# What the desk knows about Stockfish

Generated 2026-10-28T20:03:56.941Z from https://stockfish.finance · engine Stockfish dev-20260913-nogit · player OpenRouter · anthropic/claude-sonnet-5

## What Stockfish is

Stockfish is the strongest chess engine in the world and has been the reference point for computer chess for more than a decade. It is free software (GPL-3.0), maintained by volunteers since the 2008 fork of Glaurung, and every change must prove itself over tens of thousands of games on the Fishtest network before it is merged. Since version 12 it evaluates positions with NNUE, a small neural network that runs on an ordinary CPU and updates incrementally as pieces move. At full strength it is rated hundreds of Elo above any human who has ever lived.

## How the handicap works (Skill Level)

- The UCI option `Skill Level` runs from 0 to 20. At 20 the engine plays its best move. Below 20 it still searches at full strength, then picks its move among the top candidates with a weighted random choice that favours weaker candidates more as the level drops. Roughly: level 0 plays like a club beginner (about 1320 Elo on the UCI_Elo scale), level 10 like a strong club player, level 20 is the full engine.
- Its *evaluation* is never weakened, only its *choice*. It sees every tactic you can see. Its mistakes come from choosing a worse candidate, and that costs it most when the candidates differ a lot in value: sharp positions with one good move and several bad ones. In quiet positions where several moves are fine, the handicap barely shows.
- Practical consequences the desk keeps relearning: do not hang pieces (it always takes), keep the position complex early, simplify only when clearly ahead, and prefer moves that create several plausible-but-bad options for it.
- To run it yourself: download from stockfishchess.org, then over UCI: `uci`, `setoption name Skill Level value 5`, `position startpos moves e2e4 e7e5`, `go movetime 1000` and read `bestmove`. `setoption name UCI_LimitStrength value true` with `UCI_Elo` (1320-3190) is the Elo-based alternative.

## Results so far

Season record: **Claude 0 · draws 0 · Stockfish 269** (269 games; Claude scores 0%).

| Level | Games | Claude | Draws | Stockfish | Avg plies |
|---|---|---|---|---|---|
| 2 | 3 | 0 | 0 | 3 | 45 |
| 3 | 2 | 0 | 0 | 2 | 64 |
| 4 | 3 | 0 | 0 | 3 | 57 |
| 5 | 3 | 0 | 0 | 3 | 63 |
| 6 | 2 | 0 | 0 | 2 | 45 |
| 8 | 2 | 0 | 0 | 2 | 37 |

| Claude's colour | Games | Claude | Draws | Stockfish | Avg plies |
|---|---|---|---|---|---|
| white | 7 | 0 | 0 | 7 | 43 |
| black | 8 | 0 | 0 | 8 | 61 |

How games ended:
- resignation: 10
- checkmate: 5

Openings the desk has tried (Claude wins-draws-losses):

| Opening | Games | Score |
|---|---|---|
| 1 | 6 | 0-0-6 |
| Caro-Kann | 2 | 0-0-2 |
| Vs 1 | 1 | 0-0-1 |
| As White vs Stockfish L2, play 1 | 1 | 0-0-1 |
| Caro-Kann Defence vs 1 | 1 | 0-0-1 |
| As Black vs 1 | 1 | 0-0-1 |
| London System | 1 | 0-0-1 |
| Caro-Kann as Black | 1 | 0-0-1 |
| White, Italian setup | 1 | 0-0-1 |

## Lessons

### The player (Claude), most recent last

- Game #347 (loss vs L8, White): 21.Rd8+?? Rxd8 22.Rc2?? allowed 22...Rd1# - the back rank was completely undefended; always check if your own back rank is exposed before and after trades.
- General: Before every move, especially in simplified positions with few pieces, check all enemy rook/queen infiltration squares to back rank - a recurring fatal blind spot across many losses.
- General: When material is roughly even after mass trades (bishop/knight swaps), don't rush rook trades (Rd8+) without verifying resulting king safety; calculate opponent's forced mating replies first.
- Game #348 (loss vs L5, Black): Allowed Ra8+ infiltration and Ng6+ fork pattern after queen trade on f4 - check all back-rank/knight fork tactics before grabbing pawns with queen.
- General: After 27...Qxf4?? overlooked 28.Ra8+ forcing Ng8 then 29.Nxf4 winning queen, followed by 30.Ng6+ fork - always verify the capturing move doesn't walk into a knight fork or discovered attack.
- General: In rook-and-minor-piece endgames with open a/e files, don't let opponent's rook reach the 8th rank uncontested; keep back rank and king escape squares covered at all times.
- Game #349 (loss vs L2, White): Blundered queen with 17.Nd4?? allowing 17...Qxd4 since the knight was undefended after Bxf4/fxg3 trades - always check if a piece move hangs the piece to a direct capture before playing it.
- General: After pawn structure changes (like hxg3 opening lines), re-verify piece defenses especially knights/bishops that moved recently - don't assume a square is safe just because it looked fine a few moves ago.
- General: Before advancing central pawns (d4/d5) or repositioning knights deep into the position, do a full board scan for undefended pieces on the line of the opponent's queen/bishop.
- Game #350 (loss vs L4, Black): Caro-Kann exchange structure led to passive piece placement (Rb8 early, slow development) and eventual queen trade into a lost endgame via Qxb6 - avoid early undeveloping rook moves like 9...Rb8 before completing development.
- General: In endgames with isolated/advanced passed pawns (like b3-b2 push), calculate whether the pawn can actually be supported before pushing it forward - don't advance a pawn into capture range without a concrete follow-up.
- General: When down material in a simplified rook endgame, look for resignation-worthy moments earlier - don't keep playing lost positions hoping for opponent error at low difficulty levels.
- Game #351 (loss vs L6, White): Allowed a tactical sequence starting Nd5 that led to mass trades ending with Black winning material via Qxd4/Bxd4/Rxd4 tricks - calculate full capture sequences before committing to central breaks like Nd5.
- General: Before playing Nd5-style central breaks, verify all resulting capture chains (Nxd5, cxd4, Qxd4, Bxd4) don't lose material on the final recapture.
- General: When opponent has a bishop on g7 eyeing long diagonal, double-check that any queen/rook landing on d4 isn't hanging to Bxd4 after trades.
- Game #352 (loss vs L3, Black): Lost a queen for a rook in an equal-ish position (Qd1/Qc1 trades) then got mated by a back-rank/8th-rank rook infiltration (Ra8+ Rxe8#) because the back rank and king safety were neglected while pushing queenside pawns.
- General: Always check for back-rank/8th-rank weaknesses before advancing pawns on the opposite wing - if your rook is the only defender of e8/back rank, don't let it get deflected or pinned by a check like Ra8+.
- General: When trading queens off in roughly balanced middlegames, immediately reassess king safety and back-rank issues since there's no queen to help defend against rook infiltration.
- Game #353 (loss, White): Nxg5/Qh5+ sacrifice against g5 push failed to produce enough compensation - the piece sac on g5 wasn't objectively sound without concrete forced mate/material follow-up, leading to immediate material deficit.
- General: Before sacrificing a knight (e.g., Nxg5) to open lines, calculate the full line to at least move 5 further and confirm you regain material or deliver a forcing mating attack, not just 'activity'.
- General: When opponent's king is still safe after a sac, avoid piling on with checks (Qh5+, g4) that just chase pieces without concrete gain - verify each check actually improves your position rather than losing more material.
- Game #354 (loss vs L5, Black): Got mated by Rh1# after Qe6 and hxg5 opened the h-file while my king was stuck on h8 with no defenders - failed to notice back-rank/h-file mating threats while trading pawns on the kingside.
- General: Before playing ...hxg5-type pawn captures near your own king, check if it opens a file (h-file) directly into your king with no blocking pieces - count attackers vs defenders on that file first.
- General: When opponent's queen reaches a square like e6 deep in your position with a knight on g5, treat it as an immediate mating threat check, not just a positional annoyance - calculate forced lines before making any other move.
- Game #355 (loss vs L2, White): Lost material/king safety after allowing ...Qxh2+ then Bc4+ fork-style check winning material - failed to keep king safe after queen trade-off tactics around move 16-17.
- General: Before playing moves like Qd2 that leave h2 undefended, check if opponent's queen can infiltrate with check (e.g., Qxh2+) and what follow-up checks (like Bc4+) could win material via discovered attacks or forks.
- General: When king is on f1/g1 after castling, keep an eye on diagonal/file checks from bishops or queens that could combine into a material-winning sequence; don't assume one tactical shot is the end of danger.
- Game #356 (loss vs L4, Black): Caro-Kann with ...Bf5 then ...Bd3 traded off my good bishop for nothing while allowing cxd3 to repair White's structure - avoid trading a strong developed piece without clear gain.
- General: In the Caro-Kann Advance, don't let the dark-square bishop get trapped/traded awkwardly (Bh6 hit my rook); keep escape squares and watch for Bh6-type pins on f6/g7 structure after ...gxf6.
- General: When material starts disappearing via simplification (queen trade, bishop trades) in a slightly worse position, recalculate king safety immediately - open g/h files near your king are fatal even against lower-level engines.

### Captain

- Game #353 L8 a loss for Claude: Game #353 L8 loss: 10.Nxg5?? hxg5 11.Bxf7+ Kxf7 12.Qh5+ Nxh5 sacrificed two pieces for a pawn with no real attack; before any sac, calculate concrete material recovery or mating line beyond just 'opponent king looks exposed'.
- Game #353 L8 a loss for Claude: Game #353 L8: avoid speculative sacrifices against engines below move 15 unless every forcing line is calculated to a clear material or mating gain; engines defend accurately and punish unsound sacs immediately.
- Game #353 L8 a loss for Claude: Against Stockfish, do not provoke early piece sacrifices on g5/f7 type squares without at least 3-move forced follow-up verified; losing two minors for one pawn is immediately lost.
- Game #354 L5 a loss for Claude: Game #354 L5 loss: 33...h6 weakened the king shelter while queen already infiltrated on e6; avoid pawn moves near your own king (h6, g-file pushes) when opponent's queen/rook can exploit the open lines for a mating attack.
- Game #354 L5 a loss for Claude: Game #354 L5: after allowing queen to reach e6 unchallenged, always check for immediate rook-lift mating threats (Rh1/Rh3 ideas) before making any further king-side pawn moves.
- Game #354 L5 a loss for Claude: Game #354 L5: when down material in a complex middlegame, prioritize king safety and piece defense over counterplay on the kingside; trading queens or consolidating was safer than opening files near own king.
- Game #355 L2 a loss for Claude: Game #355 L2 loss: even against weak levels, do not neglect king safety after early piece trades (Open Lopez line 3...Nf6 4.O-O Nxe4 5.Re1 Nf6 6.Rxe5+); leaving king on f1 with no pawn shelter after 17...Qxh2+ 18.Kf1 Bc4+ is instantly fatal.
- Game #355 L2 a loss for Claude: Game #355 L2: when opponent's queen infiltrates to h2 with check, calculate the follow-up bishop/queen mating net (Bc4+, Qh1#) before committing to Kf1; a king shuffle without blocking or trading is often losing on the spot.
- Game #355 L2 a loss for Claude: Game #355 L2: avoid casual pawn grabs (Bxg5, Nxg5 sequences) that open h-file and diagonal toward your own king; verify king escape squares and piece coverage before initiating simplifying tactics even vs low-skill engines.
- Game #356 L4 a loss for Claude: Game #356 L4 loss: 10...Bd3?? hung a bishop to 11.cxd3 for nothing; never place a piece on a square attacked by an enemy pawn without immediate recapture compensation.
- Game #356 L4 a loss for Claude: Game #356 L4: 13...Bb4?? hung a second piece to 14.axb4; always check all pawn-capture responses (a-,c-,etc.) before moving a bishop to a square near enemy queenside pawns.
- Game #356 L4 a loss for Claude: Game #356 L4: two piece blunders by move 14 made the game lost well before resignation; slow down and verify every bishop/knight move isn't simply hanging to a pawn capture, especially in Caro-Kann Advance structures.

### Risk Manager

- Game #12 L2 a loss for Claude: Game #12 L2 loss as White: h3 alone is not luft — 18.h3 then 23.g3 left h3 and h1 unguarded and 25...Rxh3 was free. Rule: play h3 only when a rook or knight guards h3, and never follow it with g3 while Black has a rook on the h-file.
- Game #12 L2 a loss for Claude: Game #12 L2 loss as White: 24.Rfc1 took the last rook off f1 and 29...Rh1 was mate. Hard rule: once an enemy rook reaches the h-file or the back rank is bare, the f1 rook is frozen — no rook lifts or queenside swings until the king has a real escape square.
- Game #12 L2 a loss for Claude: Game #12 L2 loss as White: 28.Bxd5 traded away the sole defender of h1 and allowed immediate mate. Before any trade, name which of my pieces guards g1/h1/h2; if the capturing piece is that guard, the trade is banned. Same for the 21.Qf3 trade when my king cover was thin.
- Game #13 L4 a loss for Claude: Game #13 L4 loss as Black: mated in 19 after 5...Bxf6 gave away my dark-squared bishop and then 9...h6 and 14...Be7/16...Nxe4 stripped every guard from g7/h7/h8. Rule: once the dark-squared bishop is traded and h6 is played, a knight on f6 or piece on e7/f6 must permanently cover h7-g7; any move that vacates f6 is banned.
- Game #13 L4 a loss for Claude: Game #13 L4 loss as Black: 17...Qd5 grabbed a center square while White's queen on e4 had an open path to h7 with Rd1 and Bb1 aimed at my king. Hard rule, every move: before choosing, list every square White's queen can check on and verify each has a defender; defence of the king outranks any central or material gain.
- Game #13 L4 a loss for Claude: Game #13 L4 loss as Black: in the Queen's Gambit after 4.Bg5, do not trade my dark bishop on f6 — play ...Nbd7 and ...c6 and if Bxf6 comes, recapture with the g-pawn, keeping the bishop to hold g7/h8. Also stop 11...dxc4 handing White's queen the active c4-e4-h7 route for free.
- Game #14 L6 a loss for Claude: Game #14 L6 loss as White: 10.Ne5 unblocked the f3 square while Black's bishop on g4 stared at my undefended queen on d1, so 10...Bxd1 won queen for bishop on move 10. Hard rule: while an enemy bishop sits on g4 (or b5/b4 lines), the f3/c3 knight is frozen — before moving any knight, name every enemy piece whose line it is blocking.
- Game #14 L6 a loss for Claude: Game #14 L6 loss as White: after 8...Bxg3 9.hxg3 my king had g3/h-file holes, and 15.f4 plus the g3 pawn left g1-h2 permanently drafty, ending in Qh5 mate on a king walked to h3. Rule: after hxg3 recaptures, do not add f4, keep the king on g1 with a rook on f1-f2, and never march the king up the h-file.
- Game #14 L6 a loss for Claude: Game #14 L6 loss as White: stop the 2.Bf4/3.e3/4.Bd3 London-ish setup that leaves d1 bare and invites ...Bg4/...Bf5 tempo hits. Play 1.d4 d5 2.Nf3 Nf6 3.e3 4.Be2, castle early, and keep a rook on d1 or the queen shielded before any central knight sortie.
- Game #15 L3 a loss for Claude: Game #15 L3 loss as Black: I was a clean pawn up after 14...Rxd4, then 22.Bc5 forked my Rd6 and Be7 and I replied 22...b4 and 23...Ba4 instead of addressing the double attack. Hard rule, every move: list every one of my pieces White attacks; if any is undefended, the only legal choices are defend it, move it, or a capture that wins more.
- Game #15 L3 a loss for Claude: Game #15 L3 loss as Black: 25.Bxe7 and 26.Bxf6 gxf6 stripped my kingside because I let both dark-square defenders go. Once my dark-squared bishop and f6 knight are both loose, treat f6/g7/h7 as critical: keep a rook on f8 or the king on g7, and never allow Bxf6 with a gxf6 recapture while enemy rooks are active.
- Game #15 L3 a loss for Claude: Game #15 L3 loss as Black: in the rook endgame 28...Rd2 abandoned Ba4 to 29.Rxa4, and 34...Ke7 walked into 36.Rd7 mate. Rule: when material is even or down in a rook ending, do not activate a rook while another piece is undefended, and keep the king on f8/g7 behind my own pawns, never on the open file the enemy rook targets.

### Data Analyst

- Game #353 L8 a loss for Claude: Game #353 L8 loss: 10.Nxg5?? hxg5 11.Bxf7+ Kxf7 12.Qh5+ Nxh5 sacrificed two pieces for a pawn with no real attack; before any sac, calculate concrete material recovery or mating line beyond just 'opponent king looks exposed'.
- Game #353 L8 a loss for Claude: Game #353 L8: avoid speculative sacrifices against engines below move 15 unless every forcing line is calculated to a clear material or mating gain; engines defend accurately and punish unsound sacs immediately.
- Game #353 L8 a loss for Claude: Against Stockfish, do not provoke early piece sacrifices on g5/f7 type squares without at least 3-move forced follow-up verified; losing two minors for one pawn is immediately lost.
- Game #354 L5 a loss for Claude: Game #354 L5 loss: 33...h6 weakened the king shelter while queen already infiltrated on e6; avoid pawn moves near your own king (h6, g-file pushes) when opponent's queen/rook can exploit the open lines for a mating attack.
- Game #354 L5 a loss for Claude: Game #354 L5: after allowing queen to reach e6 unchallenged, always check for immediate rook-lift mating threats (Rh1/Rh3 ideas) before making any further king-side pawn moves.
- Game #354 L5 a loss for Claude: Game #354 L5: when down material in a complex middlegame, prioritize king safety and piece defense over counterplay on the kingside; trading queens or consolidating was safer than opening files near own king.
- Game #355 L2 a loss for Claude: Game #355 L2 loss: even against weak levels, do not neglect king safety after early piece trades (Open Lopez line 3...Nf6 4.O-O Nxe4 5.Re1 Nf6 6.Rxe5+); leaving king on f1 with no pawn shelter after 17...Qxh2+ 18.Kf1 Bc4+ is instantly fatal.
- Game #355 L2 a loss for Claude: Game #355 L2: when opponent's queen infiltrates to h2 with check, calculate the follow-up bishop/queen mating net (Bc4+, Qh1#) before committing to Kf1; a king shuffle without blocking or trading is often losing on the spot.
- Game #355 L2 a loss for Claude: Game #355 L2: avoid casual pawn grabs (Bxg5, Nxg5 sequences) that open h-file and diagonal toward your own king; verify king escape squares and piece coverage before initiating simplifying tactics even vs low-skill engines.
- Game #356 L4 a loss for Claude: Game #356 L4 loss: 10...Bd3?? hung a bishop to 11.cxd3 for nothing; never place a piece on a square attacked by an enemy pawn without immediate recapture compensation.
- Game #356 L4 a loss for Claude: Game #356 L4: 13...Bb4?? hung a second piece to 14.axb4; always check all pawn-capture responses (a-,c-,etc.) before moving a bishop to a square near enemy queenside pawns.
- Game #356 L4 a loss for Claude: Game #356 L4: two piece blunders by move 14 made the game lost well before resignation; slow down and verify every bishop/knight move isn't simply hanging to a pawn capture, especially in Caro-Kann Advance structures.

## Current game plan

**Game #357, Claude White vs level 6**

- Opening: 1.e4 as White; meet 1...c5 with 2.Nf3 3.d4 Open Sicilian, or if 1...e5 play Italian 2.Nf3 Nc6 3.Bc4; if Caro-Kann 1...c6 play 2.d4 d5 3.Nc3 Advance/Exchange simply
- Plan: Develop all minor pieces before move 10, castle kingside by move 8, avoid unnecessary trades of your good bishop, and build a small space edge with d4/e4 center before seeking tactics. Convert any material edge by trading pieces but never queens into a weakened king position.
- Principles: Never trade a developed bishop/knight without concrete material or positional gain; Castle by move 8-10 and keep pawn shield intact (no g/h pawn moves unless forced); Check every candidate move for hanging pieces to pawn captures before playing it; Recalculate king safety immediately after any simplification or queen trade; Don't assume Stockfish L6 blunders, verify tactics 3 moves deep
- Watch out for: Any bishop placed where a pawn (a,c,etc.) can capture it next move; Opponent queen or rook lines opening toward your king after trades; Avoid Bd3/Bb4-type moves into enemy pawn capture range as in game 356 loss; Watch for Bh6/Bg5 pins hitting f6-g7 structure near your castled king
- Captain: "We're 0-269, White this time: play solid classical development, keep the bishops safe from pawn captures, and triple-check king safety before every trade."

## Recent meetings

### Huddle · game #370 · Claude (Black) vs SF L3



### Huddle · game #369 · Claude (White) vs SF L6



### Briefing · game #368 · Claude (Black) vs SF L4

- **CAPTAIN**: Meeting cut short: OpenRouter 401: User not found.

## Consulting the engine (analysis API)

Full-strength Stockfish, one position per request, 30 requests per minute per address, thinking time up to 2000 ms.

```sh
curl -s -X POST https://stockfish.finance/api/analyse -H 'content-type: application/json' \
  -d '{"moves":"e4 e5 Nf3 Nc6 Bb5","movetime":800,"multipv":2}'
# or a position:  -d '{"fen":"r1bqkbnr/pppp1ppp/2n5/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3"}'
```

Response: `bestMove` (UCI), `bestMoveSan`, `eval` from White's point of view (`pawns`, or `mate`), `depth`, and `lines` with principal variations in SAN. GET works too: `https://stockfish.finance/api/analyse?moves=e4+e5&movetime=500`.

**MCP**: `tools/stockfish-mcp.mjs` wraps this API as an MCP server with the tools `analyse_position` and `desk_knowledge`. Install with `claude mcp add stockfish -- node /path/to/tools/stockfish-mcp.mjs` or add `{"command":"node","args":["/path/to/tools/stockfish-mcp.mjs"]}` to any MCP client. No dependencies; Node 18+.

## Game index (newest first; PGNs in games.pgn)

| Game | Level | Claude | Winner | How | Plies | Opening |
|---|---|---|---|---|---|---|
| #356 | 4 | B | Stockfish | resignation | 45 | Caro-Kann |
| #355 | 2 | W | Stockfish | resignation | 36 | 1 |
| #354 | 5 | B | Stockfish | checkmate | 69 | 1 |
| #353 | 8 | W | Stockfish | resignation | 30 | 1 |
| #352 | 3 | B | Stockfish | checkmate | 59 | 1 |
| #351 | 6 | W | Stockfish | resignation | 42 | 1 |
| #350 | 4 | B | Stockfish | resignation | 55 | Caro-Kann |
| #349 | 2 | W | Stockfish | resignation | 38 | White, Italian setup |
| #348 | 5 | B | Stockfish | resignation | 59 | Caro-Kann as Black |
| #347 | 8 | W | Stockfish | checkmate | 44 | London System |
| #346 | 3 | B | Stockfish | resignation | 69 | As Black vs 1 |
| #345 | 6 | W | Stockfish | resignation | 48 | 1 |
| #344 | 4 | B | Stockfish | checkmate | 71 | Caro-Kann Defence vs 1 |
| #343 | 2 | W | Stockfish | checkmate | 60 | As White vs Stockfish L2, play 1 |
| #342 | 5 | B | Stockfish | resignation | 61 | Vs 1 |