diff --git a/cruciverb-core/src/config.rs b/cruciverb-core/src/config.rs
new file mode 100644
index 0000000..4672d07
--- /dev/null
+++ b/cruciverb-core/src/config.rs
@@ -0,0 +1,169 @@
+use std::collections::HashMap;
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SymmetryType {
+    Rotational180,
+    Rotational90,
+    Diagonal,
+    Mirror,
+    None,
+}
+
+impl Default for SymmetryType {
+    fn default() -> Self {
+        Self::Rotational180
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum DifficultyPreset {
+    Glyph,
+    Rune,
+    Scroll,
+    Codex,
+    Grimoire,
+}
+
+impl DifficultyPreset {
+    pub fn grid_size(&self) -> usize {
+        match self {
+            Self::Glyph => 5,
+            Self::Rune => 5,
+            Self::Scroll => 9,
+            Self::Codex => 15,
+            Self::Grimoire => 21,
+        }
+    }
+
+    pub fn black_cell_density(&self) -> f64 {
+        match self {
+            Self::Glyph => 0.40,
+            Self::Rune => 0.35,
+            Self::Scroll => 0.28,
+            Self::Codex => 0.20,
+            Self::Grimoire => 0.18,
+        }
+    }
+
+    pub fn frequency_threshold(&self) -> f64 {
+        match self {
+            Self::Glyph => 0.5,
+            Self::Rune => 0.1,
+            Self::Scroll => 0.0,
+            Self::Codex => 0.0,
+            Self::Grimoire => 0.0,
+        }
+    }
+
+    pub fn difficulty_level(&self) -> u8 {
+        match self {
+            Self::Glyph => 0,
+            Self::Rune => 1,
+            Self::Scroll => 2,
+            Self::Codex => 3,
+            Self::Grimoire => 3,
+        }
+    }
+
+    pub fn obscurity_budget(&self) -> f64 {
+        match self {
+            Self::Glyph => 0.0,
+            Self::Rune => 0.0,
+            Self::Scroll => 0.05,
+            Self::Codex => 0.20,
+            Self::Grimoire => 0.20,
+        }
+    }
+
+    pub fn rand_top_base(&self) -> usize {
+        match self {
+            Self::Glyph => 20,
+            Self::Rune => 20,
+            Self::Scroll => 15,
+            Self::Codex => 10,
+            Self::Grimoire => 8,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct GenerationConfig {
+    pub width: usize,
+    pub height: usize,
+    pub symmetry: SymmetryType,
+    pub black_cell_density: f64,
+    pub min_word_length: usize,
+    pub frequency_threshold: f64,
+    pub obscurity_budget: f64,
+    pub max_backtrack: usize,
+    pub max_restarts: usize,
+    pub timeout_seconds: u64,
+    pub seed: Option<u64>,
+    pub cryptic_grid: bool,
+    pub rand_top_base: usize,
+    #[serde(skip)]
+    pub cancelled: Option<Arc<AtomicBool>>,
+    /// Per-word staleness penalties (0.0 = max penalty, 1.0 = no penalty).
+    /// Applied during solver scoring to deprioritize recently used words.
+    #[serde(skip)]
+    pub staleness: Option<Arc<HashMap<String, f64>>>,
+}
+
+impl Default for GenerationConfig {
+    fn default() -> Self {
+        Self {
+            width: 15,
+            height: 15,
+            symmetry: SymmetryType::default(),
+            black_cell_density: 0.22,
+            min_word_length: 3,
+            frequency_threshold: 0.0,
+            obscurity_budget: 0.20,
+            max_backtrack: 5000,
+            max_restarts: 10,
+            timeout_seconds: 90,
+            seed: None,
+            cryptic_grid: false,
+            rand_top_base: 10,
+            cancelled: None,
+            staleness: None,
+        }
+    }
+}
+
+impl GenerationConfig {
+    pub fn rand_top_for_size(size: usize) -> usize {
+        match size {
+            0..=5 => 20,
+            6..=9 => 15,
+            10..=14 => 10,
+            _ => 8,
+        }
+    }
+
+    pub fn from_preset(preset: DifficultyPreset) -> Self {
+        let size = preset.grid_size();
+        let (bt, restarts) = match preset {
+            DifficultyPreset::Codex => (200000, 40),
+            DifficultyPreset::Grimoire => (500000, 60),
+            _ => (5000, 10),
+        };
+        Self {
+            width: size,
+            height: size,
+            black_cell_density: preset.black_cell_density(),
+            frequency_threshold: preset.frequency_threshold(),
+            obscurity_budget: preset.obscurity_budget(),
+            max_backtrack: bt,
+            max_restarts: restarts,
+            rand_top_base: preset.rand_top_base(),
+            ..Default::default()
+        }
+    }
+}