diff --git a/package-lock.json b/package-lock.json
index ae2cdf55..24d0780e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4577,6 +4577,7 @@
         "colord": "^2.9.3",
         "dequal": "^2.0.3",
         "hotkeys-js": "^3.13.7",
+        "nanoevents": "^9.0.0",
         "rbush": "^4.0.1",
         "uuid": "^10.0.0"
       },
diff --git a/packages/text-annotator/package.json b/packages/text-annotator/package.json
index fed72f8c..36ffb05a 100644
--- a/packages/text-annotator/package.json
+++ b/packages/text-annotator/package.json
@@ -41,6 +41,7 @@
     "colord": "^2.9.3",
     "dequal": "^2.0.3",
     "hotkeys-js": "^3.13.7",
+    "nanoevents": "^9.0.0",
     "rbush": "^4.0.1",
     "uuid": "^10.0.0"
   }
diff --git a/packages/text-annotator/src/state/TextAnnotationStore.ts b/packages/text-annotator/src/state/TextAnnotationStore.ts
index b03da8ad..25e420f4 100644
--- a/packages/text-annotator/src/state/TextAnnotationStore.ts
+++ b/packages/text-annotator/src/state/TextAnnotationStore.ts
@@ -1,5 +1,9 @@
+import type { Unsubscribe } from 'nanoevents';
 import type { Filter, Origin, Store } from '@annotorious/core';
+
 import type { TextAnnotation } from '../model';
+import type { SpatialTreeEvents } from './spatialTree';
+
 
 export interface TextAnnotationStore<T extends TextAnnotation = TextAnnotation> extends Omit<Store<T>, 'addAnnotation' | 'bulkAddAnnotation'> {
 
@@ -23,6 +27,8 @@ export interface TextAnnotationStore<T extends TextAnnotation = TextAnnotation>
 
   recalculatePositions(): void;
 
+  onRecalculatePositions(callback: SpatialTreeEvents['recalculate']): Unsubscribe;
+
 }
 
 export interface AnnotationRects <T extends TextAnnotation = TextAnnotation> {
diff --git a/packages/text-annotator/src/state/TextAnnotatorState.ts b/packages/text-annotator/src/state/TextAnnotatorState.ts
index 5cb5a4ab..916cbe34 100644
--- a/packages/text-annotator/src/state/TextAnnotatorState.ts
+++ b/packages/text-annotator/src/state/TextAnnotatorState.ts
@@ -11,7 +11,7 @@ import type {
   SelectionState, 
   HoverState, 
 } from '@annotorious/core';
-import { createSpatialTree } from './spatialTree';
+import { createSpatialTree, type SpatialTreeEvents } from './spatialTree';
 import type { TextAnnotation, TextAnnotationTarget } from '../model';
 import type { AnnotationRects, TextAnnotationStore } from './TextAnnotationStore';
 import { isRevived, reviveAnnotation, reviveTarget } from '../utils';
@@ -142,6 +142,7 @@ export const createTextAnnotatorState = <I extends TextAnnotation = TextAnnotati
   const getAnnotationRects = (id: string): DOMRect[] => tree.getAnnotationRects(id);
 
   const recalculatePositions = () => tree.recalculate();
+  const onRecalculatePositions = (callback: SpatialTreeEvents['recalculate']) => tree.on('recalculate', callback);
 
   store.observe(({ changes }) => {
     const deleted = (changes.deleted || []).filter(a => isRevived(a.target.selector));
@@ -170,6 +171,7 @@ export const createTextAnnotatorState = <I extends TextAnnotation = TextAnnotati
       getIntersecting,
       getAt,
       recalculatePositions,
+      onRecalculatePositions,
       updateTarget
     },
     selection,
diff --git a/packages/text-annotator/src/state/spatialTree.ts b/packages/text-annotator/src/state/spatialTree.ts
index 07da5110..4bec2e2a 100644
--- a/packages/text-annotator/src/state/spatialTree.ts
+++ b/packages/text-annotator/src/state/spatialTree.ts
@@ -1,5 +1,7 @@
 import RBush from 'rbush';
 import type { Store } from '@annotorious/core';
+import { createNanoEvents, type Unsubscribe } from 'nanoevents';
+
 import type { TextAnnotation, TextAnnotationTarget } from '../model';
 import {
   isRevived,
@@ -29,12 +31,20 @@ interface IndexedHighlightRect {
 
 }
 
+export interface SpatialTreeEvents {
+
+  recalculate(): void;
+
+}
+
 export const createSpatialTree = <T extends TextAnnotation>(store: Store<T>, container: HTMLElement) => {
 
   const tree = new RBush<IndexedHighlightRect>();
 
   const index = new Map<string, IndexedHighlightRect[]>();
 
+  const emitter = createNanoEvents<SpatialTreeEvents>();
+
   // Helper: converts a single text annotation target to a list of hightlight rects
   const toItems = (target: TextAnnotationTarget, offset: DOMRect): IndexedHighlightRect[] => {
     const rects = target.selector.flatMap(s => {
@@ -180,8 +190,12 @@ export const createSpatialTree = <T extends TextAnnotation>(store: Store<T>, con
 
   const size = () => tree.all().length;
 
-  const recalculate = () =>
+  const recalculate = () => {
     set(store.all().map(a => a.target), true);
+    emitter.emit('recalculate');
+  };
+
+  const on = <E extends keyof SpatialTreeEvents>(event: E, callback: SpatialTreeEvents[E]): Unsubscribe => emitter.on(event, callback);
 
   return {
     all,
@@ -195,7 +209,8 @@ export const createSpatialTree = <T extends TextAnnotation>(store: Store<T>, con
     remove,
     set,
     size,
-    update
+    update,
+    on
   }
 
 }