Using a chess engine is cheating when you consult it during a game against another person. Chess.com, Lichess and FIDE all forbid it, and the penalty ranges from a closed account to a lost game. Using an engine after the game, to study, to solve puzzles or to play against the engine itself is not cheating, because no opponent is being deceived.
The test is simple: is a game you are playing still in progress, and is the other side a human who expects you to play alone? If yes, the engine stays closed. Every rule below is a version of that sentence.
What Chess.com's fair play rules say
Chess.com's Fair Play Policy tells players: "Do not use chess engines, software of any kind, bots, plugins, browser extensions," or "any tools that analyze positions during play." It also bans tablebases or "any other resources that show the best move", help from any other person ("including parents, friends, coaches, or other players"), and automated analysis or "blunder checking" of games in progress.
The help centre article What counts as cheating on Chess.com splits the rules by game type:
- Live games (bullet, blitz, rapid), Puzzle Rush and rated tactics: "You may not use any engines to analyze ongoing games," and "you should not look at anything other than the game in front of you."
- Daily games: you may consult "chess books, lessons, or videos," use opening databases that do not use an engine to evaluate moves, and use the self-analysis board to explore moves yourself. Engines and tablebases are still banned.
- The exceptions: "Unrated puzzles and games against computer personalities are the only exceptions to the rules above," where "you are free to experiment with any tools."
Note the wording: every ban is about ongoing games. Nothing in either page restricts studying a game once it is over.
What Lichess's fair play rules say
Lichess's fair play page is shorter and just as firm: "We prohibit the use of any external assistance used whilst a game you are involved in is ongoing," and "examples of cheating include, but are not limited to, using a chess engine."
Lichess lists where engines are and are not permitted:
- Not permitted: real-time games (rated or casual), correspondence games, games against Lichess Bot accounts, and games played through the Board API.
- Permitted: games against the Lichess AI and games played through the Bot API, which is the interface for running an engine as an openly declared bot account.
- Correspondence extra: "In correspondence games only, you may use the Lichess opening explorer, plus any other chess books or opening databases." Engines are not on that list.
So a slow correspondence game on Lichess gives you more time and lets you open books, but not Stockfish.
FIDE's rule on electronic devices over the board
In tournament chess the rule is about the device itself, not only about using it. Article 11.3.2 of the FIDE Laws of Chess says "a player is forbidden to have any electronic device not specifically approved by the arbiter in the playing venue." Article 11.3.2.2 sets the penalty: "If it is evident that a player has such a device on their person in the playing venue, the player shall lose the game," and the opponent wins. The same article lets an event's regulations specify "a different, less severe, penalty", which is why some events handle a ringing phone in the bag differently.
The practical meaning is stricter than "don't use an engine". At a FIDE-rated event, a phone in your pocket can cost you the game even if you never looked at it. Leave it where the arbiter tells you to.
Correspondence chess: the one place engines are part of the game
Correspondence chess under the International Correspondence Chess Federation (ICCF) is the main exception. According to the Wikipedia article on correspondence chess, which cites a 2022 New York Times report, the ICCF "allows for collaboration between humans and computers, even during the World Correspondence Chess Championship", a "hybrid competition that involves the strategy and planning of humans guided by the accuracy of machines."
Two caveats. First, this is the ICCF's rule, not a general correspondence rule: as Chess.com's own correspondence chess page puts it, "Each correspondence organization has different rules for engine usage," and on Chess.com "you are not allowed to use engines in any capacity." Lichess correspondence bans them too. Second, the ICCF's Code of Conduct still says "players will decide the moves for themselves" and that it is "unacceptable behaviour to have someone else play your games." Engines are tools you direct; another person playing for you is not allowed.
Allowed vs not allowed: the quick reference
| Activity | Allowed? | Source |
|---|---|---|
| Engine during a live game against a person (Chess.com) | No | Chess.com Fair Play Policy |
| Engine during a Daily (correspondence) game on Chess.com | No; books, videos and non-engine opening databases are allowed | Chess.com help centre |
| Tablebases during a game on Chess.com | No | Chess.com help centre |
| Any tool in unrated puzzles or games against Chess.com computer personalities | Yes | Chess.com help centre |
| Engine during a real-time or correspondence game on Lichess | No | Lichess fair play |
| Opening explorer and books in Lichess correspondence | Yes | Lichess fair play |
| Playing against the Lichess AI, or as a declared Bot API account | Yes | Lichess fair play |
| Carrying an unapproved phone or device in a FIDE playing venue | No; the default penalty is loss of the game | FIDE Laws, Art. 11.3.2 |
| Engine assistance in ICCF correspondence chess | Yes | Wikipedia, citing the NYT |
| Analysing your own finished games with an engine | Yes; the bans above cover only games in progress | Chess.com, Lichess |
If an activity is not in the table, apply the test from the top: a game you are still playing, against a person, means no engine.
How sites detect engine use
Chess.com describes its system only in broad terms, and deliberately so. Its fair play overview says it uses "a continuously evolving algorithm to review millions of games every day" that "detects suspicious play based on over 100 gameplay factors." Unclear cases and player reports go to human analysts, and cases involving titled players go to a panel that reviews the games by hand. It also says "we look closely at the level of play, but we also consider multiple behavioral factors," and it does not publish its specific methods because that would help cheaters.
Lichess's fair play page does not describe its detection methods at all. Both sites ask players to report suspected cheating rather than accuse opponents publicly.
The takeaway is not how to slip past these systems; it is that the risk is lopsided. You might gain a few rating points, and you put your account and every game on it at stake.
How to use an engine to get better, legitimately
An engine is the best coach most players will ever have, as long as you use it after the game. A routine that works:
- Play the game alone. No engine, no tablebase, no second screen.
- Write down your thoughts first. Before opening any engine, mark the moments you were unsure. This is the part that actually trains your thinking; our guide on how to analyze a chess game walks through it.
- Run a review. Paste the PGN into Game Review to find the moves where the evaluation swung, then open the critical positions in the analysis board and test your own ideas against the engine's.
- Ask why, not just what. The engine's best move is only useful if you can explain it. If you cannot, play the line out move by move until you can.
- Turn mistakes into drills. If you keep missing the same pattern, train it in puzzles, where tools are allowed and the feedback is instant.
You can also simply play the engine. A game against a computer opponent in our play chess tool deceives no one, and it is the quickest way to practise an opening or an endgame you just studied.
Chess Move Finder is built for this kind of study, never for live games against people; the about page explains what the tools do.
Frequently asked questions
Is it cheating to analyze a game with an engine after it's finished?
No. Chess.com's and Lichess's bans apply to games that are ongoing. Once the game is over, engine analysis is ordinary study, and it is how most players review their mistakes.
Is using an engine in Chess.com Daily games allowed?
No. Chess.com allows books, lessons, videos, non-engine opening databases and its self-analysis board in Daily games, but engines and tablebases are banned there just as in Live games.
Is using an engine in correspondence chess cheating?
It depends on the organiser. Engines are banned in correspondence games on Chess.com and Lichess, while the ICCF allows human-computer collaboration, including in its World Championship. Read the rules of the specific event.
Is it cheating to use an opening book during a game?
In real-time games, yes on both major sites. In Chess.com Daily games and Lichess correspondence games, opening books and databases are allowed, as long as they do not use an engine to rank the moves.
Can I have my phone with me at a chess tournament?
Not on you in the playing venue unless the arbiter approves it. Under FIDE Article 11.3.2.2 the default penalty for carrying an unapproved device is losing the game, though an event's rules may set a lighter penalty.