diff --git a/crates/engine/src/tests/toolsettings.rs b/crates/engine/src/tests/toolsettings.rs
index e896a0ab32..2ec7667bde 100644
--- a/crates/engine/src/tests/toolsettings.rs
+++ b/crates/engine/src/tests/toolsettings.rs
@@ -241,6 +241,69 @@ fn options_are_saved_with_the_preferences() {
     assert_eq!(t.prefs.tool_settings["polygon"]["sides"], json!(9));
 }
 
+#[test]
+fn spiral_decay_is_normalized_for_active_and_inactive_tools_and_preferences() {
+    let mut s = session();
+    for active in [false, true] {
+        select(&mut s, if active { "spiral" } else { "selection" });
+        let options = s.set_tool_option_cmd(&json!({"tool": "spiral", "values": {"decay": 150, "segments": 4, "clockwise": false}})).unwrap();
+        assert_eq!(options["decay"], json!(99.99));
+        assert_eq!(s.tool_options_of("spiral")["decay"], json!(99.99));
+        assert_eq!(s.prefs.tool_settings["spiral"]["decay"], json!(99.99));
+        assert_eq!(s.tool_id(), if active { "spiral" } else { "selection" });
+        select(&mut s, "selection");
+        select(&mut s, "spiral");
+        assert_eq!(s.tool_options()["decay"], json!(99.99));
+    }
+    let saved = serde_json::to_string(&s.prefs).unwrap();
+    let mut restored = session();
+    restored.apply_prefs(serde_json::from_str(&saved).unwrap());
+    select(&mut restored, "spiral");
+    assert_eq!(restored.tool_options(), json!({"decay": 99.99, "segments": 4, "clockwise": false}));
+}
+
+#[test]
+fn legacy_spiral_decay_preferences_report_the_ratio_drawn_after_reopening() {
+    use vectorcraft_geom::Point;
+    use vectorcraft_tools::{PointerEvent, PointerKind};
+
+    // Older versions saved 100–150, although their geometry already capped the ratio at 0.9999.
+    for clockwise in [false, true] {
+        let mut s = session();
+        let mut prefs = Prefs::default();
+        prefs.tool_settings.insert("spiral".into(), json!({"decay": 150, "segments": 4, "clockwise": clockwise}).as_object().unwrap().clone());
+        s.apply_prefs(serde_json::from_str(&serde_json::to_string(&prefs).unwrap()).unwrap());
+        let view = ViewInfo { smart_guides: false, ..Default::default() };
+        s.select_tool("spiral", view).unwrap();
+        let decay = s.tool_options()["decay"].as_f64().unwrap();
+        assert_eq!(decay, 99.99);
+        let before = s.doc().unwrap().history.undo.len();
+        for (kind, x) in [(PointerKind::Down, 200.0), (PointerKind::Drag, 300.0), (PointerKind::Up, 300.0)] {
+            s.pointer(&PointerEvent::new(kind, x, 200.0), view).unwrap();
+        }
+        let d = s.doc().unwrap();
+        assert_eq!(d.history.undo.len(), before + 1);
+        assert_eq!(d.selection.objects.len(), 1);
+        let id = d.selection.objects[0];
+        let path = d.doc.node(id).unwrap().path_data().unwrap().clone();
+        let anchors = &path.subpaths[0].anchors;
+        assert_eq!(anchors.len(), 5);
+        assert!(!path.is_closed());
+        let center = Point::new(200.0, 200.0);
+        // The path runs from the centre end outwards, and decay is per full wind: four quarter-turn
+        // segments give the decay.
+        for pair in anchors.windows(2) {
+            let ratio = pair[0].p.distance(center) / pair[1].p.distance(center);
+            assert!((100.0 * ratio.powi(4) - decay).abs() < 1e-9);
+        }
+        assert_eq!(s.prefs.tool_settings["spiral"]["decay"], json!(99.99));
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert!(s.doc().unwrap().doc.node(id).is_none());
+        s.execute("edit.redo", &json!({})).unwrap();
+        assert_eq!(s.doc().unwrap().doc.node(id).unwrap().path_data().unwrap(), &path);
+    }
+}
+
 /// Escape on a polygon or rounded rectangle drag puts back the side count or corner radius its
 /// arrows changed, in the saved options and the Corner Radius preference too.
 #[test]
diff --git a/crates/tools/src/draw2/family.rs b/crates/tools/src/draw2/family.rs
index 8058101b1c..2e93888d02 100644
--- a/crates/tools/src/draw2/family.rs
+++ b/crates/tools/src/draw2/family.rs
@@ -477,7 +477,8 @@ impl Tool for FamilyTool {
             }
             "slope" => self.slope = v.as_f64().filter(|n| n.is_finite()).map_or(self.slope, |n| n.clamp(-100.0, 100.0)),
             "fillArc" => self.fill_arc = v.as_bool().unwrap_or(self.fill_arc),
-            "decay" => self.decay = v.as_f64().unwrap_or(self.decay).clamp(5.0, 150.0),
+            // Report and persist the decay that shapes::spiral can actually draw.
+            "decay" => self.decay = v.as_f64().unwrap_or(self.decay).clamp(5.0, 99.99),
             "segments" => self.segments = v.as_u64().unwrap_or(10).clamp(2, 1000) as u32,
             "clockwise" => self.clockwise = v.as_bool().unwrap_or(self.clockwise),
             "rows" | "concentric" => self.rows = v.as_u64().unwrap_or(5).min(999) as u32,
@@ -534,6 +535,55 @@ mod tests {
     use crate::testutil::*;
     use vectorcraft_doc::Selection;
 
+    #[test]
+    fn spiral_reports_the_decay_its_command_draws() {
+        let mut t = FamilyTool::new("spiral");
+        assert_eq!(t.options()["decay"], json!(80.0));
+        for (requested, expected) in [(-10.0, 5.0), (5.0, 5.0), (80.0, 80.0), (99.99, 99.99), (100.0, 99.99), (150.0, 99.99), (200.0, 99.99)] {
+            t.set_option("decay", &json!(requested));
+            assert_eq!(t.options()["decay"], json!(expected));
+            let (id, params) = t.command(Point::ZERO, Point::new(100.0, 0.0), Mods::default());
+            assert_eq!(id, "shape.spiral");
+            assert_eq!(params["decay"], json!(expected));
+            // Inspect the actual adjacent radii, not a second copy of the tool's clamp. Decay is per full
+            // wind and a segment is a quarter turn, so four segments give the decay.
+            let path = vectorcraft_geom::shapes::spiral(Point::ZERO, 100.0, params["decay"].as_f64().unwrap(), 2, true);
+            let anchors = &path.subpaths[0].anchors;
+            let outer = anchors[2].p.distance(Point::ZERO);
+            let next = anchors[1].p.distance(Point::ZERO);
+            assert!((100.0 * (next / outer).powi(4) - expected).abs() < 1e-9);
+        }
+        for invalid in [Value::Null, json!("80"), json!(false), json!({})] {
+            t.set_option("decay", &invalid);
+            assert_eq!(t.options()["decay"], json!(99.99));
+        }
+    }
+
+    #[test]
+    fn normalized_spiral_decay_preserves_existing_capped_paths_within_roundoff() {
+        for requested in [100.0, 150.0] {
+            let mut t = FamilyTool::new("spiral");
+            t.set_option("decay", &json!(requested));
+            for clockwise in [false, true] {
+                for segments in [2, 10, 1000] {
+                    for radius in [1.0, 100.0, 1e6] {
+                        let previous = vectorcraft_geom::shapes::spiral(Point::ZERO, radius, requested, segments, clockwise);
+                        let normalized = vectorcraft_geom::shapes::spiral(Point::ZERO, radius, t.decay, segments, clockwise);
+                        let old = &previous.subpaths[0].anchors;
+                        let new = &normalized.subpaths[0].anchors;
+                        assert_eq!(old.len(), new.len());
+                        for (a, b) in old.iter().zip(new) {
+                            assert_eq!(a.kind, b.kind);
+                            for (p, q) in [(a.p, b.p), (a.h_in, b.h_in), (a.h_out, b.h_out)] {
+                                assert!(p.distance(q) <= 1e-10 * (1.0 + radius), "{requested}% / {segments} / {radius}: {p:?} != {q:?}");
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
     #[test]
     fn grid_drag_and_arrows() {
         let (d, _) = doc_with_rect();