diff --git a/src/index.js b/src/index.js
index d23c37f5..781e8eb4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -92,7 +92,9 @@ export {
   convertUpdateFormatV2ToV1,
   obfuscateUpdate,
   obfuscateUpdateV2,
-  UpdateEncoderV1
+  UpdateEncoderV1,
+  equalDeleteSets,
+  snapshotContainsUpdate
 } from './internals.js'
 
 const glo = /** @type {any} */ (typeof globalThis !== 'undefined'
diff --git a/src/utils/DeleteSet.js b/src/utils/DeleteSet.js
index 429c3b91..e5e964dd 100644
--- a/src/utils/DeleteSet.js
+++ b/src/utils/DeleteSet.js
@@ -328,3 +328,23 @@ export const readAndApplyDeleteSet = (decoder, transaction, store) => {
   }
   return null
 }
+
+/**
+ * @param {DeleteSet} ds1
+ * @param {DeleteSet} ds2
+ */
+export const equalDeleteSets = (ds1, ds2) => {
+  if (ds1.clients.size !== ds2.clients.size) return false
+  ds1.clients.forEach((deleteItems1, client) => {
+    const deleteItems2 = /** @type {Array<import('../internals.js').DeleteItem>} */ (ds2.clients.get(client))
+    if (deleteItems2 === undefined || deleteItems1.length !== deleteItems2.length) return false
+    for (let i = 0; i < deleteItems1.length; i++) {
+      const di1 = deleteItems1[i]
+      const di2 = deleteItems2[i]
+      if (di1.clock !== di2.clock || di1.len !== di2.len) {
+        return false
+      }
+    }
+  })
+  return true
+}
diff --git a/src/utils/Snapshot.js b/src/utils/Snapshot.js
index a13bb559..dfd82c86 100644
--- a/src/utils/Snapshot.js
+++ b/src/utils/Snapshot.js
@@ -15,7 +15,10 @@ import {
   findIndexSS,
   UpdateEncoderV2,
   applyUpdateV2,
-  DSEncoderV1, DSEncoderV2, DSDecoderV1, DSDecoderV2, Transaction, Doc, DeleteSet, Item // eslint-disable-line
+  LazyStructReader,
+  equalDeleteSets,
+  UpdateDecoderV1, UpdateDecoderV2, DSEncoderV1, DSEncoderV2, DSDecoderV1, DSDecoderV2, Transaction, Doc, DeleteSet, Item, // eslint-disable-line
+  mergeDeleteSets
 } from '../internals.js'
 
 import * as map from 'lib0/map'
@@ -147,7 +150,7 @@ export const splitSnapshotAffectedStructs = (transaction, snapshot) => {
         getItemCleanStart(transaction, createID(client, clock))
       }
     })
-    iterateDeletedStructs(transaction, snapshot.ds, item => {})
+    iterateDeletedStructs(transaction, snapshot.ds, _item => {})
     meta.add(snapshot)
   }
 }
@@ -207,3 +210,28 @@ export const createDocFromSnapshot = (originDoc, snapshot, newDoc = new Doc()) =
   applyUpdateV2(newDoc, encoder.toUint8Array(), 'snapshot')
   return newDoc
 }
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} [YDecoder]
+ */
+export const snapshotContainsUpdateV2 = (snapshot, update, YDecoder = UpdateDecoderV2) => {
+  const structs = []
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    structs.push(curr)
+    if ((snapshot.sv.get(curr.id.client) || 0) < curr.id.clock + curr.length) {
+      return false
+    }
+  }
+  const mergedDS = mergeDeleteSets([snapshot.ds, readDeleteSet(updateDecoder)])
+  return equalDeleteSets(snapshot.ds, mergedDS)
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {Uint8Array} update
+ */
+export const snapshotContainsUpdate = (snapshot, update) => snapshotContainsUpdateV2(snapshot, update, UpdateDecoderV1)
diff --git a/src/utils/encoding.js b/src/utils/encoding.js
index 56e5dac1..83e1b91f 100644
--- a/src/utils/encoding.js
+++ b/src/utils/encoding.js
@@ -88,7 +88,7 @@ export const writeClientsStructs = (encoder, store, _sm) => {
       sm.set(client, clock)
     }
   })
-  getStateVector(store).forEach((clock, client) => {
+  getStateVector(store).forEach((_clock, client) => {
     if (!_sm.has(client)) {
       sm.set(client, 0)
     }
@@ -98,8 +98,7 @@ export const writeClientsStructs = (encoder, store, _sm) => {
   // Write items with higher client ids first
   // This heavily improves the conflict algorithm.
   array.from(sm.entries()).sort((a, b) => b[0] - a[0]).forEach(([client, clock]) => {
-    // @ts-ignore
-    writeStructs(encoder, store.clients.get(client), client, clock)
+    writeStructs(encoder, /** @type {Array<GC|Item>} */ (store.clients.get(client)), client, clock)
   })
 }
 
diff --git a/tests/snapshot.tests.js b/tests/snapshot.tests.js
index cd3e4773..d72e7ba7 100644
--- a/tests/snapshot.tests.js
+++ b/tests/snapshot.tests.js
@@ -3,9 +3,9 @@ import * as t from 'lib0/testing'
 import { init } from './testHelper.js'
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testBasic = tc => {
+export const testBasic = _tc => {
   const ydoc = new Y.Doc({ gc: false })
   ydoc.getText().insert(0, 'world!')
   const snapshot = Y.snapshot(ydoc)
@@ -15,9 +15,9 @@ export const testBasic = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testBasicRestoreSnapshot = tc => {
+export const testBasicRestoreSnapshot = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, ['hello'])
   const snap = Y.snapshot(doc)
@@ -30,9 +30,9 @@ export const testBasicRestoreSnapshot = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testEmptyRestoreSnapshot = tc => {
+export const testEmptyRestoreSnapshot = _tc => {
   const doc = new Y.Doc({ gc: false })
   const snap = Y.snapshot(doc)
   snap.sv.set(9999, 0)
@@ -50,9 +50,9 @@ export const testEmptyRestoreSnapshot = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testRestoreSnapshotWithSubType = tc => {
+export const testRestoreSnapshotWithSubType = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, [new Y.Map()])
   const subMap = doc.getArray('array').get(0)
@@ -73,9 +73,9 @@ export const testRestoreSnapshotWithSubType = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testRestoreDeletedItem1 = tc => {
+export const testRestoreDeletedItem1 = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, ['item1', 'item2'])
 
@@ -89,9 +89,9 @@ export const testRestoreDeletedItem1 = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testRestoreLeftItem = tc => {
+export const testRestoreLeftItem = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, ['item1'])
   doc.getMap('map').set('test', 1)
@@ -107,9 +107,9 @@ export const testRestoreLeftItem = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testDeletedItemsBase = tc => {
+export const testDeletedItemsBase = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, ['item1'])
   doc.getArray('array').delete(0)
@@ -123,9 +123,9 @@ export const testDeletedItemsBase = tc => {
 }
 
 /**
- * @param {t.TestCase} tc
+ * @param {t.TestCase} _tc
  */
-export const testDeletedItems2 = tc => {
+export const testDeletedItems2 = _tc => {
   const doc = new Y.Doc({ gc: false })
   doc.getArray('array').insert(0, ['item1', 'item2', 'item3'])
   doc.getArray('array').delete(1)
@@ -181,3 +181,28 @@ export const testDependentChanges = tc => {
   const docRestored1 = Y.createDocFromSnapshot(array1.doc, snap)
   t.compare(docRestored1.getArray('array').toArray(), ['user1item1', 'user2item1'])
 }
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testContainsUpdate = _tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const updates = []
+  ydoc.on('update', update => {
+    updates.push(update)
+  })
+  const yarr = ydoc.getArray()
+  const snapshot1 = Y.snapshot(ydoc)
+  yarr.insert(0, [1])
+  const snapshot2 = Y.snapshot(ydoc)
+  yarr.delete(0, 1)
+  const snapshotFinal = Y.snapshot(ydoc)
+  t.assert(!Y.snapshotContainsUpdate(snapshot1, updates[0]))
+  t.assert(!Y.snapshotContainsUpdate(snapshot2, updates[1]))
+  t.assert(Y.snapshotContainsUpdate(snapshot2, updates[0]))
+  t.assert(Y.snapshotContainsUpdate(snapshotFinal, updates[0]))
+  t.assert(Y.snapshotContainsUpdate(snapshotFinal, updates[1]))
+}
diff --git a/tests/testHelper.js b/tests/testHelper.js
index 8c90a099..f1ff4756 100644
--- a/tests/testHelper.js
+++ b/tests/testHelper.js
@@ -356,8 +356,9 @@ export const compare = users => {
       return true
     })
     t.compare(Y.encodeStateVector(users[i]), Y.encodeStateVector(users[i + 1]))
-    compareDS(Y.createDeleteSetFromStructStore(users[i].store), Y.createDeleteSetFromStructStore(users[i + 1].store))
+    Y.equalDeleteSets(Y.createDeleteSetFromStructStore(users[i].store), Y.createDeleteSetFromStructStore(users[i + 1].store))
     compareStructStores(users[i].store, users[i + 1].store)
+    t.compare(Y.encodeSnapshot(Y.snapshot(users[i])), Y.encodeSnapshot(Y.snapshot(users[i + 1])))
   }
   users.map(u => u.destroy())
 }
@@ -412,25 +413,6 @@ export const compareStructStores = (ss1, ss2) => {
   }
 }
 
-/**
- * @param {import('../src/internals.js').DeleteSet} ds1
- * @param {import('../src/internals.js').DeleteSet} ds2
- */
-export const compareDS = (ds1, ds2) => {
-  t.assert(ds1.clients.size === ds2.clients.size)
-  ds1.clients.forEach((deleteItems1, client) => {
-    const deleteItems2 = /** @type {Array<import('../src/internals.js').DeleteItem>} */ (ds2.clients.get(client))
-    t.assert(deleteItems2 !== undefined && deleteItems1.length === deleteItems2.length)
-    for (let i = 0; i < deleteItems1.length; i++) {
-      const di1 = deleteItems1[i]
-      const di2 = deleteItems2[i]
-      if (di1.clock !== di2.clock || di1.len !== di2.len) {
-        t.fail('DeleteSets dont match')
-      }
-    }
-  })
-}
-
 /**
  * @template T
  * @callback InitTestObjectCallback