federation-rated online events that use these platforms' detection. None of that is worth one game.

If you think an opponent used assistance, report the game through the site's report tools. Lichess's terms say public accusations are not tolerated; use the report process instead.

Choosing extensions that respect the rules

When you pick an extension, look at how it is meant to be used. Tools that send finished games to an analysis board, scan positions from videos, or add study features are built around after-game use. Tools marketed for use in live games against people break the rules, and we leave them off our ranked list. Our study picks are all after-game or study tools, and our safety guide explains how to restrict any extension to run only when you click it.

Frequently asked questions