THE COACH'S EYE
What the coach
actually sees.
The One Chess coach is not a chat bot guessing at your game. It is a chess engine wrapped in a strict rule: never say anything it cannot prove on the board. Every tactic it names is checked by playing out the captures. Every threat it warns about is a move the engine actually found. When it cannot prove something, it stays quiet. This page lists everything it can see, in plain chess language.
Graded by winning chances,
not pawn counts.
Engines score positions in pawns, but a two-pawn slip means nothing when you are up a queen and everything in an equal endgame. So the coach converts every evaluation into a winning percentage and grades each move by how much of your winning chance it gave away.
| Grade | What it means | How it is earned |
|---|---|---|
| Brilliant | The engine's move — and it took nerve | You found the best move, and it was a real sacrifice (the piece can genuinely be taken) or the only move that didn't lose ground. |
| Great | The engine's move | You matched the engine's first choice with essentially nothing given away. |
| Good | Kept your chances | A small, harmless concession — the game's story did not change. |
| Inaccuracy | A real concession | You handed back a noticeable slice of your winning chances. |
| Mistake | The game changed | A winning position became equal, or an equal one became worse. |
| Blunder | The game turned | A large share of your winning chances gone in one move — and the coach will show you exactly why. |
"Brilliant" cannot be earned by a quiet recapture. The coach checks that the move really hangs material the opponent could take, or that every alternative lost — the same bar a human annotator would set.
Not just "that was a blunder."
The refutation, and what it wins.
A grade without a reason teaches nothing. After a bad move the coach reconstructs the punishment and names it.
THE REFUTATION
The exact reply that punishes you
Not "this loses material" but "…Rxd1 wins the queen" or "…Re1 delivers a back-rank mate." The coach plays the opponent's strongest answer and reports what it achieves: checkmate, a winning capture, or a new fork, pin, or skewer that didn't exist before your move.
THE THREAT RADAR
What the opponent is threatening — and whose fault it is
The coach asks the engine a classic coach's question: "if you could pass, what would your opponent do to you?" The answer is the live threat in the position. Crucially, it distinguishes threats your last move allowed from threats that were already hanging over the position — so you know whether you created the problem or merely failed to solve it.
THE MISSED PLAN
What you should have played, as an idea
Instead of a bare move, the coach names the idea: "push the passed pawn," "centralize the knight," "castle," "recapture," "win the queen — it was undefended." When the engine's choice was a quiet move, the coach checks whether it prevented an opponent threat, and tells you so: prophylaxis, explained.
MOVE CRITICALITY
It knows when a position was forcing — and when it wasn't
By comparing the engine's top choices against each other, the coach knows whether the position had one only move, a critical choice, or many roads to the same place. If six moves were all fine, it will not scold you for missing the "best" one.
Before it says "hanging,"
it counts the captures.
Most "hanging piece" warnings in chess apps are wrong, because a defended piece is not hanging. The One Chess coach settles every material claim the way a strong player does at the board.
RULE 1
Play out the whole exchange, cheapest piece first
Pawn takes before knight, knight before rook, rook before queen — and either side may stop recapturing the moment continuing loses material. Only if the full sequence wins material does the coach call the piece hanging.
RULE 2
Pinned defenders don't count
A bishop pinned to its king cannot recapture, and the coach knows it. Pieces that are absolutely pinned are excluded from the exchange — unless the capture happens along the very line of the pin.
RULE 3
Pieces hiding behind the attackers join in
Doubled rooks, a queen behind a bishop: when the front piece captures, the one behind it enters the fight. The count includes these discovered attackers and defenders — the detail most quick "hanging piece" checks miss.
This one capture-counting test sits underneath nearly everything else on this page. Forks, skewers, overloads, "remove the defender" — every material claim the coach makes has been played out, not eyeballed.
Every motif, with the proof
it demands before speaking.
The coach sees tactics for both sides — yours in blue, your opponent's in red. Each one must pass its own truth test.
VERIFIED, THEN SHOWN
Both prongs drawn, only when the fork is real
Before drawing those arrows the coach checks the forking piece: is it safe on its square, or winning more than it costs? Is it pinned? Does the opponent have one reply that defuses both threats at once — a capture, or a move that saves one piece while defending the other?
THE FAKE FORK STAYS HIDDEN
A knight that forks two pieces but stands en prise to a pawn is not a fork
It is a blunder waiting to happen — and the coach refuses to decorate it. This single filter removes most of the false "tactics!" noise other tools produce.
HANGING PIECE
Loose material
A piece that loses material to the full capture count above — not merely "attacked."
FORK
Two targets, one piece
The forking piece must be safe on its square (or win more than it costs), must not be pinned, and must survive the opponent's best single defensive reply. A royal fork — check included — passes regardless: the king must move.
PIN & SKEWER
Pieces on a line
A skewer only counts if the front piece is genuinely forced off the line — if it can simply capture the skewering piece for profit, there is no skewer. Pins to the king are absolute and feed every other check the coach runs.
DISCOVERED & DOUBLE CHECK
The uncovered attack
Moving one piece to unveil another — discovered attacks on heavy pieces, discovered checks, and the double check, which the coach names with respect: it cannot be blocked, only escaped.
TRAPPED PIECE
No safe squares
A piece whose every escape square is covered — detected for both armies, including your opponent's queen wandering into a net.
OVERLOADING & DEFLECTION
The overworked defender
A defender is overloaded only if it is the sole guard of two or more points that genuinely fall when it is removed — proven by lifting it off the board and re-counting the captures at each duty.
REMOVE THE DEFENDER
Capture the guard, win the charge
When the engine's best move captures a piece, the coach checks what that piece was holding together — and tells you which target falls once the defender is gone.
DECOY
The poisoned offer
Named only when the lure is a real sacrifice — material genuinely offered so that taking it walks into a bigger blow. An even trade is not a decoy.
ZWISCHENZUG
The in-between move
When the engine's line delays an obvious recapture to throw in a check or a bigger capture first — and still collects the recapture later — the coach points out the in-between move you missed.
X-RAY & BATTERY
Pressure through a piece
A rook bearing through a pawn, a queen stacked behind a bishop. Mentioned only when the engine's best move actually uses that line — otherwise it is wallpaper, and the coach stays quiet.
MATE THREATS
Forced mate on the horizon
Mate-in-N threats from the engine's own line, for either side — never from pattern guesswork.
NAMED MATES
The classics, by name
Back-rank mate (king boxed in by its own pawns), smothered mate (a knight, and the king buried by its own army), and the Greek gift — the bishop sacrifice on h7 with knight and queen storming in behind.
The quiet judgments
between the tactics.
When nothing is hanging, a coach should still have something true to say. These positional readings are held to the same standard: each one has strict conditions, so they appear when they matter and stay silent when they don't.
KING SAFETY
Danger that is real
"Your king is exposed" only when the opponent still has the firepower to exploit it — roughly a queen plus a piece, or two rooks. A bare king in a pawn endgame is not in danger, and the coach knows it.
BACK RANK
The classic trap
Flagged only when all three conditions hold: no escape square for the king, an enemy rook or queen with a real road to your back rank, and no defender of your own already covering it.
ATTACK COUNT
Attackers vs defenders at the king
The coach counts pieces bearing on each king's neighborhood. When attackers clearly outnumber defenders, it says whose attack is brewing — yours or theirs.
PAWN STRUCTURE
Passers, doubled pawns, holes
Passed pawns with their status — blockaded, path contested, or free to run. Doubled pawns named once per pair. Holes in either camp that no pawn can ever again defend.
COLOR COMPLEX
Weak squares of one color
When the squares of one color around your king can never be defended by your pawns and you no longer own the bishop of that color, the coach names the weakness — the classic fianchetto hole after the bishop is traded.
GOOD & BAD BISHOPS
The bishop pair, and the prisoner
It tells you when you own the two bishops and should open the position — and when your last bishop is buried behind four of its own fixed pawns, French-defense style.
ROOK PLACEMENT
Open files and the 7th rank
Rooks on open and half-open files, and rooks on the 7th — but only when the 7th actually pays: an enemy king boxed on the back ranks or pawns there to harvest.
WORST PIECE
"Improve your worst piece"
The oldest advice in chess, made concrete: the coach finds your least active piece by counting the squares it actually influences, and names it — "the a1-rook."
DEVELOPMENT
Tempo accounting
In the opening it counts developed pieces and castling for both sides. Fall two tempi behind and it will tell you to stop grabbing pawns and get your pieces out.
COMPENSATION
When material lies
Down a piece but the engine likes you? "Down material with full compensation — keep the initiative." Up material but worse? It warns you the extra pawn is not the whole story.
TRADE ADVICE
When to swap, when to keep
"Trade pieces when ahead, avoid trades when worse" — spoken only at an actual trading decision, never as a nagging banner.
OUTPOSTS & SPACE
Squares worth owning
Knight outposts on protected squares in the opponent's half — a knight on your own second rank is not an "outpost" — plus the space edge and where it comes from.
Textbook endings,
called by the book.
In simplified positions the coach switches from tactician to technician and teaches the classical rules at the exact moment they decide the game.
THE OPPOSITION
Who really has it
Kings facing off with one square between them, in a pure pawn ending: the side not to move holds the opposition, and the coach says so — direct or diagonal.
KEY SQUARES
King and pawn vs king, solved
For the classic K+P vs K ending it knows the key-square table: get your king to one of the three squares in front of the pawn and the win is yours regardless of the opposition. It highlights them on the board.
THE RULE OF THE SQUARE
Can the king catch the passer?
For every passed pawn in a pawn race, the coach runs the square count — including whose move it is and the pawn's double-step from its home rank — and tells you straight: "the king catches it" or "it promotes — run it."
THE WRONG BISHOP
The fortress it refuses to celebrate
Rook's pawn plus the bishop that doesn't control the promotion corner, defending king in the corner: a known draw, no matter what the evaluation bar says. The coach caps its own enthusiasm — no "you're winning!" in a position the books call drawn — and tells you the one thing that matters: keep the defending king out of that corner.
ROOKS BEHIND PASSERS
Tarrasch's rule, applied
In rook endings with a passed pawn it checks every rook on the pawn's file: behind the passer is the ideal — yours or the opponent's — and in front of it is a rook that needs to move.
One grammar on the board.
Color is meaning.
Everything the coach sees is drawn with a fixed visual language — arrows for moves and relations, rings for squares and pieces. Learn it once, read it everywhere.
| Mark | Meaning |
|---|---|
| Green | The engine's move — shown only when you've asked for answers, never during your think. |
| Red | Danger to you: a hanging piece, the refutation arrow, the opponent's live threat. |
| Yellow | King safety caution — weak squares and gathering attackers. |
| Blue | Your chances: tactics you have, files your rooks own, pawns that can run. |
| Gray | Insight — quieter ideas like "improve your worst piece." |
| Solid vs dashed | A solid mark is something your last move created. A dashed mark was already in the position before you moved. |
DISCIPLINE 1
At most three marks per color
When more than three things compete, the biggest wins are kept — a queen fork outranks a pawn fork — and the rest stay off the board.
DISCIPLINE 2
One story at a time
If a piece is hanging, the board shows the tactic and nothing else. Positional niceties wait their turn — the board never tells five stories at once.
DISCIPLINE 3
Every mark is a sentence
In review, each mark appears as a plain-language line — "Your fork hits d8," "Passed pawn on b5 — it promotes: run it." Tap the line and the board isolates that mark.
A coach you can trust
is mostly a coach that shuts up.
RULE
No false optimism
When you are losing badly, "you have a chance!" cues are suppressed. You get the threats against you and the best defense — not cheerleading.
RULE
No applause for a bad move
If your move made things worse, the coach will not celebrate the winning position you still happen to have. And in known fortress draws, it refuses to call "winning" at all.
RULE
Both sides, same eyes
Every detector runs for you and your opponent alike. Your trapped piece and theirs, your back-rank and theirs — the coach has no favorite.
RULE
No spoilers while you think
During your move, the coach can warn without revealing: it will tell you a reply punishes your idea without naming the move, and holds the answers until you ask.
RULE
Proven, or unsaid
Anything that fails its truth test — a fork that loses the forking piece, an "x-ray" the engine ignores, a skewer the queen can just eat — is never shown. Silence over speculation, every time.
Your blunders become
your curriculum.
Every mistake the coach catches is filed under the tactical theme it belongs to — fork, pin, back-rank mate, removal of the defender — and feeds the spaced-repetition review queue. You don't just hear what went wrong; you drill that exact pattern until it stops happening.