Play Chess Against Nexuron, a Free AI-Built Chess Engine
Promote to
Nexuron search depth
Takes effect from the engine's next move.
Resign this game?
Nexuron takes the win. The moves stay on the board, so you can still review them or send the game to the analyser.
Checkmate
White wins.
How to Play Chess — and Survive Against Nexuron
Nexuron is our own chess engine, and it has an unusual origin story: it was created entirely with AI prompts. Everything below is what you need to sit down against it — how each piece moves, the three moves that look like exceptions, and the habits that keep an engine from taking you apart. The diagrams use the same pieces and board colours as the game above, so whatever theme you have picked here is the one you will see when you play.
Setting up the board
Turn the board so each player has a light square in the near-right corner. The back rank runs rook, knight, bishop, queen, king, bishop, knight, rook — the queen goes on her own colour, which puts the white queen on the light square d1 and the black queen on the dark square d8. Pawns fill the rank in front.
White moves first, then the players alternate, and passing is not allowed: on your turn you must make a legal move. Every piece captures by moving onto an enemy piece's square and taking its place — the pawn is the one exception, and it is covered below.
How the pieces move
The dots on each diagram mark where that piece may go from where it stands. The queen, rook and bishop slide as far as they like along their lines, but they stop at the first piece in the way: they take an enemy piece and are blocked by a friendly one.
King
One square in any direction. He may never step onto a square an enemy piece attacks, and the two kings can never stand side by side. The king is never actually captured — losing him is what ends the game. Against Nexuron: castle early. A king still sitting in the centre on move twelve is exactly the target its search is best at finding.
Queen
Any number of empty squares along a rank, a file or a diagonal — the rook and the bishop rolled into one. She is the strongest piece on the board, worth roughly two rooks. Against Nexuron: do not bring her out early. The engine develops its minor pieces by attacking her, gaining a free move every time she has to run.
Rook
Any number of empty squares in a straight line, along a rank or a file. Rooks come into their own on open files and on the back rank, and they are the only other piece involved in castling. Against Nexuron: it fights hard for open files, and its evaluation pays a bonus for taking one. Connect your rooks and contest them.
Bishop
Any number of empty squares along a diagonal. Each bishop is fixed on the colour it started on for the whole game, which is why a pair of them, covering both colours, is worth so much. Against Nexuron: it scores the bishop pair and rarely misses a discovered attack down a long diagonal. Check the whole line before you commit.
Knight
An L shape: two squares along one line, then one square across. The knight is the only piece that jumps — anything standing in between, friendly or not, simply does not matter. Against Nexuron: forks are what a search engine finds first. Be careful about advanced enemy knights, and trade them off in closed positions.
Pawn
Forward one square, or two if it is still on its starting rank, and never backwards. It is the one piece that captures differently from how it moves: one square diagonally forward, marked here in red. Against Nexuron: its evaluation understands doubled, isolated and passed pawns, so a weak pawn really will be pressured for the rest of the game.
The three special moves
Castling
The king steps two squares towards a rook and that rook hops over to the square on his far side. It is allowed only if neither piece has moved yet, the squares between them are empty, and the king is not in check — nor passing over or landing on a square under attack. It is the one move that tucks the king away and develops a rook at the same time.
En passant
When a pawn uses its two-square move to slip past an enemy pawn, that pawn may take it as though it had only moved one square, landing on the square behind it. The chance lasts for that one reply only, and is gone if you play something else. Nexuron will use it to break a pawn chain, so keep it in mind whenever you push past its pawns.
Promotion
A pawn that reaches the far rank is replaced immediately by a queen, rook, bishop or knight of its own colour. Almost always a queen; a knight now and then, when it comes with check. You are not limited to the pieces you have already lost — and against an engine, one pawn given away carelessly in the opening is often the whole endgame.
How a game ends
Check
The king is under attack and it must be dealt with at once: move him, take the attacker, or block the line. You may never make a move that leaves your own king in check, which is what pins pieces in place.
Checkmate
Check with no legal answer — the game is over on the spot. Here the rook covers the whole eighth rank and the black king is walled in by his own unmoved pawns, a pattern common enough to have a name: the back-rank mate.
Stalemate
Not in check, but no legal move of any kind. That is a draw, not a win. With Black to play here the king is safe where he stands, yet the queen covers all three squares he could go to — so the half point is shared.
A game is drawn in four other ways as well: by agreement between the players, by the same position appearing three times with the same side to move, by fifty moves passing with no capture and no pawn move, or when neither side has enough material to force mate — king and bishop against a lone king, for instance. Games played with a clock add one more: run out of time and you lose, unless your opponent has no way to mate you, in which case it is a draw.
Three principles for surviving the opening
If you want to reach the middlegame without a losing position, these three are worth more than any memorised line:
- Control the centre. The squares e4, d4, e5 and d5 are the high ground. Put pawns on them or aim pieces at them, and Nexuron has less room to work with.
- Develop quickly. Get the knights and bishops off the back rank before you start an attack. An undeveloped piece is a piece the engine gets to ignore.
- Protect the king. Castle by move ten if you can. A centralised king is the single thing a search engine punishes most reliably.
Reading the move list
Moves are written in algebraic notation, the same form the move list beside the board uses and the same form you get from Copy PGN. A move names the piece and the square it lands on — and a pawn move names only the square.
About Nexuron
Nexuron was created entirely with AI prompts. Every part of it — the board representation, the move generator, the search, the evaluation and even this page — was written by an AI model responding to plain-English instructions, then tested and refined the same way. No hand-written engine code, no borrowed engine libraries. It is a working demonstration of how far prompt-driven software development has come.
Unlike most online chess engines, Nexuron does not run on a server. The whole engine is downloaded to your browser and thinks inside a Web Worker on your own device, which is why its difficulty control is a search depth slider rather than a strength setting: you decide how many moves ahead it is allowed to look, trading your computer's time for playing strength.
How Nexuron thinks
It searches a tree of possible futures: alpha–beta with iterative deepening, looking one move ahead, then two, then three, reusing what it learned each time. Around that core sit a transposition table that remembers a million judged positions, null-move pruning and late-move reductions, killer-move and history heuristics, and a quiescence search that keeps calculating through captures so it never stops in the middle of a trade.
How it judges a position
Material is the starting point, but every piece is also judged by where it stands, using paired middlegame and endgame piece-square tables that blend as pieces leave the board — so the king hides in the corner early and marches to the centre late. On top of that it understands doubled, isolated and passed pawns, rooks on open files, the bishop pair, and the pawn shield in front of a castled king.
What the depth slider does
Depth is how many moves ahead it looks before pruning. At 1 to 3 it sees immediate captures and one-move threats — a fair opponent for a beginner. At 6 to 8 it finds multi-move tactics and punishes most club-level mistakes, usually inside a second or two. At 10 to 12 it plays a genuinely strong game, though sharp positions take longer on a slower device.
How strong is it?
Honestly: Nexuron will not threaten Stockfish, which has had two decades of world-class engineering behind it. But at full depth it plays a solid, tactical game at strong club level — more than enough to beat most human players — with code conjured entirely out of AI prompts. To measure yourself against the strongest engine on earth, play Stockfish instead.
Whichever depth you pick, the engine carries a hard thinking cap, so it can never freeze your browser tab. And because it runs on your device rather than ours, nothing about your game is ever sent anywhere: the position, the moves and the analysis all stay with you.
Nexuron is one of several ways to play chess against AI here: pit the big language models against each other in the AI Chess Arena, get every move graded live by an AI chess coach, sharpen your tactics with chess puzzles, or play rated-style games to estimate your ELO with Stockfish.
Nexuron FAQ
Is Nexuron free to play?
Yes. Nexuron runs entirely in your browser, so there is no account, no queue and no limit on games.
How strong is Nexuron?
At depth 1–3 it plays like a beginner; at 6–8 it punishes club-level mistakes; at 10–12 it plays a strong club-level game. It is far weaker than Stockfish, which is rather the point — it is beatable.
Does Nexuron upload my games?
No. The engine thinks in a Web Worker on your own device; your moves never leave your browser.