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NumChess

Chess for the NumWorks N0120 calculator.
12 bots, endless puzzles and a two-player clock, in a native app of about 20 KB.

Download chess.nwa  ·  Install  ·  Controls  ·  Build

Highlights

• 12 bots, from Pip (150) to Atlas (2100), most of them at the beginner end.
• Endless puzzles created on the calculator: mate in 1, 2 or 3, or find the one winning move. A rating and a streak track your progress.
• Two-player mode with a chess clock. The board turns to face whoever is to move.
• Fast and small: about 20 KB installed. The piece set takes 658 bytes, and there's no puzzle database.

Main menu

A game against Nova

Play the bots

Pick an opponent and a color (White, random or Black), then play. Each bot beats the one below it in bot-vs-bot matches. The Elo numbers are rough estimates.

Choose a bot and your color	Atlas, the strongest bot, thinks up to 2.5 s per move
Legal moves as dots, captures as rings	Check glow, last-move highlight, captured pieces with material count
Promotion picker	Result card with rematch
Back opens the pause menu: undo, flip, resign

Puzzles

Every puzzle is generated on the calculator. It plays a quick game between a careful side and a blunder-prone side, then stops at a position with a forced mate or a single winning move. Puzzles never run out, and the app stores none of them.

• Modes: Mix, Mate in 1, Mate in 2, Mate in 3 and Best move.
• Opening move: each puzzle starts by playing the opponent's last move, which is the mistake you punish.
• Accepted solutions: any move that still forces the mate counts. The opponent defends as stubbornly as possible.
• Rating: it goes up or down after each puzzle, and Mix and Best move pick puzzles near it. A streak counts your solves in a row.
• Pause menu: Hint highlights the piece to move, Solution plays the answer, and Next skips.
• Speed: the next puzzle is prepared while you look at the solved one.

Puzzle modes	Mate in 1: the pill shows who is to move
Mate in 3 as Black: the board flips for you	Best move: find the knight fork
Hint	Wrong move: it's taken back and your rating drops
Solved	Hint, solution, next

Two players

Play over the board with a chess clock. After every move the board turns to face the next player. If you prefer a fixed board, use Flip in the pause menu.

1+0 to 30+0, or no clock

The active clock is lit

Under 10 s it turns red and shows tenths

All the rules are included: castling, en passant, underpromotion, and draws by stalemate, threefold repetition, the 50-move rule or insufficient material. You can also agree to a draw or resign.

Controls

Key	Action
Arrows	Move the cursor (it wraps around the edges)
OK or EXE	Select a piece, then play a move
Back	Deselect, open the pause menu, or go back a screen
⌫	Undo
Home	Quit

Install

1. Download chess.nwa from the latest release.
2. Plug the calculator into your computer and open my.numworks.com/apps in Chrome or Edge.
3. Upload chess.nwa. Chess appears at the end of the calculator's home screen.

If you're building from source, make run builds and installs in one step.

Small by design

Installed size	about 20 KB (20,074 bytes of code and data)
Piece set	658 bytes: 3-bit anti-aliased sprites, and symmetric pieces store only half
Puzzle data	none: every puzzle is generated live
RAM	about 52 KB, all static, no heap

• Engine (src/chess.c):
  • 0x88 board with incremental hashing and evaluation.
  • PeSTO piece-square tables, mirrored and packed into 384 bytes.
  • Alpha-beta search with PVS, a transposition table, null-move pruning, late-move reductions, killer moves and history heuristics.
  • A mate solver.
  • Bots get weaker through search depth, evaluation noise and occasional random moves.
• Graphics (src/main.c):
  • Each board square is drawn in one pass: highlights, check glow, move hints and the piece, all blended in RGB565.
  • Rounded cards and circles are anti-aliased.
  • Moves animate with an ease-out curve.
  • Text uses the calculator's own fonts.
• Pieces are drawn as signed-distance shapes by tools/pieces.py and rendered to sprites. tools/icon.py makes the app icon the same way.
• Build: -Os, LTO, and small replacements for the libc routines.

Build

Requirements: the ARM embedded toolchain (arm-none-eabi-gcc) and Node.js, which make uses to fetch NumWorks' nwlink SDK.

make          # output/chess.nwa
make check    # link it the way the calculator does and print the installed size
make test     # engine tests on the host: perft on six positions, hashing, search benchmark
make run      # install on a connected calculator

Every push is built by GitHub Actions. Pushing a v* tag publishes a release with chess.nwa attached.

License

NumChess is licensed under the GNU General Public License v3.0. Copyright (c) 2026 Mason Chen.