diff --git a/apps/server/src/collaboration/yjs.util.ts b/apps/server/src/collaboration/yjs.util.ts
new file mode 100644
index 00000000..3e494bbc
--- /dev/null
+++ b/apps/server/src/collaboration/yjs.util.ts
@@ -0,0 +1,177 @@
+import {
+  initProseMirrorDoc,
+  relativePositionToAbsolutePosition,
+} from 'y-prosemirror';
+import * as Y from 'yjs';
+import { Document } from '@hocuspocus/server';
+import { getSchema } from '@tiptap/core';
+import { tiptapExtensions } from './collaboration.util';
+
+export type YjsSelection = {
+  anchor: any;
+  head: any;
+};
+
+export function setYjsMark(
+  doc: Document,
+  fragment: Y.XmlFragment,
+  yjsSelection: YjsSelection,
+  markName: string,
+  markAttributes: Record<string, any>,
+) {
+  const schema = getSchema(tiptapExtensions);
+  const { mapping } = initProseMirrorDoc(fragment, schema);
+
+  // Convert JSON positions to Y.js RelativePosition objects
+  const anchorRelPos = Y.createRelativePositionFromJSON(yjsSelection.anchor);
+  const headRelPos = Y.createRelativePositionFromJSON(yjsSelection.head);
+
+  const anchor = relativePositionToAbsolutePosition(
+    doc,
+    fragment,
+    anchorRelPos,
+    mapping,
+  );
+  const head = relativePositionToAbsolutePosition(
+    doc,
+    fragment,
+    headRelPos,
+    mapping,
+  );
+
+  if (anchor === null || head === null) {
+    throw new Error(
+      'Could not resolve Y.js relative positions to absolute positions',
+    );
+  }
+
+  const from = Math.min(anchor, head);
+  const to = Math.max(anchor, head);
+
+  // Apply mark directly to Y.js XmlText nodes
+  // This bypasses updateYFragment which has compatibility issues
+  applyMarkToYFragment(fragment, from, to, markName, markAttributes);
+}
+
+function applyMarkToYFragment(
+  fragment: Y.XmlFragment,
+  from: number,
+  to: number,
+  markName: string,
+  markAttributes: Record<string, any>,
+) {
+  let pos = 0;
+
+  const processItem = (item: any): boolean => {
+    if (pos >= to) return false;
+
+    if (item instanceof Y.XmlText) {
+      const textLength = item.length;
+      const itemEnd = pos + textLength;
+
+      if (itemEnd > from && pos < to) {
+        const formatFrom = Math.max(0, from - pos);
+        const formatTo = Math.min(textLength, to - pos);
+        const formatLength = formatTo - formatFrom;
+
+        if (formatLength > 0) {
+          item.format(formatFrom, formatLength, { [markName]: markAttributes });
+        }
+      }
+      pos = itemEnd;
+    } else if (item instanceof Y.XmlElement) {
+      pos++; // Opening tag
+      for (let i = 0; i < item.length; i++) {
+        if (!processItem(item.get(i))) return false;
+      }
+      pos++; // Closing tag
+    }
+    return true;
+  };
+
+  for (let i = 0; i < fragment.length; i++) {
+    if (!processItem(fragment.get(i))) break;
+  }
+}
+
+/**
+ * Removes a mark from all text in the fragment that has the specified attribute value.
+ * Useful for deleting comments by commentId.
+ */
+export function removeYjsMarkByAttribute(
+  fragment: Y.XmlFragment,
+  markName: string,
+  attributeName: string,
+  attributeValue: string,
+) {
+  const processItem = (item: any) => {
+    if (item instanceof Y.XmlText) {
+      // Get all formatting deltas to find ranges with this mark
+      const deltas = item.toDelta();
+      let offset = 0;
+
+      for (const delta of deltas) {
+        const length = delta.insert?.length ?? 0;
+        const attributes = delta.attributes ?? {};
+        const markAttr = attributes[markName];
+
+        if (markAttr && markAttr[attributeName] === attributeValue) {
+          // Remove the mark by setting it to null
+          item.format(offset, length, { [markName]: null });
+        }
+        offset += length;
+      }
+    } else if (item instanceof Y.XmlElement) {
+      for (let i = 0; i < item.length; i++) {
+        processItem(item.get(i));
+      }
+    }
+  };
+
+  for (let i = 0; i < fragment.length; i++) {
+    processItem(fragment.get(i));
+  }
+}
+
+/**
+ * Updates a mark's attributes for all text that has the specified attribute value.
+ * Useful for resolving/unresolving comments by commentId.
+ */
+export function updateYjsMarkAttribute(
+  fragment: Y.XmlFragment,
+  markName: string,
+  findByAttribute: { name: string; value: string },
+  newAttributes: Record<string, any>,
+) {
+  const processItem = (item: any) => {
+    if (item instanceof Y.XmlText) {
+      const deltas = item.toDelta();
+      let offset = 0;
+
+      for (const delta of deltas) {
+        const length = delta.insert?.length ?? 0;
+        const attributes = delta.attributes ?? {};
+        const markAttr = attributes[markName];
+
+        if (
+          markAttr &&
+          markAttr[findByAttribute.name] === findByAttribute.value
+        ) {
+          // Update the mark with new attributes (merge with existing)
+          item.format(offset, length, {
+            [markName]: { ...markAttr, ...newAttributes },
+          });
+        }
+        offset += length;
+      }
+    } else if (item instanceof Y.XmlElement) {
+      for (let i = 0; i < item.length; i++) {
+        processItem(item.get(i));
+      }
+    }
+  };
+
+  for (let i = 0; i < fragment.length; i++) {
+    processItem(fragment.get(i));
+  }
+}