Shadow Sum: Math Logic Puzzle

The labels have faded. The totals remain. Step into a quiet archive and reconstruct the values of mysterious symbols by comparing rows, columns, regions and diagonals.

Shadow Sum is a math logic puzzle. Each symbol hides one whole number; the same symbol always means the same value on a page, so a single discovery can unlock several clues at once.

How it plays

• Click a symbol, then a number on the pad, or type the number.
• Every row and column must add up to its printed total. A mark beside a total shows when it disagrees.
• Pencil mode keeps candidate notes. Undo is free.
• Worked examples show substitution and how subtracting two clues can cancel symbols. No timer.

200 grids, three daily tiers

A campaign of 200 verified grids across five chapters of the curator's exhibition, three daily pages every day and 90 extra archive pages. A light theme is in Settings.

Controls (PC)

• Mouse: click a symbol, then a number on the pad. The pencil toggles candidate notes.
• Keys: 1-9: enter a value. 0 or Delete: erase. Tab / Shift+Tab: next / previous symbol.
• Keys: Z or Backspace: undo. F1 or H: the rules.
• Enter: Continue on the home screen, or a message's first button (Next). Esc: back / pause; on the home screen it asks before quitting.

The itch.io version

• No ads. No in-app purchases. The full game, once.
• Every help from the mobile version is free and instant, as often as you like: Explain the next deduction, Explain a conflicting value, Open an extra archive page and Use moonlit ink for 3 grids.
• English, Spanish and Brazilian Portuguese: switch any time in Settings. Larger text and reduced motion are there too.
• A 520x960 window that fits a 1080p screen and can be resized. Plays offline, no account.

Credits

Design, code, puzzles and original ambient music and sound design: Crystl Labs. Symbols: Kenney 1-Bit Pack (CC0). Type: Poiret One and Nunito (SIL Open Font License). UI symbols: subsets of Noto Sans Symbols, IBM Plex Mono and Zen Maru Gothic (SIL OFL 1.1). Made with Godot (MIT). Optional crash reports by Sentry (MIT).