diff --git a/bun.lock b/bun.lock
index e443115..00f5bd8 100644
--- a/bun.lock
+++ b/bun.lock
@@ -11,6 +11,7 @@
         "@codemirror/legacy-modes": "^6.5.3",
         "@codemirror/lint": "^6.9.7",
         "@codemirror/lsp-client": "^6.2.5",
+        "@codemirror/merge": "^6.12.2",
         "@codemirror/state": "^6.7.1",
         "@codemirror/view": "^6.43.6",
         "@iconify/svelte": "^5.2.2",
@@ -21,6 +22,9 @@
         "@tauri-apps/plugin-opener": "^2.5.4",
         "codemirror": "^6.0.2",
         "codemirror-lang-typst": "^0.4.0",
+        "y-codemirror.next": "^0.3.5",
+        "y-websocket": "^3.0.0",
+        "yjs": "^13.6.31",
       },
       "devDependencies": {
         "@sveltejs/adapter-static": "^3.0.10",
@@ -51,6 +55,8 @@
 
     "@codemirror/lsp-client": ["@codemirror/lsp-client@6.2.5", "", { "dependencies": { "@codemirror/autocomplete": "^6.20.0", "@codemirror/language": "^6.11.0", "@codemirror/lint": "^6.8.5", "@codemirror/state": "^6.5.2", "@codemirror/view": "^6.37.0", "@lezer/highlight": "^1.2.1", "marked": "^15.0.12", "vscode-languageserver-protocol": "^3.17.5" } }, "sha512-1EqhGRmCZOV7Me+rRuwwkTuvkNoD4Nz6UcE1yx5gdwTVTLD4D9xIy48MJc0LeBQGFLn/HNRW/pHmet4EAEkJFQ=="],
 
+    "@codemirror/merge": ["@codemirror/merge@6.12.2", "", { "dependencies": { "@codemirror/language": "^6.0.0", "@codemirror/state": "^6.0.0", "@codemirror/view": "^6.17.0", "@lezer/highlight": "^1.0.0", "style-mod": "^4.1.0" } }, "sha512-V8JvyAPjHbPupqP7BeMcsdsYCbyPij74jxIbaIJDORI+VZzW44zFmon8bF+oxGWvOKhcRmkiUMXd8MxHr3YA2w=="],
+
     "@codemirror/search": ["@codemirror/search@6.7.1", "", { "dependencies": { "@codemirror/state": "^6.0.0", "@codemirror/view": "^6.37.0", "crelt": "^1.0.5" } }, "sha512-uMe5UO6PamJtSHrXhhHOzSX3ReWtiJrva6GnPMwSOrZtiExb5X5eExhr2OUZQVvdxPsKpY3Ro2mFbQadpPWmHA=="],
 
     "@codemirror/state": ["@codemirror/state@6.7.1", "", { "dependencies": { "@marijn/find-cluster-break": "^1.0.0" } }, "sha512-9QzNDgE4EYDnAHfrTlR2lwiPciiOymLtwKK+8yHQzCc7GXhAP9xdEbEJFy2IWB1j9UGUl9BsgMmTo/ImA02T7A=="],
@@ -341,10 +347,14 @@
 
     "is-reference": ["is-reference@3.0.3", "", { "dependencies": { "@types/estree": "^1.0.6" } }, "sha512-ixkJoqQvAP88E6wLydLGGqCJsrFUnqoH6HnaczB8XmDH1oaWU+xxdptvikTgaEhtZ53Ky6YXiBuUI2WXLMCwjw=="],
 
+    "isomorphic.js": ["isomorphic.js@0.2.5", "", {}, "sha512-PIeMbHqMt4DnUP3MA/Flc0HElYjMXArsw1qwJZcm9sqR8mq3l8NYizFMty0pWwE/tzIGH3EKK5+jes5mAr85yw=="],
+
     "jiti": ["jiti@2.7.0", "", { "bin": { "jiti": "lib/jiti-cli.mjs" } }, "sha512-AC/7JofJvZGrrneWNaEnJeOLUx+JlGt7tNa0wZiRPT4MY1wmfKjt2+6O2p2uz2+skll8OZZmJMNqeke7kKbNgQ=="],
 
     "kleur": ["kleur@4.1.5", "", {}, "sha512-o+NO+8WrRiQEE4/7nwRJhN1HWpVmJm511pBHUxPLtp0BUISzlBplORYSmTclCnJvQq2tKu/sgl3xVpkc7ZWuQQ=="],
 
+    "lib0": ["lib0@0.2.117", "", { "dependencies": { "isomorphic.js": "^0.2.4" }, "bin": { "0serve": "bin/0serve.js", "0gentesthtml": "bin/gentesthtml.js", "0ecdsa-generate-keypair": "bin/0ecdsa-generate-keypair.js" } }, "sha512-DeXj9X5xDCjgKLU/7RR+/HQEVzuuEUiwldwOGsHK/sfAfELGWEyTcf0x+uOvCvK3O2zPmZePXWL85vtia6GyZw=="],
+
     "lightningcss": ["lightningcss@1.32.0", "", { "dependencies": { "detect-libc": "^2.0.3" }, "optionalDependencies": { "lightningcss-android-arm64": "1.32.0", "lightningcss-darwin-arm64": "1.32.0", "lightningcss-darwin-x64": "1.32.0", "lightningcss-freebsd-x64": "1.32.0", "lightningcss-linux-arm-gnueabihf": "1.32.0", "lightningcss-linux-arm64-gnu": "1.32.0", "lightningcss-linux-arm64-musl": "1.32.0", "lightningcss-linux-x64-gnu": "1.32.0", "lightningcss-linux-x64-musl": "1.32.0", "lightningcss-win32-arm64-msvc": "1.32.0", "lightningcss-win32-x64-msvc": "1.32.0" } }, "sha512-NXYBzinNrblfraPGyrbPoD19C1h9lfI/1mzgWYvXUTe414Gz/X1FD2XBZSZM7rRTrMA8JL3OtAaGifrIKhQ5yQ=="],
 
     "lightningcss-android-arm64": ["lightningcss-android-arm64@1.32.0", "", { "os": "android", "cpu": "arm64" }, "sha512-YK7/ClTt4kAK0vo6w3X+Pnm0D2cf2vPHbhOXdoNti1Ga0al1P4TBZhwjATvjNwLEBCnKvjJc2jQgHXH0NEwlAg=="],
@@ -435,6 +445,14 @@
 
     "w3c-keyname": ["w3c-keyname@2.2.8", "", {}, "sha512-dpojBhNsCNN7T82Tm7k26A6G9ML3NkhDsnw9n/eoxSRlVBB4CEtIQ/KTCLI2Fwf3ataSXRhYFkQi3SlnFwPvPQ=="],
 
+    "y-codemirror.next": ["y-codemirror.next@0.3.5", "", { "dependencies": { "lib0": "^0.2.42" }, "peerDependencies": { "@codemirror/state": "^6.0.0", "@codemirror/view": "^6.0.0", "yjs": "^13.5.6" } }, "sha512-VluNu3e5HfEXybnypnsGwKAj+fKLd4iAnR7JuX1Sfyydmn1jCBS5wwEL/uS04Ch2ib0DnMAOF6ZRR/8kK3wyGw=="],
+
+    "y-protocols": ["y-protocols@1.0.7", "", { "dependencies": { "lib0": "^0.2.85" }, "peerDependencies": { "yjs": "^13.0.0" } }, "sha512-YSVsLoXxO67J6eE/nV4AtFtT3QEotZf5sK5BHxFBXso7VDUT3Tx07IfA6hsu5Q5OmBdMkQVmFZ9QOA7fikWvnw=="],
+
+    "y-websocket": ["y-websocket@3.0.0", "", { "dependencies": { "lib0": "^0.2.102", "y-protocols": "^1.0.5" }, "peerDependencies": { "yjs": "^13.5.6" } }, "sha512-mUHy7AzkOZ834T/7piqtlA8Yk6AchqKqcrCXjKW8J1w2lPtRDjz8W5/CvXz9higKAHgKRKqpI3T33YkRFLkPtg=="],
+
+    "yjs": ["yjs@13.6.31", "", { "dependencies": { "lib0": "^0.2.99" } }, "sha512-Eq+5BRfbeGyqGVrTJL3bEcr8gKkxPuyuoHmAwpk52fDb8kOVMrfVSTRPd6yiGgX5Fskb96qCRjzjbRjrL4YEnw=="],
+
     "zimmerframe": ["zimmerframe@1.1.4", "", {}, "sha512-B58NGBEoc8Y9MWWCQGl/gq9xBCe4IiKM0a2x7GZdQKOW5Exr8S1W24J6OgM1njK8xCRGvAJIL/MxXHf6SkmQKQ=="],
 
     "@tailwindcss/oxide-wasm32-wasi/@emnapi/core": ["@emnapi/core@1.11.2", "", { "dependencies": { "@emnapi/wasi-threads": "1.2.2", "tslib": "^2.4.0" }, "bundled": true }, "sha512-TC8MkTuZUtcTSiFeuC0ksCh9QIJ5+F21MvZ4Wn4ORfYaFJ/0dsiudv5tVkejgwZlwQ39jL9WWDe2lz8x0WglOA=="],
diff --git a/package.json b/package.json
index 12b73d5..62ae2db 100644
--- a/package.json
+++ b/package.json
@@ -20,6 +20,7 @@
     "@codemirror/legacy-modes": "^6.5.3",
     "@codemirror/lint": "^6.9.7",
     "@codemirror/lsp-client": "^6.2.5",
+    "@codemirror/merge": "^6.12.2",
     "@codemirror/state": "^6.7.1",
     "@codemirror/view": "^6.43.6",
     "@iconify/svelte": "^5.2.2",
@@ -29,7 +30,10 @@
     "@tauri-apps/plugin-dialog": "^2.7.2",
     "@tauri-apps/plugin-opener": "^2.5.4",
     "codemirror": "^6.0.2",
-    "codemirror-lang-typst": "^0.4.0"
+    "codemirror-lang-typst": "^0.4.0",
+    "y-codemirror.next": "^0.3.5",
+    "y-websocket": "^3.0.0",
+    "yjs": "^13.6.31"
   },
   "devDependencies": {
     "@sveltejs/adapter-static": "^3.0.10",
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 1ae1119..0ece8c5 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -1062,6 +1062,32 @@ fn cloud_sync_document(
     sync::sync_document(&server_url, &token, &app, &store, &path)
 }
 
+#[tauri::command]
+fn cloud_room_id(
+    app: AppHandle,
+    store: State<'_, Store>,
+    path: String,
+    file: String,
+) -> Result<Option<String>, String> {
+    if let Some(link) = store.document_link(&path)? {
+        return Ok(Some(link.document_id));
+    }
+
+    let meta = store.meta(&path)?;
+    let Some(cloud_project_id) = meta.cloud_project_id else {
+        return Ok(None);
+    };
+
+    let (server_url, token) = cloud_credentials(&app, &store)?;
+    let manifest = sync::get_manifest(&server_url, &token, &cloud_project_id)?;
+
+    Ok(manifest
+        .files
+        .into_iter()
+        .find(|entry| entry.path == file)
+        .map(|entry| format!("project:{}:{}", cloud_project_id, entry.id)))
+}
+
 #[tauri::command]
 fn cloud_resolve_document(
     app: AppHandle,
@@ -1425,6 +1451,7 @@ pub fn run() {
             cloud_download_document,
             cloud_delete_document,
             cloud_sync_document,
+            cloud_room_id,
             cloud_resolve_document,
             cloud_document_link,
             cloud_linked_documents,
diff --git a/src-tauri/src/sync.rs b/src-tauri/src/sync.rs
index 0c0731b..6d4b64e 100644
--- a/src-tauri/src/sync.rs
+++ b/src-tauri/src/sync.rs
@@ -241,6 +241,7 @@ pub fn move_cloud_project(
 
 #[derive(Deserialize)]
 pub struct ManifestEntry {
+    pub id: String,
     pub path: String,
     pub hash: String,
 }
diff --git a/src/lib/components/ConflictModal.svelte b/src/lib/components/ConflictModal.svelte
index bbb90cc..04e73e0 100644
--- a/src/lib/components/ConflictModal.svelte
+++ b/src/lib/components/ConflictModal.svelte
@@ -1,5 +1,9 @@
 <script lang="ts">
+  import { onDestroy } from "svelte";
   import Icon from "@iconify/svelte";
+  import { EditorView } from "@codemirror/view";
+  import { EditorState } from "@codemirror/state";
+  import { MergeView } from "@codemirror/merge";
   import Modal from "./Modal.svelte";
   import type { Conflict, Resolution } from "$lib/ts/api";
 
@@ -25,6 +29,37 @@
 
   const current = $derived(conflicts[index]);
 
+  let diffHost: HTMLDivElement | undefined = $state();
+  let mergeView: MergeView | null = null;
+
+  function readOnlyState(doc: string) {
+    return EditorState.create({
+      doc,
+      extensions: [EditorView.editable.of(false), EditorView.lineWrapping],
+    });
+  }
+
+  $effect(() => {
+    const conflict = current;
+    mergeView?.destroy();
+    mergeView = null;
+
+    if (!diffHost || !conflict || conflict.binary) return;
+
+    mergeView = new MergeView({
+      a: readOnlyState(conflict.local_text),
+      b: readOnlyState(conflict.remote_text),
+      parent: diffHost,
+      gutter: true,
+      highlightChanges: true,
+      collapseUnchanged: {},
+    });
+  });
+
+  onDestroy(() => {
+    mergeView?.destroy();
+  });
+
   function choose(option: "merged" | "local" | "remote") {
     mode[index] = option;
     choices[index] =
@@ -97,6 +132,17 @@
           </p>
         </div>
       {:else}
+        <div class="flex flex-col gap-1">
+          <div class="flex justify-between text-[10px] text-[var(--color-ink-muted)]">
+            <span>This device</span>
+            <span>Cloud</span>
+          </div>
+          <div
+            class="scroll-thin h-64 w-full overflow-auto rounded-md border border-[var(--color-line)] text-xs"
+            bind:this={diffHost}
+          ></div>
+        </div>
+
         <div class="flex items-center gap-1.5">
           {#each [["merged", "Merged"], ["local", "This device"], ["remote", "Cloud"]] as [option, label]}
             <button
diff --git a/src/lib/components/Editor.svelte b/src/lib/components/Editor.svelte
index 7338caa..74c3503 100644
--- a/src/lib/components/Editor.svelte
+++ b/src/lib/components/Editor.svelte
@@ -28,6 +28,9 @@
   } from "@codemirror/autocomplete";
   import { lintGutter, setDiagnostics } from "@codemirror/lint";
   import { LSPClient, languageServerExtensions } from "@codemirror/lsp-client";
+  import { yCollab } from "y-codemirror.next";
+  import type { Awareness } from "y-protocols/awareness";
+  import type * as Y from "yjs";
 
   import { typstCompletions } from "$lib/ts/completions";
   import { editorTheme } from "$lib/ts/editor-theme";
@@ -41,6 +44,7 @@
     targetPath: string;
     enableLsp?: boolean;
     diagnostics?: Diagnostic[];
+    collab?: { text: Y.Text; awareness: Awareness } | null;
     onchange: (value: string) => void;
     onsave: () => void;
     onlspstatus?: (status: "off" | "starting" | "on" | "unavailable") => void;
@@ -53,6 +57,7 @@
     targetPath,
     enableLsp = true,
     diagnostics = [],
+    collab = null,
     onchange,
     onsave,
     onlspstatus,
@@ -65,6 +70,7 @@
   const languageSlot = new Compartment();
   const lspSlot = new Compartment();
   const themeSlot = new Compartment();
+  const collabSlot = new Compartment();
 
   const bridge = new LspBridge();
   let client: LSPClient | null = null;
@@ -158,6 +164,7 @@
           languageSlot.of(isToml ? StreamLanguage.define(toml) : []),
           lspSlot.of([]),
           themeSlot.of(editorTheme(app.theme === "dark")),
+          collabSlot.of([]),
           ...(isToml
             ? []
             : [autocompletion({ override: [typstCompletions] })]),
@@ -209,9 +216,34 @@
     });
   }
 
+  let boundCollab: { text: Y.Text; awareness: Awareness } | null = null;
+
+  $effect(() => {
+    const next = collab;
+    if (next === boundCollab) return;
+
+    laterDispatch((current) => {
+      if (next) {
+        current.dispatch({
+          changes: {
+            from: 0,
+            to: current.state.doc.length,
+            insert: next.text.toString(),
+          },
+          effects: collabSlot.reconfigure([
+            yCollab(next.text, next.awareness),
+          ]),
+        });
+      } else {
+        current.dispatch({ effects: collabSlot.reconfigure([]) });
+      }
+      boundCollab = next;
+    });
+  });
+
   $effect(() => {
     const next = content;
-    if (!view) return;
+    if (!view || collab) return;
     if (view.state.doc.toString() === next) return;
 
     laterDispatch((current) => {
diff --git a/src/lib/ts/api.ts b/src/lib/ts/api.ts
index d1bdd35..b9e7682 100644
--- a/src/lib/ts/api.ts
+++ b/src/lib/ts/api.ts
@@ -404,6 +404,9 @@ export const cloudNewDocument = (title: string, folderId?: string | null) =>
 export const cloudSyncDocument = (path: string) =>
   invoke<SyncReport>("cloud_sync_document", { path });
 
+export const cloudRoomId = (path: string, file: string) =>
+  invoke<string | null>("cloud_room_id", { path, file });
+
 export const cloudResolveDocument = (
   path: string,
   content: string,
diff --git a/src/lib/ts/state.svelte.ts b/src/lib/ts/state.svelte.ts
index 2dead66..4e31d90 100644
--- a/src/lib/ts/state.svelte.ts
+++ b/src/lib/ts/state.svelte.ts
@@ -1,5 +1,10 @@
 import { listen } from "@tauri-apps/api/event";
 import * as api from "./api";
+import {
+  openCollabSession,
+  closeCollabSession,
+  type CollabSession,
+} from "./yjs-client";
 import type {
   Account,
   BrowseEntry,
@@ -67,6 +72,10 @@ interface AppState {
   download: DownloadProgress | null;
   syncing: boolean;
   conflicts: Conflict[];
+  collab: CollabSession | null;
+  collabIntent: boolean;
+  collabStatus: "connecting" | "connected" | "offline" | null;
+  collabConflict: Conflict | null;
   status: string;
   error: string;
   theme: "light" | "dark";
@@ -111,6 +120,10 @@ export const app = $state<AppState>({
   download: null,
   syncing: false,
   conflicts: [],
+  collab: null,
+  collabIntent: false,
+  collabStatus: null,
+  collabConflict: null,
   status: "",
   error: "",
   theme: "light",
@@ -382,6 +395,7 @@ function handleDeviceEvent(event: DeviceEvent) {
       event.document_id === linkedDocument);
 
   if (matchesOpenTarget) {
+    if (app.collabIntent) return;
     autoSync();
   } else if (app.scope === "cloud") {
     refreshCloud();
@@ -587,10 +601,19 @@ export async function openTarget(path: string) {
   }
 }
 
+function stopCollab() {
+  closeCollabSession(app.collab);
+  app.collab = null;
+  app.collabIntent = false;
+  app.collabStatus = null;
+  app.collabConflict = null;
+}
+
 export async function closeTarget() {
   cancelScheduledCompile();
   cancelAutosave();
   if (app.dirty) await saveActiveFile();
+  stopCollab();
   app.view = "files";
   app.target = null;
   app.activePath = null;
@@ -617,6 +640,7 @@ export async function openFile(file: string) {
   cancelAutosave();
 
   if (app.dirty && app.activePath) await saveActiveFile();
+  stopCollab();
 
   try {
     const payload = await api.readTargetFile(app.target.path, file);
@@ -624,11 +648,100 @@ export async function openFile(file: string) {
     app.editorContent = payload.is_text ? payload.content : "";
     app.dirty = false;
     if (payload.is_text) await compile();
+    if (payload.is_text) await tryOpenCollab(file, app.editorContent);
   } catch (error) {
     setError(error);
   }
 }
 
+function bindCollabSession(session: CollabSession) {
+  app.collab = session;
+  app.collabStatus = session.provider.wsconnected ? "connected" : "connecting";
+  session.provider.on("status", (event: { status: string }) => {
+    app.collabStatus =
+      event.status === "connected"
+        ? "connected"
+        : event.status === "connecting"
+          ? "connecting"
+          : "offline";
+  });
+}
+
+async function tryOpenCollab(file: string, diskContent: string) {
+  if (!app.target || !app.settings?.device_token) return;
+
+  let roomId: string | null;
+  try {
+    roomId = await api.cloudRoomId(app.target.path, file);
+  } catch {
+    roomId = null;
+  }
+  if (!roomId) return;
+
+  app.collabIntent = true;
+  app.collabStatus = "connecting";
+
+  const session = openCollabSession(
+    app.settings.server_url,
+    app.settings.device_token,
+    roomId,
+  );
+
+  const synced = await new Promise<boolean>((resolve) => {
+    session.provider.once("synced", (isSynced: boolean) => resolve(isSynced));
+  }).catch(() => false);
+
+  if (app.activePath !== file) {
+    closeCollabSession(session);
+    return;
+  }
+
+  if (!synced) {
+    bindCollabSession(session);
+    return;
+  }
+
+  const remoteText = session.text.toString();
+  if (remoteText !== diskContent) {
+    app.collabConflict = {
+      path: file,
+      local_text: diskContent,
+      remote_text: remoteText,
+      merged_text: remoteText,
+      server_hash: "",
+      auto_merged: false,
+      binary: false,
+    };
+    pendingCollabSession = session;
+    return;
+  }
+
+  bindCollabSession(session);
+}
+
+let pendingCollabSession: CollabSession | null = null;
+
+export function resolveCollabConflict(content: string) {
+  const session = pendingCollabSession;
+  pendingCollabSession = null;
+  app.collabConflict = null;
+  if (!session) return;
+
+  const ytext = session.text;
+  ytext.doc?.transact(() => {
+    ytext.delete(0, ytext.length);
+    ytext.insert(0, content);
+  });
+
+  bindCollabSession(session);
+}
+
+export function cancelCollabConflict() {
+  closeCollabSession(pendingCollabSession);
+  pendingCollabSession = null;
+  app.collabConflict = null;
+}
+
 export async function saveActiveFile() {
   if (!app.target || !app.activePath) return;
   try {
@@ -711,9 +824,14 @@ export function cancelScheduledCompile() {
 
 let autosaveTimer: ReturnType<typeof setTimeout> | null = null;
 
+const COLLAB_AUTOSAVE_SECONDS = 5;
+
 export function scheduleAutosave() {
-  const seconds = app.settings?.autosave_seconds ?? 0;
   if (autosaveTimer) clearTimeout(autosaveTimer);
+
+  const seconds = app.collabIntent
+    ? Math.min(app.settings?.autosave_seconds || COLLAB_AUTOSAVE_SECONDS, COLLAB_AUTOSAVE_SECONDS)
+    : (app.settings?.autosave_seconds ?? 0);
   if (seconds <= 0) return;
 
   autosaveTimer = setTimeout(() => {
diff --git a/src/lib/ts/yjs-client.ts b/src/lib/ts/yjs-client.ts
new file mode 100644
index 0000000..502645f
--- /dev/null
+++ b/src/lib/ts/yjs-client.ts
@@ -0,0 +1,38 @@
+import * as Y from "yjs";
+import { WebsocketProvider } from "y-websocket";
+
+export interface CollabSession {
+  doc: Y.Doc;
+  text: Y.Text;
+  provider: WebsocketProvider;
+}
+
+function wsUrl(serverUrl: string) {
+  return serverUrl
+    .replace(/^https:/, "wss:")
+    .replace(/^http:/, "ws:")
+    .replace(/\/$/, "");
+}
+
+export function openCollabSession(
+  serverUrl: string,
+  deviceToken: string,
+  roomId: string,
+): CollabSession {
+  const doc = new Y.Doc();
+  const text = doc.getText("typst");
+
+  const provider = new WebsocketProvider(`${wsUrl(serverUrl)}/yjs`, roomId, doc, {
+    params: { token: deviceToken },
+    disableBc: true,
+  });
+
+  return { doc, text, provider };
+}
+
+export function closeCollabSession(session: CollabSession | null) {
+  if (!session) return;
+  session.provider.disconnect();
+  session.provider.destroy();
+  session.doc.destroy();
+}