diff --git a/Userland/Libraries/LibWeb/Animations/Animation.cpp b/Userland/Libraries/LibWeb/Animations/Animation.cpp
index 532650005c..9967744060 100644
--- a/Userland/Libraries/LibWeb/Animations/Animation.cpp
+++ b/Userland/Libraries/LibWeb/Animations/Animation.cpp
@@ -10,6 +10,7 @@
 #include <LibWeb/Animations/AnimationPlaybackEvent.h>
 #include <LibWeb/Animations/DocumentTimeline.h>
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/CSS/CSSAnimation.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/HTML/Scripting/TemporaryExecutionContext.h>
 #include <LibWeb/HTML/Window.h>
@@ -297,6 +298,44 @@ Bindings::AnimationPlayState Animation::play_state() const
     return Bindings::AnimationPlayState::Running;
 }
 
+// https://www.w3.org/TR/web-animations-1/#replaceable-animation
+bool Animation::is_replaceable() const
+{
+    // An animation is replaceable if all of the following conditions are true:
+
+    // - The existence of the animation is not prescribed by markup. That is, it is not a CSS animation with an owning
+    //   element, nor a CSS transition with an owning element.
+    // FIXME: Check for transitions
+    if (is_css_animation() && static_cast<CSS::CSSAnimation const*>(this)->owning_element())
+        return false;
+
+    // - The animation's play state is finished.
+    if (play_state() != Bindings::AnimationPlayState::Finished)
+        return false;
+
+    // - The animation's replace state is not removed.
+    if (replace_state() == Bindings::AnimationReplaceState::Removed)
+        return false;
+
+    // - The animation is associated with a monotonically increasing timeline.
+    if (!m_timeline || !m_timeline->is_monotonically_increasing())
+        return false;
+
+    // - The animation has an associated effect.
+    if (!m_effect)
+        return false;
+
+    // - The animation's associated effect is in effect.
+    if (!m_effect->is_in_effect())
+        return false;
+
+    // - The animation's associated effect has an effect target.
+    if (!m_effect->target())
+        return false;
+
+    return true;
+}
+
 // https://www.w3.org/TR/web-animations-1/#dom-animation-play
 WebIDL::ExceptionOr<void> Animation::play()
 {
diff --git a/Userland/Libraries/LibWeb/Animations/Animation.h b/Userland/Libraries/LibWeb/Animations/Animation.h
index 8acce8e321..3b5b675045 100644
--- a/Userland/Libraries/LibWeb/Animations/Animation.h
+++ b/Userland/Libraries/LibWeb/Animations/Animation.h
@@ -50,6 +50,7 @@ public:
 
     Bindings::AnimationPlayState play_state() const;
 
+    bool is_replaceable() const;
     Bindings::AnimationReplaceState replace_state() const { return m_replace_state; }
 
     // https://www.w3.org/TR/web-animations-1/#dom-animation-pending
diff --git a/Userland/Libraries/LibWeb/Animations/AnimationEffect.cpp b/Userland/Libraries/LibWeb/Animations/AnimationEffect.cpp
index 74f4bdf3f7..e8192630c5 100644
--- a/Userland/Libraries/LibWeb/Animations/AnimationEffect.cpp
+++ b/Userland/Libraries/LibWeb/Animations/AnimationEffect.cpp
@@ -264,6 +264,14 @@ Optional<double> AnimationEffect::active_time_using_fill(Bindings::FillMode fill
     return {};
 }
 
+// https://www.w3.org/TR/web-animations-1/#in-effect
+bool AnimationEffect::is_in_effect() const
+{
+    // An animation effect is in effect if its active time, as calculated according to the procedure in
+    // §4.8.3.1 Calculating the active time, is not unresolved.
+    return active_time().has_value();
+}
+
 // https://www.w3.org/TR/web-animations-1/#before-active-boundary-time
 double AnimationEffect::before_active_boundary_time() const
 {
diff --git a/Userland/Libraries/LibWeb/Animations/AnimationEffect.h b/Userland/Libraries/LibWeb/Animations/AnimationEffect.h
index a7abf938a2..d74af2557b 100644
--- a/Userland/Libraries/LibWeb/Animations/AnimationEffect.h
+++ b/Userland/Libraries/LibWeb/Animations/AnimationEffect.h
@@ -104,6 +104,7 @@ public:
     double active_duration() const;
     Optional<double> active_time() const;
     Optional<double> active_time_using_fill(Bindings::FillMode) const;
+    bool is_in_effect() const;
 
     double before_active_boundary_time() const;
     double after_active_boundary_time() const;