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← Build things with code · Mission 7 of 18

Find the move that lost your last chess game

Stockfish, the world's strongest chess engine, is free and runs on your own laptop. You'll talk to it directly, then run a short Python script that marks every inaccuracy, mistake and blunder in a game and shows you the move you should have played.

30 minBeginnerTools: FreeStep 1 free
Tested 9 Oct 2026 · Stockfish 19, python-chess 1.11.2 on Python 3.12 via uv 0.11.9, Intel Core Ultra 7 laptop, Windows 11
Stockfish 19 on your PC, checked against its official fingerprint and its built-in speed test
A feel for how a chess engine thinksyou'll give it a position and watch it search
A Python script that labels every inaccuracy, mistake and blunder in a game, with the better move, and saves an annotated copy of the game
  • A picture of the worst moment of the game, with the move that was played and the move Stockfish wanted
Before you start
  • A Windows, Mac or Linux computer with about 200MB of free disk space (the folder comes to about 100MB, and uv may download Python 3.12 if you don't have it)
  • uv, a small official tool that installs Python projects cleanly. Step 4 shows how to get it
  • A chess game as a PGN file (step 6 shows how to download yours from Chess.com or Lichess), or the sample game
  • No chess engine or Python experience. You'll paste the code, not write it
01/06Download Stockfish and check it's the real thing0 done
STEP 01 of 06~5 min

Download Stockfish and check it's the real thing

Stockfish is one program file. Getting it from the official page, and checking its fingerprint, means you know exactly what you're running.

  1. Chess board seen from Black's side before Black's 9th move, with a red arrow from the knight on f6 to h5 and a green arrow from the pawn on g7 to g5
    Where you're heading: the worst move of a game, found by Stockfish. Red is the move that was played, green is the move that would have held.

  2. Stockfish ↗ is a free, open-source chess engine. It has no board and no buttons: you give it a position, it searches millions of possible moves, and it tells you the best one and who's winning. Many chess apps and websites use it behind the scenes.

  3. Older guides tell you to pick a version called AVX2, BMI2 or VNNI to match your processor. Since Stockfish 19 (September 2026) there's a single Windows download that checks your processor and picks the fastest code by itself, so there's nothing to choose.

  4. On a Mac, Homebrew has Stockfish 19 ready to go. Open Terminal, run the two lines below, then skip to step 2 (use stockfish wherever the steps say .\stockfish\stockfish-windows-x86-64-universal.exe):

    Mac
    mkdir chess-coach && cd chess-coach
brew install stockfish

  5. On Windows, open PowerShell. Make a folder, go into it, and download Stockfish (78MB) with the curl.exe program that comes with Windows:

    Terminal
    mkdir chess-coach
cd chess-coach
curl.exe -L -o stockfish.zip https://github.com/official-stockfish/Stockfish/releases/download/sf_19/stockfish-windows-x86-64-universal.zip

  6. Now print the file's fingerprint (its SHA-256 hash):

    Terminal
    (Get-FileHash stockfish.zip).Hash
    Output
    3C8BF1F9EA66A09350A40DF4F632288285AC206D99F33AB5842C408FC30B48A7

  7. Open the Stockfish 19 release page ↗ and find stockfish-windows-x86-64-universal.zip in the list of files. GitHub shows a sha256: line next to it. It must be the same string of letters and numbers (GitHub shows it in lower case, which doesn't matter). If it matches, unzip the file and delete the zip:

    Terminal
    Expand-Archive stockfish.zip -DestinationPath .
Remove-Item stockfish.zip
dir stockfish\*.exe
    Output
    Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a----        05/09/2026     08:26      103046300 stockfish-windows-x86-64-universal.exe

  8. That 103MB file is the whole engine, including the neural network it uses to judge positions. Nothing gets installed, and nothing is added to your Start menu.

  9. On Linux (x86-64), it's the same idea with the Linux file. Check the fingerprint against the release page, then unpack it:

    Linux
    mkdir chess-coach && cd chess-coach
curl -L -o stockfish.tar.gz https://github.com/official-stockfish/Stockfish/releases/download/sf_19/stockfish-linux-x86-64-universal.tar.gz
sha256sum stockfish.tar.gz
tar -xzf stockfish.tar.gz && rm stockfish.tar.gz
ls stockfish/stockfish-linux-*

  10. On Linux, use ./stockfish/stockfish-linux-x86-64-universal wherever the steps say .\stockfish\stockfish-windows-x86-64-universal.exe.

    TipA newer version out? Use the latest file for your system from the releases page ↗ and change the address in the download command.
✓
CheckpointYour fingerprint matches the one on the release page, and the engine file is inside the stockfish folder (on a Mac, stockfish on its own starts the engine; type quit to leave).
If it breaksA parameter cannot be found that matches parameter name 'L' + 1 more
A parameter cannot be found that matches parameter name 'L'
You typed curl instead of curl.exe. In Windows PowerShell, plain curl is a nickname for a different command that doesn't understand -L. Type curl.exe and it works.
The fingerprint doesn't match
Don't run anything from that zip. Delete it with Remove-Item stockfish.zip, download it again, and check again. Only ever download Stockfish from its GitHub releases page or stockfishchess.org ↗.
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