diff --git a/crates/pikl-core/src/config.rs b/crates/pikl-core/src/config.rs
new file mode 100644
index 0000000..d646b7e
--- /dev/null
+++ b/crates/pikl-core/src/config.rs
@@ -0,0 +1,29 @@
+//! Runtime configuration for a menu instance. Built from CLI
+//! args or programmatic defaults. This is not the on-disk
+//! config file (that's a future thing).
+
+/// Controls how the menu behaves for a single invocation.
+pub struct MenuConfig {
+    /// JSON key used to extract display labels from object
+    /// items. Ignored for plain-text (string) items.
+    pub label_key: String,
+
+    /// Shell command to run when the user confirms a selection.
+    /// The selected item's JSON is piped to stdin.
+    pub on_select: Option<String>,
+
+    /// Shell command to run when the user cancels.
+    pub on_cancel: Option<String>,
+}
+
+impl Default for MenuConfig {
+    /// Returns a config with `label_key` set to `"label"` and
+    /// no hooks.
+    fn default() -> Self {
+        Self {
+            label_key: "label".to_string(),
+            on_select: None,
+            on_cancel: None,
+        }
+    }
+}
diff --git a/crates/pikl-core/src/error.rs b/crates/pikl-core/src/error.rs
new file mode 100644
index 0000000..c1d3a81
--- /dev/null
+++ b/crates/pikl-core/src/error.rs
@@ -0,0 +1,25 @@
+//! Error types for pikl-core. Every failure mode gets its own
+//! variant. No stringly typed errors, no anyhow.
+
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum PiklError {
+    #[error("io error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("json error: {0}")]
+    Json(#[from] serde_json::Error),
+
+    #[error("hook failed: {command} exited with {status}")]
+    HookFailed {
+        command: String,
+        status: std::process::ExitStatus,
+    },
+
+    #[error("channel closed")]
+    ChannelClosed,
+
+    #[error("{0}")]
+    Script(#[from] crate::script::action_fd::ScriptError),
+}
diff --git a/crates/pikl-core/src/lib.rs b/crates/pikl-core/src/lib.rs
new file mode 100644
index 0000000..0ce92b7
--- /dev/null
+++ b/crates/pikl-core/src/lib.rs
@@ -0,0 +1,22 @@
+//! Core engine for pikl-menu. Handles filtering, navigation,
+//! hooks, and the menu event loop. No rendering or terminal
+//! deps. Frontends are separate crates that talk to this
+//! through channels.
+
+mod model;
+mod query;
+mod runtime;
+pub mod script;
+
+pub mod error;
+
+// Re-export submodules at crate root so the public API stays flat.
+pub use model::event;
+pub use model::item;
+pub use model::traits;
+pub use query::filter;
+pub use query::navigation;
+pub use runtime::hook;
+pub use runtime::input;
+pub use runtime::json_menu;
+pub use runtime::menu;
diff --git a/crates/pikl-core/src/model/event.rs b/crates/pikl-core/src/model/event.rs
new file mode 100644
index 0000000..1769b8b
--- /dev/null
+++ b/crates/pikl-core/src/model/event.rs
@@ -0,0 +1,73 @@
+//! Types that flow between the menu engine and frontends.
+//!
+//! - [`Action`]: commands sent into the menu (keypresses,
+//!   script actions).
+//! - [`MenuEvent`]: notifications sent out to subscribers
+//!   (state changes, terminal events).
+//! - [`ViewState`]: snapshot of what the frontend should
+//!   render right now.
+
+use std::sync::Arc;
+
+use serde_json::Value;
+
+/// A command the menu should process. Frontends and headless
+/// scripts both produce these. The menu loop consumes them
+/// sequentially.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Action {
+    UpdateFilter(String),
+    MoveUp(usize),
+    MoveDown(usize),
+    MoveToTop,
+    MoveToBottom,
+    PageUp(usize),
+    PageDown(usize),
+    Confirm,
+    Cancel,
+    Resize { height: u16 },
+    AddItems(Vec<Value>),
+}
+
+/// Broadcast from the menu loop to all subscribers
+/// (frontends, tests).
+#[derive(Debug, Clone)]
+pub enum MenuEvent {
+    StateChanged(ViewState),
+    Selected(Value),
+    Cancelled,
+}
+
+/// Snapshot of the menu's visible state. Sent on every state
+/// change so frontends can render without querying back into
+/// the engine.
+#[must_use]
+#[derive(Debug, Clone)]
+pub struct ViewState {
+    pub visible_items: Vec<VisibleItem>,
+    /// Index of the cursor within `visible_items`
+    /// (not the full list).
+    pub cursor: usize,
+    pub filter_text: Arc<str>,
+    pub total_items: usize,
+    pub total_filtered: usize,
+}
+
+/// A single item in the current viewport window. Has the
+/// display label pre-resolved and the position in the
+/// filtered list.
+#[must_use]
+#[derive(Debug, Clone)]
+pub struct VisibleItem {
+    pub label: String,
+    pub index: usize,
+}
+
+/// Final outcome of [`crate::menu::MenuRunner::run`]. The
+/// user either picked something or bailed.
+#[must_use]
+#[derive(Debug)]
+pub enum MenuResult {
+    Selected(Value),
+    Cancelled,
+}
diff --git a/crates/pikl-core/src/model/item.rs b/crates/pikl-core/src/model/item.rs
new file mode 100644
index 0000000..4ee6ec3
--- /dev/null
+++ b/crates/pikl-core/src/model/item.rs
@@ -0,0 +1,131 @@
+//! The core data unit. An [`Item`] is a single entry in the
+//! menu, either a plain-text string or a JSON object with
+//! structured fields.
+
+use serde_json::Value;
+
+/// A menu entry wrapping a JSON value. Plain text is stored
+/// as `Value::String`, structured entries as
+/// `Value::Object`. The label is extracted and cached at
+/// construction time so display calls are just a pointer
+/// dereference.
+///
+/// Serializes as the inner Value (transparent for output)
+/// but construction always requires label extraction.
+#[derive(Debug, Clone)]
+pub struct Item {
+    pub value: Value,
+    label_cache: String,
+}
+
+impl Item {
+    /// Create an Item from a JSON value, extracting the display
+    /// label from the given key. String values use the string
+    /// itself. Object values look up the key.
+    pub fn new(value: Value, label_key: &str) -> Self {
+        let label_cache = extract_label(&value, label_key).to_string();
+        Self { value, label_cache }
+    }
+
+    /// Wrap a plain-text string as an Item. Stored internally
+    /// as `Value::String` with the label cached.
+    pub fn from_plain_text(line: &str) -> Self {
+        Self {
+            value: Value::String(line.to_string()),
+            label_cache: line.to_string(),
+        }
+    }
+
+    /// Get the display label for this item. Cached at
+    /// construction time, so this is just a borrow.
+    pub fn label(&self) -> &str {
+        &self.label_cache
+    }
+}
+
+/// Extract the display label from a JSON value.
+fn extract_label<'a>(value: &'a Value, key: &str) -> &'a str {
+    match value {
+        Value::String(s) => s.as_str(),
+        Value::Object(map) => map.get(key).and_then(|v| v.as_str()).unwrap_or(""),
+        _ => "",
+    }
+}
+
+impl serde::Serialize for Item {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        self.value.serialize(serializer)
+    }
+}
+
+impl<'de> serde::Deserialize<'de> for Item {
+    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        let value = Value::deserialize(deserializer)?;
+        // Default to "label" key when deserializing. Callers that need
+        // a different key should construct via Item::new() instead.
+        Ok(Item::new(value, "label"))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+
+    #[test]
+    fn label_from_string() {
+        let item = Item::new(json!("hello"), "label");
+        assert_eq!(item.label(), "hello");
+    }
+
+    #[test]
+    fn label_from_object_with_key() {
+        let item = Item::new(json!({"label": "foo", "value": 42}), "label");
+        assert_eq!(item.label(), "foo");
+    }
+
+    #[test]
+    fn label_from_object_missing_key() {
+        let item = Item::new(json!({"name": "bar"}), "label");
+        assert_eq!(item.label(), "");
+    }
+
+    #[test]
+    fn label_from_object_custom_key() {
+        let item = Item::new(json!({"name": "bar", "label": "ignored"}), "name");
+        assert_eq!(item.label(), "bar");
+    }
+
+    #[test]
+    fn label_from_number() {
+        let item = Item::new(json!(42), "label");
+        assert_eq!(item.label(), "");
+    }
+
+    #[test]
+    fn label_from_null() {
+        let item = Item::new(json!(null), "label");
+        assert_eq!(item.label(), "");
+    }
+
+    #[test]
+    fn from_plain_text() {
+        let item = Item::from_plain_text("hello world");
+        assert_eq!(item.label(), "hello world");
+        assert!(item.value.is_string());
+    }
+
+    #[test]
+    fn serialize_string_item() {
+        let item = Item::from_plain_text("test");
+        let json = serde_json::to_string(&item).unwrap_or_default();
+        assert_eq!(json, "\"test\"");
+    }
+
+    #[test]
+    fn serialize_object_item() {
+        let item = Item::new(json!({"label": "foo"}), "label");
+        let json = serde_json::to_string(&item).unwrap_or_default();
+        assert_eq!(json, r#"{"label":"foo"}"#);
+    }
+}
diff --git a/crates/pikl-core/src/model/mod.rs b/crates/pikl-core/src/model/mod.rs
new file mode 100644
index 0000000..150b115
--- /dev/null
+++ b/crates/pikl-core/src/model/mod.rs
@@ -0,0 +1,3 @@
+pub mod event;
+pub mod item;
+pub mod traits;
diff --git a/crates/pikl-core/src/model/traits.rs b/crates/pikl-core/src/model/traits.rs
new file mode 100644
index 0000000..537aebb
--- /dev/null
+++ b/crates/pikl-core/src/model/traits.rs
@@ -0,0 +1,41 @@
+//! Trait abstractions for the menu data layer. [`Menu`]
+//! is what the event loop drives. [`MenuItem`] is the display
+//! contract for a single entry. Different backends (JSON,
+//! CSV, Postgres, etc.) implement these.
+
+/// Display contract for a single entry in a menu.
+/// Provides a label for display and serialization for output.
+pub trait MenuItem: Send + Sync + 'static {
+    /// Human-readable display text for this entry.
+    fn label(&self) -> &str;
+
+    /// Serialize this entry for structured output (stdout, hooks).
+    fn serialize(&self) -> serde_json::Value;
+}
+
+/// A filterable collection that the menu event loop drives.
+/// Each implementation owns its data and handles filtering
+/// internally. The event loop only needs labels (strings)
+/// and serialized output (JSON values).
+pub trait Menu: Send + 'static {
+    /// Total number of items before filtering.
+    fn total(&self) -> usize;
+
+    /// Apply a filter query. Implementations decide how to
+    /// match (fuzzy, regex, exact, SQL WHERE, etc.).
+    fn apply_filter(&mut self, query: &str);
+
+    /// Number of items that passed the current filter.
+    fn filtered_count(&self) -> usize;
+
+    /// Get the display label for a filtered item by its
+    /// position in the filtered results.
+    fn filtered_label(&self, filtered_index: usize) -> Option<&str>;
+
+    /// Add raw values from streaming input or AddItems actions.
+    fn add_raw(&mut self, values: Vec<serde_json::Value>);
+
+    /// Get the JSON value of a filtered item for output.
+    /// Returns a reference to the stored value.
+    fn serialize_filtered(&self, filtered_index: usize) -> Option<&serde_json::Value>;
+}