diff --git a/stack-cli/src/main.rs b/stack-cli/src/main.rs
index 318a5805..e481b661 100644
--- a/stack-cli/src/main.rs
+++ b/stack-cli/src/main.rs
@@ -35,7 +35,7 @@ fn main() {
     }
   };
 
-  let mut engine = Engine::new();
+  let mut engine = Engine::new().with_debug_hook(Some(|s| eprintln!("{s}")));
   let mut context = new_context();
 
   #[cfg(feature = "stack-std")]
diff --git a/stack-core/src/engine.rs b/stack-core/src/engine.rs
index becba614..378b5ca6 100644
--- a/stack-core/src/engine.rs
+++ b/stack-core/src/engine.rs
@@ -21,6 +21,7 @@ pub struct Engine {
   modules: HashMap<Symbol, Module>,
   start_time: Option<Instant>,
   timeout: Option<Duration>,
+  debug_hook: Option<fn(String)>,
 }
 
 #[derive(Debug, Clone, PartialEq)]
@@ -37,6 +38,7 @@ impl Engine {
       modules: HashMap::new(),
       start_time: None,
       timeout: None,
+      debug_hook: None,
     }
   }
 
@@ -52,11 +54,22 @@ impl Engine {
     self
   }
 
+  #[inline]
+  pub fn with_debug_hook(mut self, debug_hook: Option<fn(String)>) -> Self {
+    self.debug_hook = debug_hook;
+    self
+  }
+
   #[inline]
   pub fn module(&self, symbol: &Symbol) -> Option<&Module> {
     self.modules.get(symbol)
   }
 
+  #[inline]
+  pub fn debug_hook(&self) -> Option<fn(String)> {
+    self.debug_hook
+  }
+
   pub fn run(
     &self,
     mut context: Context,
diff --git a/stack-core/src/intrinsic.rs b/stack-core/src/intrinsic.rs
index d32b6c77..53529a25 100644
--- a/stack-core/src/intrinsic.rs
+++ b/stack-core/src/intrinsic.rs
@@ -108,6 +108,8 @@ intrinsics! {
   Set => "set",
   Get => "get",
 
+  Debug => "debug",
+  // TODO: These will become STD module items.
   Print => "print",
   Pretty => "pretty",
   Recur => "recur",
@@ -916,6 +918,23 @@ impl Intrinsic {
         }
       }
 
+      // MARK: Debug
+      Self::Debug => {
+        if let Some(debug_hook) = engine.debug_hook() {
+          debug_hook(
+            context
+              .stack()
+              .last()
+              .cloned()
+              .unwrap_or(Expr {
+                kind: ExprKind::Nil,
+                info: None,
+              })
+              .to_string(),
+          );
+        }
+        Ok(context)
+      }
       // MARK: Print
       Self::Print => {
         let val = context.stack_pop(&expr)?;