diff --git a/crates/oxide_builtins/src/object.rs b/crates/oxide_builtins/src/object.rs
index 005f07ce..1dbd8914 100644
--- a/crates/oxide_builtins/src/object.rs
+++ b/crates/oxide_builtins/src/object.rs
@@ -339,62 +339,132 @@ macro_rules! native_try {
 
 pub fn object_freeze<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     if args.len() < 2 {
-        return NativeResult::Ok(JsValue::undefined());
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.freeze called on non-object"));
     }
     let val = vm.reg(args[1]);
     if !val.is_object() || val.as_js_object_ptr().is_null() {
         return NativeResult::Ok(val);
     }
+    let obj_ptr = val.as_js_object_ptr();
+    unsafe {
+        (*obj_ptr).set_frozen(true);
+        (*obj_ptr).set_extensible(false);
+    }
     NativeResult::Ok(val)
 }
 
 pub fn object_seal<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     if args.len() < 2 {
-        return NativeResult::Ok(JsValue::undefined());
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.seal called on non-object"));
     }
     let val = vm.reg(args[1]);
     if !val.is_object() || val.as_js_object_ptr().is_null() {
         return NativeResult::Ok(val);
     }
+    let obj_ptr = val.as_js_object_ptr();
+    unsafe {
+        (*obj_ptr).set_sealed(true);
+        (*obj_ptr).set_extensible(false);
+    }
     NativeResult::Ok(val)
 }
 
 pub fn object_prevent_extensions<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     if args.len() < 2 {
-        return NativeResult::Ok(JsValue::undefined());
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.preventExtensions called on non-object"));
     }
     let val = vm.reg(args[1]);
     if !val.is_object() || val.as_js_object_ptr().is_null() {
         return NativeResult::Ok(val);
     }
+    let obj_ptr = val.as_js_object_ptr();
+    unsafe {
+        (*obj_ptr).set_extensible(false);
+    }
     NativeResult::Ok(val)
 }
 
 pub fn object_is_frozen<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     if args.len() < 2 {
-        return NativeResult::Ok(JsValue::bool(true));
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.isFrozen called on non-object"));
     }
     let val = vm.reg(args[1]);
-    if !val.is_object() || val.as_js_object_ptr().is_null() {
+    if !val.is_object() {
         return NativeResult::Ok(JsValue::bool(true));
     }
-    NativeResult::Ok(JsValue::bool(false))
+    let obj_ptr = val.as_js_object_ptr();
+    if obj_ptr.is_null() {
+        return NativeResult::Ok(JsValue::bool(true));
+    }
+    let obj = unsafe { &*obj_ptr };
+    if obj.is_frozen() {
+        return NativeResult::Ok(JsValue::bool(true));
+    }
+    if obj.is_extensible() {
+        return NativeResult::Ok(JsValue::bool(false));
+    }
+    let keys = walk_own_keys(vm, obj);
+    for (_si, offset) in keys {
+        if let Some(meta) = obj.prop_meta_at(offset) {
+            if meta.attributes.configurable() {
+                return NativeResult::Ok(JsValue::bool(false));
+            }
+            if !meta.is_accessor && meta.attributes.writable() {
+                return NativeResult::Ok(JsValue::bool(false));
+            }
+        } else {
+            return NativeResult::Ok(JsValue::bool(false));
+        }
+    }
+    NativeResult::Ok(JsValue::bool(true))
 }
 
 pub fn object_is_sealed<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     if args.len() < 2 {
-        return NativeResult::Ok(JsValue::bool(true));
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.isSealed called on non-object"));
     }
     let val = vm.reg(args[1]);
-    if !val.is_object() || val.as_js_object_ptr().is_null() {
+    if !val.is_object() {
         return NativeResult::Ok(JsValue::bool(true));
     }
-    NativeResult::Ok(JsValue::bool(false))
+    let obj_ptr = val.as_js_object_ptr();
+    if obj_ptr.is_null() {
+        return NativeResult::Ok(JsValue::bool(true));
+    }
+    let obj = unsafe { &*obj_ptr };
+    if obj.is_sealed() {
+        return NativeResult::Ok(JsValue::bool(true));
+    }
+    if obj.is_extensible() {
+        return NativeResult::Ok(JsValue::bool(false));
+    }
+    let keys = walk_own_keys(vm, obj);
+    for (_si, offset) in keys {
+        if let Some(meta) = obj.prop_meta_at(offset) {
+            if meta.attributes.configurable() {
+                return NativeResult::Ok(JsValue::bool(false));
+            }
+        } else {
+            return NativeResult::Ok(JsValue::bool(false));
+        }
+    }
+    NativeResult::Ok(JsValue::bool(true))
 }
 
 pub fn object_is_extensible<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
-    native_try!(require_obj_arg(vm, args, "isExtensible"));
-    NativeResult::Ok(JsValue::bool(true))
+    if args.len() < 2 {
+        return NativeResult::Err(crate::error::create_type_error(vm, "Object.isExtensible called on non-object"));
+    }
+    let val = vm.reg(args[1]);
+    if !val.is_object() {
+        return NativeResult::Ok(JsValue::bool(false));
+    }
+    let obj_ptr = val.as_js_object_ptr();
+    if obj_ptr.is_null() {
+        return NativeResult::Ok(JsValue::bool(false));
+    }
+    let obj = unsafe { &*obj_ptr };
+    NativeResult::Ok(JsValue::bool(obj.is_extensible()))
 }
 
 pub fn object_get_own_property_names<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
diff --git a/crates/oxide_builtins/tests/object_boundary_tests.rs b/crates/oxide_builtins/tests/object_boundary_tests.rs
index 4bd14dfc..06dc7182 100644
--- a/crates/oxide_builtins/tests/object_boundary_tests.rs
+++ b/crates/oxide_builtins/tests/object_boundary_tests.rs
@@ -99,3 +99,47 @@ fn test_assign_merges_two_sources() {
     let (_vm, result) = eval("var t = {a:1}; Object.assign(t, {b:2}); t.b").unwrap();
     assert!(result.is_int() || result.is_double(), "Object.assign should copy from source");
 }
+
+#[test]
+fn test_integrity_freeze_returns_object() {
+    let (_vm, result) = eval("var o = {x:1}; Object.freeze(o) === o").unwrap();
+    assert!(result.is_bool() && result.as_bool(), "freeze should return the object");
+}
+
+#[test]
+fn test_integrity_freeze_sets_non_extensible() {
+    let (_vm, result) = eval("var o = {x:1}; Object.freeze(o); Object.isExtensible(o)").unwrap();
+    assert!(result.is_bool() && !result.as_bool(), "freeze should set non-extensible");
+}
+
+#[test]
+fn test_integrity_seal_non_extensible() {
+    let (_vm, result) = eval("var o = {x:1}; Object.seal(o); Object.isExtensible(o)").unwrap();
+    assert!(result.is_bool() && !result.as_bool(), "seal should set non-extensible");
+}
+
+#[test]
+fn test_integrity_prevent_extensions() {
+    let (_vm, result) = eval("var o = {x:1}; Object.preventExtensions(o); Object.isExtensible(o)").unwrap();
+    assert!(result.is_bool() && !result.as_bool(), "preventExtensions should set non-extensible");
+}
+
+#[test]
+fn test_is_frozen_non_object_returns_true() {
+    let (_vm, result) = eval("Object.isFrozen(42)").unwrap();
+    assert!(result.is_bool() && result.as_bool(), "non-object should be frozen per ES spec");
+}
+
+#[test]
+fn test_is_sealed_non_object_returns_true() {
+    let (_vm, result) = eval("Object.isSealed(42)").unwrap();
+    assert!(result.is_bool() && result.as_bool(), "non-object should be sealed per ES spec");
+}
+
+#[test]
+fn test_is_extensible_non_object_returns_false() {
+    let (_vm, result) = eval("Object.isExtensible(42)").unwrap();
+    assert!(result.is_bool() && !result.as_bool(), "non-object should not be extensible per ES spec");
+}
+
+
diff --git a/crates/oxide_builtins/tests/object_integrity_tests.rs b/crates/oxide_builtins/tests/object_integrity_tests.rs
new file mode 100644
index 00000000..ce1b08b2
--- /dev/null
+++ b/crates/oxide_builtins/tests/object_integrity_tests.rs
@@ -0,0 +1,59 @@
+use oxide_types::object::JsObject;
+use oxide_types::value::JsValue;
+
+fn new_obj() -> JsObject {
+    JsObject::new_empty(0, JsValue::null())
+}
+
+#[test]
+fn test_set_frozen() {
+    let mut obj = new_obj();
+    assert!(!obj.is_frozen());
+    obj.set_frozen(true);
+    assert!(obj.is_frozen());
+}
+
+#[test]
+fn test_set_sealed() {
+    let mut obj = new_obj();
+    assert!(!obj.is_sealed());
+    obj.set_sealed(true);
+    assert!(obj.is_sealed());
+}
+
+#[test]
+fn test_frozen_and_sealed_independent() {
+    let mut obj = new_obj();
+    obj.set_frozen(true);
+    assert!(obj.is_frozen());
+    assert!(!obj.is_sealed());
+    obj.set_sealed(true);
+    assert!(obj.is_frozen());
+    assert!(obj.is_sealed());
+    obj.set_frozen(false);
+    assert!(!obj.is_frozen());
+    assert!(obj.is_sealed());
+}
+
+#[test]
+fn test_defaults_are_false() {
+    let obj = new_obj();
+    assert!(!obj.is_frozen());
+    assert!(!obj.is_sealed());
+}
+
+#[test]
+fn test_clear_frozen() {
+    let mut obj = new_obj();
+    obj.set_frozen(true);
+    obj.set_frozen(false);
+    assert!(!obj.is_frozen());
+}
+
+#[test]
+fn test_clear_sealed() {
+    let mut obj = new_obj();
+    obj.set_sealed(true);
+    obj.set_sealed(false);
+    assert!(!obj.is_sealed());
+}
diff --git a/crates/oxide_types/src/object.rs b/crates/oxide_types/src/object.rs
index 72208698..e842ce8d 100644
--- a/crates/oxide_types/src/object.rs
+++ b/crates/oxide_types/src/object.rs
@@ -574,6 +574,30 @@ impl JsObject {
         }
     }
 
+    pub fn is_frozen(&self) -> bool {
+        (self._pad) & 1 != 0
+    }
+
+    pub fn set_frozen(&mut self, frozen: bool) {
+        if frozen {
+            self._pad |= 1 << 0;
+        } else {
+            self._pad &= !(1 << 0);
+        }
+    }
+
+    pub fn is_sealed(&self) -> bool {
+        (self._pad >> 1) & 1 != 0
+    }
+
+    pub fn set_sealed(&mut self, sealed: bool) {
+        if sealed {
+            self._pad |= 1 << 1;
+        } else {
+            self._pad &= !(1 << 1);
+        }
+    }
+
     pub fn is_set(&self) -> bool {
         (self.header >> 24) & 1 != 0
     }