diff --git a/CLAUDE.md b/CLAUDE.md
index 9fdcbeb..d005958 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -4,13 +4,13 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 ## Project
 
-`viberogue` is a roguelike game written in Rust (edition 2024). It is in early development with no dependencies yet.
+`viberogue` is a ZZT-inspired game-making system written in Rust (edition 2024). The goal is a system where players can create games using a scripting language, similar to the classic DOS game ZZT. It uses **Rhai** for scripting (WASM-compatible, sandboxed, pure Rust).
 
 ## Commands
 
 ```bash
 cargo build          # compile
-cargo run            # build and run
+cargo run            # build and run (loads maps/start.toml)
 cargo test           # run all tests
 cargo test <name>    # run a single test by name (substring match)
 cargo clippy         # lint
@@ -23,8 +23,74 @@ The game is a single Rust binary using **eframe 0.33 / egui 0.33** for the GUI.
 
 `update` is structured in two panels:
 - `egui::TopBottomPanel::top` — menu bar (File → Exit)
-- `egui::CentralPanel::default` — game viewport; use `ui.painter()` to draw directly
+- `egui::CentralPanel::default` — game viewport; rendered with `ui.painter()`
 
-As the codebase grows, game state will live on the `App` struct and game logic will be split into modules under `src/` (map generation, entities, etc.). Keep game logic separate from the egui drawing calls in `update`.
+### Modules
+
+**`src/game.rs`** — all core game types:
+- `Glyph` (`Copy`) — per-cell visual: `ch: char`, `fg/bg: Color32`. `Glyph::player()` is the only constructor used at runtime (colors for board tiles come from the map file).
+- `Element` — behavior: `passable: bool` (future: `opaque`, etc.)
+- `Board` — the complete game unit (ZZT-style "board"): `width`, `height`, `elements: Vec<Element>` (behavior palette), `cells: Vec<(Glyph, usize)>` (row-major; usize indexes into `elements`), `player: Player`, `objects: Vec<ObjectDef>`, `portals: Vec<PortalDef>`. `cells` is `pub(crate)`.
+- `Player` — `x: i32, y: i32`
+- `ObjectDef` / `PortalDef` — parsed from map files, stored on Board; not yet runtime-wired
+- `GameState` — holds `board: Board`; `try_move(dx, dy)` checks passability before moving the player
+
+**`src/map_file.rs`** — map file loading:
+- `MapFile` and friends — serde `Deserialize` types for TOML map files
+- `impl From<MapFile> for Board` — converts a parsed file into a ready-to-use `Board`
+- `pub fn load(path: &str) -> Result<Board, Box<dyn std::error::Error>>` — reads and converts a `.toml` map file
+
+**`src/main.rs`** — app entry point:
+- Loads `maps/start.toml` before creating the window (so board dimensions drive window size)
+- Window min-size = `board.width * CELL_W + 2*PANEL_MARGIN` × `board.height * CELL_H + MENU_H + 2*PANEL_MARGIN`
+- Board is centered in the CentralPanel when the window is larger than minimum
+- `draw_glyph(painter, origin, x, y, glyph)` draws one cell: filled rect (bg) + monospace char (fg)
+- Player is rendered on top of the board using `Glyph::player()`
+- Arrow key input handled via `ctx.input(|i| ...)` before panel rendering
+
+### Map file format (`maps/*.toml`)
+
+XPM-inspired: a `[palette]` maps single characters to `(Glyph, Element)` definitions; `[grid] content` is a TOML multi-line string where each character indexes the palette.
+
+```toml
+[map]
+name = "Room Name"
+width = 60
+height = 25
+player_start = [30, 12]
+
+[palette]
+" " = { passable = true,  ch = " ", fg = "#000000", bg = "#000000" }
+"#" = { passable = false, ch = "#", fg = "#808080", bg = "#606060" }
+
+[grid]
+content = """
+############################################################
+#                                                          #
+############################################################
+"""
+
+[[objects]]          # optional; parsed but not yet runtime-wired
+x = 10
+y = 5
+script = """
+  on_touch(|| { send_message("open"); });
+"""
+
+[[portals]]          # optional; parsed but not yet runtime-wired
+x = 59
+y = 12
+target_map = "cave"
+target_entry = "west_door"
+```
+
+Colors are `"#RRGGBB"` hex strings. `player_start` is a header field — the player is not a board cell. The grid multi-line string's leading newline is trimmed by TOML; trailing newline is handled correctly by `str::lines()`.
+
+### Key design decisions
+
+- **`cells: Vec<(Glyph, usize)>`** — the `usize` element index is intentionally an anonymous tuple field; it only has meaning relative to a specific `Board`'s `elements` palette and cannot be misused as a standalone value.
+- **`Board` is the complete unit** — grid, player, objects, and portals all live on `Board`, matching how ZZT treats a "board". No separate wrapper struct.
+- **Glyph (visual) and Element (behavior) are decoupled** — each cell has its own `Glyph` (so colors can vary per-cell, e.g. fire flickering) but shares `Element` definitions from the palette.
+- **File loading happens in `main()`** before the window is created, so board dimensions are available for window sizing.
 
 eframe runs on its own event loop thread; do not assume single-threaded execution.