diff --git a/crates/js/src/iframe_bridge.rs b/crates/js/src/iframe_bridge.rs
index cf5f003..a3bcf0d 100644
--- a/crates/js/src/iframe_bridge.rs
+++ b/crates/js/src/iframe_bridge.rs
@@ -193,6 +193,17 @@ pub fn init_window_object(vm: &mut Vm, context_id: &str, origin: &str) {
         Value::Function(dispatch_event),
     );
 
+    // window.screen — Screen interface with conservative HD-desktop defaults.
+    let screen_ref = crate::screen::create_screen_object(&mut vm.gc, &mut vm.shapes);
+    set_builtin_prop(
+        &mut vm.gc,
+        &mut vm.shapes,
+        window_ref,
+        "screen",
+        Value::Object(screen_ref),
+    );
+    vm.set_global("screen", Value::Object(screen_ref));
+
     // Set as global.
     vm.set_global("window", Value::Object(window_ref));
 
diff --git a/crates/js/src/lib.rs b/crates/js/src/lib.rs
index 73d5e6f..1cb876f 100644
--- a/crates/js/src/lib.rs
+++ b/crates/js/src/lib.rs
@@ -24,6 +24,7 @@ pub mod media_query;
 pub mod parser;
 pub mod performance;
 pub mod regex;
+pub mod screen;
 pub mod service_worker;
 pub mod service_worker_global;
 pub mod shape;
diff --git a/crates/js/src/screen.rs b/crates/js/src/screen.rs
new file mode 100644
index 0000000..e7d2804
--- /dev/null
+++ b/crates/js/src/screen.rs
@@ -0,0 +1,114 @@
+//! `window.screen` — minimal Screen object for analytics/UA-detection paths.
+//!
+//! Real-world bundles read `screen.width` / `screen.height` to gate desktop vs.
+//! tablet detection (e.g. Bing's `PuxwB9k...js` does
+//! `Math.max(_w.screen.width, _w.screen.height)`). Without this object the
+//! script throws "Cannot read properties of undefined (reading 'width')" and
+//! later hydration steps that depend on the same bundle silently skip.
+//!
+//! `we` is headless and has no notion of a physical display, so the width /
+//! height values are conservative HD-desktop defaults. They are not viewport
+//! aware on purpose — in a real browser `screen` reports the display, not the
+//! window. Pages that want the window size read `innerWidth` / `innerHeight`
+//! instead.
+//!
+//! Spec: <https://drafts.csswg.org/cssom-view/#the-screen-interface>
+
+use crate::builtins::set_builtin_prop;
+use crate::gc::{Gc, GcRef};
+use crate::shape::ShapeTable;
+use crate::vm::*;
+
+const DEFAULT_WIDTH: f64 = 1920.0;
+const DEFAULT_HEIGHT: f64 = 1080.0;
+const DEFAULT_COLOR_DEPTH: f64 = 24.0;
+
+/// Create a `Screen` object populated with conservative HD-desktop defaults.
+pub fn create_screen_object(gc: &mut Gc<HeapObject>, shapes: &mut ShapeTable) -> GcRef {
+    let data = ObjectData::new();
+    let screen_ref = gc.alloc(HeapObject::Object(data));
+
+    for (name, value) in [
+        ("width", DEFAULT_WIDTH),
+        ("height", DEFAULT_HEIGHT),
+        ("availWidth", DEFAULT_WIDTH),
+        ("availHeight", DEFAULT_HEIGHT),
+        ("availLeft", 0.0),
+        ("availTop", 0.0),
+        ("colorDepth", DEFAULT_COLOR_DEPTH),
+        ("pixelDepth", DEFAULT_COLOR_DEPTH),
+    ] {
+        set_builtin_prop(gc, shapes, screen_ref, name, Value::Number(value));
+    }
+
+    screen_ref
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::compiler;
+    use crate::iframe_bridge;
+    use crate::parser::Parser;
+
+    fn eval(vm: &mut Vm, source: &str) -> Value {
+        let program = Parser::parse(source).expect("parse");
+        let func = compiler::compile(&program).expect("compile");
+        vm.execute(&func).expect("execute")
+    }
+
+    #[test]
+    fn screen_width_height_are_available_on_window() {
+        let mut vm = Vm::new();
+        iframe_bridge::init_window_object(&mut vm, "main", "https://example.test");
+
+        let v = eval(&mut vm, "window.screen.width + 'x' + window.screen.height");
+        match v {
+            Value::String(s) => assert_eq!(s, "1920x1080"),
+            other => panic!("expected 1920x1080, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn screen_is_reachable_through_the_window_alias() {
+        let mut vm = Vm::new();
+        iframe_bridge::init_window_object(&mut vm, "main", "https://example.test");
+
+        // The Bing PuxwB9k bundle reaches screen via the `_w` alias for window.
+        let v = eval(&mut vm, "Math.max(_w.screen.width, _w.screen.height)");
+        match v {
+            Value::Number(n) => assert_eq!(n, 1920.0),
+            other => panic!("expected 1920, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn screen_exposes_avail_and_depth_properties() {
+        let mut vm = Vm::new();
+        iframe_bridge::init_window_object(&mut vm, "main", "https://example.test");
+
+        let v = eval(
+            &mut vm,
+            "screen.availWidth + ':' + screen.availHeight + ':' \
+             + screen.availLeft + ':' + screen.availTop + ':' \
+             + screen.colorDepth + ':' + screen.pixelDepth",
+        );
+        match v {
+            Value::String(s) => assert_eq!(s, "1920:1080:0:0:24:24"),
+            other => panic!("expected avail+depth string, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn screen_is_exposed_as_a_bare_global() {
+        let mut vm = Vm::new();
+        iframe_bridge::init_window_object(&mut vm, "main", "https://example.test");
+
+        // Bare `screen` (no `window.` prefix) resolves to the same object.
+        let v = eval(&mut vm, "screen === window.screen");
+        match v {
+            Value::Boolean(b) => assert!(b),
+            other => panic!("expected true, got {other:?}"),
+        }
+    }
+}