diff --git a/animation-worklet/idlharness.any.js b/animation-worklet/idlharness.any.js
new file mode 100644
index 00000000000000..e821a2fee8a3ac
--- /dev/null
+++ b/animation-worklet/idlharness.any.js
@@ -0,0 +1,17 @@
+// META: script=/resources/WebIDLParser.js
+// META: script=/resources/idlharness.js
+
+'use strict';
+
+// https://wicg.github.io/animation-worklet/
+
+idl_test(
+  ['animation-worklet'],
+  ['worklets', 'web-animations', 'html', 'cssom', 'dom'],
+  idl_array => {
+    idl_array.add_objects({
+      WorkletAnimation: ['new WorkletAnimation("name")'],
+      // TODO: WorkletGroupEffect
+    });
+  }
+);
diff --git a/animation-worklet/interfaces.any.js b/animation-worklet/interfaces.any.js
deleted file mode 100644
index 9b1d75649a0989..00000000000000
--- a/animation-worklet/interfaces.any.js
+++ /dev/null
@@ -1,16 +0,0 @@
-// META: script=/resources/WebIDLParser.js
-// META: script=/resources/idlharness.js
-
-'use strict';
-
-// https://wicg.github.io/animation-worklet/
-
-promise_test(async () => {
-  const idl = await (await fetch('/interfaces/animation-worklet.idl')).text();
-  const html = await (await fetch('/interfaces/html.idl')).text();
-  const idlArray = new IdlArray();
-  idlArray.add_idls(idl);
-  idlArray.add_dependency_idls(html);
-  idlArray.test();
-  done();
-}, 'Test driver');
diff --git a/interfaces/animation-worklet.idl b/interfaces/animation-worklet.idl
index e0f5fc2ec200c5..58d0bc51a67be5 100644
--- a/interfaces/animation-worklet.idl
+++ b/interfaces/animation-worklet.idl
@@ -1,35 +1,31 @@
 // GENERATED CONTENT - DO NOT EDIT
-// Content of this file was automatically extracted from the
-// "CSS Animation Worklet API" spec.
-// See: https://wicg.github.io/animation-worklet/
+// Content was automatically extracted by Reffy into reffy-reports
+// (https://github.com/tidoust/reffy-reports)
+// Source: CSS Animation Worklet API (https://wicg.github.io/animation-worklet/)
 
-partial interface Window {
+partial namespace CSS {
     [SameObject] readonly attribute Worklet animationWorklet;
 };
 
-callback VoidFunction = void ();
-
 [ Exposed=AnimationWorklet, Global=AnimationWorklet ]
 interface AnimationWorkletGlobalScope : WorkletGlobalScope {
     void registerAnimator(DOMString name, VoidFunction animatorCtor);
 };
 
 [Constructor (DOMString animatorName,
-              optional (AnimationEffectReadOnly or sequence)? effects = null,
+              optional (AnimationEffect or sequence<AnimationEffect>)? effects = null,
               optional AnimationTimeline? timeline,
               optional any options)]
 interface WorkletAnimation : Animation {
         readonly attribute DOMString animatorName;
 };
 
-interface WorkletGroupEffectReadOnly :  GroupEffectReadOnly {};
-
-interface WorkletGroupEffect :  WorkletGroupEffectReadOnly {};
-WorkletGroupEffect implements AnimationEffectMutable;
-WorkletGroupEffect implements GroupEffectMutable;
+interface WorkletGroupEffect {
+  sequence<AnimationEffect> getChildren();
+};
 
 [Exposed=AnimationWorklet]
-partial interface AnimationEffectReadOnly {
+partial interface AnimationEffect {
     // Intended for use inside Animation Worklet scope to drive the effect.
     attribute double localTime;
 };