diff --git a/cockatrice/src/interface/deck_sync/deck_sync_manager.cpp b/cockatrice/src/interface/deck_sync/deck_sync_manager.cpp
index 60dd34879..549b31f2c 100644
--- a/cockatrice/src/interface/deck_sync/deck_sync_manager.cpp
+++ b/cockatrice/src/interface/deck_sync/deck_sync_manager.cpp
@@ -8,9 +8,12 @@
 #include <QDirIterator>
 #include <QFile>
 #include <QFileInfo>
+#include <QFileSystemWatcher>
 #include <QSaveFile>
 #include <QStringList>
+#include <QTimer>
 #include <QUuid>
+#include <QtGlobal>
 #include <libcockatrice/deck_list/deck_diff.h>
 #include <libcockatrice/deck_list/deck_file_format.h>
 #include <libcockatrice/deck_list/deck_list.h>
@@ -19,12 +22,15 @@
 #include <libcockatrice/protocol/pb/command_deck_download.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_list.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_new_dir.pb.h>
+#include <libcockatrice/protocol/pb/command_deck_sync_check.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_upload.pb.h>
 #include <libcockatrice/protocol/pb/response.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_download.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_list.pb.h>
+#include <libcockatrice/protocol/pb/response_deck_sync_status.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_upload.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_deckstorage.pb.h>
+#include <libcockatrice/protocol/pb/serverinfo_user.pb.h>
 #include <libcockatrice/protocol/pending_command.h>
 #include <libcockatrice/utility/string_limits.h>
 
@@ -32,6 +38,7 @@ namespace
 {
 constexpr const char *SYNC_META_DIR = ".sync";
 constexpr const char *BACKUP_SUFFIX = ".sync-backup-";
+constexpr int WATCH_DEBOUNCE_MS = 2000;
 
 QString serverPathFor(const QString &relativePath)
 {
@@ -74,21 +81,145 @@ QString localPathFor(const QString &dir, const QString &name)
 
 DeckSyncManager::DeckSyncManager(QObject *parent) : QObject(parent)
 {
+    watcher = new QFileSystemWatcher(this);
+    debounceTimer = new QTimer(this);
+    debounceTimer->setSingleShot(true);
+    debounceTimer->setInterval(WATCH_DEBOUNCE_MS);
+    intervalTimer = new QTimer(this);
+    connect(watcher, &QFileSystemWatcher::fileChanged, this,
+            [this](const QString &path) { onWatchedPathChanged(path); });
+    connect(watcher, &QFileSystemWatcher::directoryChanged, this, [this](const QString &path) {
+        refreshWatcher();
+        onWatchedPathChanged(path);
+    });
+    connect(debounceTimer, &QTimer::timeout, this, &DeckSyncManager::onDebounceTimeout);
+    connect(intervalTimer, &QTimer::timeout, this, [this] { autoSyncSoon(); });
+    refreshInterval();
 }
 
 DeckSyncManager::DeckSyncManager(AbstractClient *_client, ColorIdentityProvider provider, QObject *parent)
     : QObject(parent), client(_client), colorIdentityProvider(std::move(provider))
 {
+    if (client == nullptr) {
+        return;
+    }
+    connect(
+        client, &AbstractClient::statusChanged, this,
+        [this](ClientStatus status) {
+            if (status == StatusDisconnected) {
+                offline = true;
+                debounceTimer->stop();
+            }
+        },
+        Qt::UniqueConnection);
+    connect(
+        client, &AbstractClient::userInfoChanged, this,
+        [this](const ServerInfo_User &userInfo) {
+            offline = false;
+            serverUsername = QString::fromStdString(userInfo.name());
+            autoSyncSoon();
+        },
+        Qt::UniqueConnection);
 }
 
-void DeckSyncManager::setProfile(const DeckSyncProfile &_profile)
+void DeckSyncManager::setServerIdentity(const QString &host, int port, const QString &username)
 {
-    profile = _profile;
+    serverHost = host;
+    serverPort = port;
+    serverUsername = username;
 }
 
 void DeckSyncManager::setDeckPath(const QString &path)
 {
     deckPath = path;
+    refreshWatcher();
+}
+
+void DeckSyncManager::setAutoSyncEnabled(bool enabled)
+{
+    autoSyncEnabled = enabled;
+    refreshInterval();
+}
+
+void DeckSyncManager::setSyncIntervalMinutes(int minutes)
+{
+    syncIntervalMinutes = qBound(1, minutes, 60);
+    refreshInterval();
+}
+
+DeckSyncProfile DeckSyncManager::buildProfile() const
+{
+    return DeckSyncProfile(serverHost, serverPort, serverUsername);
+}
+
+void DeckSyncManager::refreshInterval()
+{
+    intervalTimer->stop();
+    if (autoSyncEnabled) {
+        intervalTimer->start(syncIntervalMinutes * 60000);
+    }
+}
+
+void DeckSyncManager::refreshWatcher()
+{
+    watcher->removePaths(watcher->files() + watcher->directories());
+    if (deckPath.isEmpty() || !QDir(deckPath).exists()) {
+        return;
+    }
+    QStringList watched;
+    watched.append(deckPath);
+    QDirIterator it(deckPath, QDir::Dirs | QDir::Files | QDir::NoDotAndDotDot, QDirIterator::Subdirectories);
+    while (it.hasNext()) {
+        const QString path = it.next();
+        if (!path.contains("/" + QString(SYNC_META_DIR) + "/") && !path.endsWith("/" + QString(SYNC_META_DIR))) {
+            watched.append(path);
+        }
+    }
+    watcher->addPaths(watched);
+}
+
+void DeckSyncManager::onWatchedPathChanged(const QString &path)
+{
+    if (path.contains("/" + QString(SYNC_META_DIR) + "/")) {
+        return;
+    }
+    autoSyncSoon();
+}
+
+void DeckSyncManager::autoSyncSoon()
+{
+    if (!autoSyncEnabled) {
+        return;
+    }
+    debounceTimer->start(WATCH_DEBOUNCE_MS);
+}
+
+void DeckSyncManager::onDebounceTimeout()
+{
+    if (syncing) {
+        debounceTimer->start(WATCH_DEBOUNCE_MS);
+        return;
+    }
+    if (canAutoRun()) {
+        syncNow();
+    }
+}
+
+bool DeckSyncManager::canAutoRun() const
+{
+    if (!autoSyncEnabled || offline || client == nullptr || deckPath.isEmpty()) {
+        return false;
+    }
+    const DeckSyncProfile autoProfile = buildProfile();
+    if (!autoProfile.isValid()) {
+        return false;
+    }
+    const QString autoSidecarPath = DeckSyncSidecar::pathForDeckPath(deckPath, autoProfile.key());
+    if (!QFileInfo::exists(autoSidecarPath)) {
+        return false;
+    }
+    DeckSyncSidecar sidecar(autoSidecarPath);
+    return sidecar.load() && sidecar.mode == DeckSyncSidecar::MODE_LINKED;
 }
 
 void DeckSyncManager::setConflictDefault(int _conflictDefault)
@@ -96,11 +227,6 @@ void DeckSyncManager::setConflictDefault(int _conflictDefault)
     conflictDefault = _conflictDefault;
 }
 
-void DeckSyncManager::setSyncMode(DeckSyncMode mode)
-{
-    syncMode = mode;
-}
-
 bool DeckSyncManager::isSyncing() const
 {
     return syncing;
@@ -111,7 +237,8 @@ void DeckSyncManager::syncNow()
     if (syncing) {
         return;
     }
-    if (client == nullptr || !profile.isValid() || deckPath.isEmpty()) {
+    const DeckSyncProfile runProfile = buildProfile();
+    if (client == nullptr || !runProfile.isValid() || deckPath.isEmpty()) {
         emit syncFinished(SyncSummary{}, tr("Not connected to a server."));
         return;
     }
@@ -138,10 +265,11 @@ void DeckSyncManager::syncNow()
     sessionDefault = -1;
     syncMode = DeckSyncMode::TwoWay;
     firstSyncRun = false;
+    pendingServerTime = -1;
     emit syncStarted();
     emit statusMessage(tr("Scanning local decks..."));
 
-    sidecarPath = DeckSyncSidecar::pathForDeckPath(deckPath, profile.key());
+    sidecarPath = DeckSyncSidecar::pathForDeckPath(deckPath, runProfile.key());
     DeckSyncSidecar sidecar(sidecarPath);
     if (!sidecar.load()) {
         failSync(tr("Could not read sync state."));
@@ -171,12 +299,80 @@ void DeckSyncManager::syncNow()
                                                   .modified = QFileInfo(absolutePath).lastModified()});
     }
 
+    if (!firstSyncRun && sidecar.lastSyncSecs > 0) {
+        sendSyncCheck(sidecar.lastSyncSecs);
+        return;
+    }
+    fetchFullList();
+}
+
+void DeckSyncManager::fetchFullList()
+{
     Command_DeckList cmd;
     PendingCommand *pend = AbstractClient::prepareSessionCommand(cmd);
     connect(pend, &PendingCommand::finished, this, &DeckSyncManager::onListFinished);
     client->sendCommand(pend);
 }
 
+void DeckSyncManager::sendSyncCheck(qint64 lastSyncSecs)
+{
+    emit statusMessage(tr("Checking for server changes..."));
+    Command_DeckSyncCheck cmd;
+    cmd.set_last_sync_time(static_cast<google::protobuf::uint64>(lastSyncSecs));
+    PendingCommand *pend = AbstractClient::prepareSessionCommand(cmd);
+    connect(pend, &PendingCommand::finished, this, &DeckSyncManager::onCheckFinished);
+    client->sendCommand(pend);
+}
+
+void DeckSyncManager::onCheckFinished(const Response &response, const CommandContainer & /*commandContainer*/)
+{
+    if (!syncing) {
+        return;
+    }
+    if (response.response_code() != Response::RespOk) {
+        fetchFullList();
+        return;
+    }
+    const Response_DeckSyncStatus &status = response.GetExtension(Response_DeckSyncStatus::ext);
+    DeckSyncSidecar sidecar(sidecarPath);
+    if (!sidecar.load()) {
+        fetchFullList();
+        return;
+    }
+
+    bool localClean = status.changed_files_size() == 0;
+    if (localClean) {
+        for (auto it = localFiles.begin(); it != localFiles.end(); ++it) {
+            const DeckSyncRecord record = sidecar.get(it.key());
+            if (record.remoteId == -1 || record.baseHash != it.value().hash) {
+                localClean = false;
+                break;
+            }
+        }
+    }
+    if (localClean) {
+        const QMap<QString, DeckSyncRecord> knownRecords = sidecar.records();
+        for (auto it = knownRecords.begin(); it != knownRecords.end(); ++it) {
+            if (!localFiles.contains(it.key())) {
+                localClean = false;
+                break;
+            }
+        }
+    }
+    if (!localClean) {
+        if (status.changed_files_size() > 0) {
+            emit statusMessage(tr("%1 server changes, syncing...").arg(status.changed_files_size()));
+        }
+        fetchFullList();
+        return;
+    }
+
+    pendingServerTime = status.has_server_time() ? static_cast<qint64>(status.server_time()) : -1;
+    unchangedCount = localFiles.size();
+    emit statusMessage(tr("Decks are already in sync."));
+    finishSync();
+}
+
 void DeckSyncManager::collectServerFiles(const ServerInfo_DeckStorage_Folder &folder,
                                          const QString &prefix,
                                          QMap<int, ServerFile> &files,
@@ -1035,6 +1231,13 @@ void DeckSyncManager::failSync(const QString &error)
 void DeckSyncManager::finishSync()
 {
     syncing = false;
+    DeckSyncSidecar sidecar(sidecarPath);
+    if (sidecar.load()) {
+        sidecar.lastSyncSecs =
+            pendingServerTime >= 0 ? pendingServerTime : QDateTime::currentDateTime().toSecsSinceEpoch();
+        sidecar.save();
+    }
+    pendingServerTime = -1;
     const SyncSummary summary = currentSummary();
     emit statusMessage(tr("Sync complete: %1 uploaded, %2 downloaded, %3 unchanged, %4 skipped.")
                            .arg(summary.uploaded)
diff --git a/cockatrice/src/interface/deck_sync/deck_sync_manager.h b/cockatrice/src/interface/deck_sync/deck_sync_manager.h
index eecfceb7d..98c9301ac 100644
--- a/cockatrice/src/interface/deck_sync/deck_sync_manager.h
+++ b/cockatrice/src/interface/deck_sync/deck_sync_manager.h
@@ -22,6 +22,8 @@
 class AbstractClient;
 class CommandContainer;
 class DeckList;
+class QFileSystemWatcher;
+class QTimer;
 class Response;
 class ServerInfo_DeckStorage_Folder;
 
@@ -67,10 +69,11 @@ public:
     explicit DeckSyncManager(QObject *parent = nullptr);
     DeckSyncManager(AbstractClient *client, ColorIdentityProvider provider, QObject *parent = nullptr);
 
-    void setProfile(const DeckSyncProfile &_profile);
+    void setServerIdentity(const QString &host, int port, const QString &username);
     void setDeckPath(const QString &path);
     void setConflictDefault(int conflictDefault);
-    void setSyncMode(DeckSyncMode mode);
+    void setAutoSyncEnabled(bool enabled);
+    void setSyncIntervalMinutes(int minutes);
     [[nodiscard]] bool isSyncing() const;
 
 public slots:
@@ -93,6 +96,7 @@ signals:
 
 private slots:
     void onListFinished(const Response &response, const CommandContainer &commandContainer);
+    void onCheckFinished(const Response &response, const CommandContainer &commandContainer);
     void
     onEnsureDirFinished(const Response &response, const CommandContainer &commandContainer, const QVariant &extraData);
     void
@@ -158,6 +162,15 @@ private:
     void failSync(const QString &error);
     void finishSync();
     [[nodiscard]] SyncSummary currentSummary() const;
+    void fetchFullList();
+    void sendSyncCheck(qint64 lastSyncSecs);
+    void autoSyncSoon();
+    [[nodiscard]] bool canAutoRun() const;
+    void onDebounceTimeout();
+    void onWatchedPathChanged(const QString &path);
+    void refreshWatcher();
+    void refreshInterval();
+    [[nodiscard]] DeckSyncProfile buildProfile() const;
     void collectServerFiles(const ServerInfo_DeckStorage_Folder &folder,
                             const QString &prefix,
                             QMap<int, ServerFile> &files,
@@ -195,7 +208,9 @@ private:
     QString uniqueLocalPath(const QString &relativePath) const;
 
     AbstractClient *client = nullptr;
-    DeckSyncProfile profile;
+    QString serverHost;
+    int serverPort = 0;
+    QString serverUsername;
     QString deckPath;
     ColorIdentityProvider colorIdentityProvider;
     bool syncing = false;
@@ -211,6 +226,13 @@ private:
     QMap<int, ServerFile> stashedServerFiles;
     ActiveConflict activeConflict;
     DeckSyncMode syncMode = DeckSyncMode::TwoWay;
+    QFileSystemWatcher *watcher = nullptr;
+    QTimer *debounceTimer = nullptr;
+    QTimer *intervalTimer = nullptr;
+    bool autoSyncEnabled = true;
+    int syncIntervalMinutes = 5;
+    bool offline = false;
+    qint64 pendingServerTime = -1;
     int conflictDefault = DeckSyncConflictAsk;
     int sessionDefault = -1;
     bool firstSyncRun = false;
diff --git a/cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp b/cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp
index 6c5a65e73..48dfeba5a 100644
--- a/cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp
+++ b/cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp
@@ -25,6 +25,7 @@ bool DeckSyncSidecar::load()
 {
     recordMap.clear();
     mode = MODE_LINKED;
+    lastSyncSecs = 0;
 
     QFile file(filePath);
     if (!file.exists()) {
@@ -39,6 +40,7 @@ bool DeckSyncSidecar::load()
     }
     const QJsonValue modeValue = document.object().value("mode");
     mode = modeValue.isString() ? modeValue.toString() : MODE_LINKED;
+    lastSyncSecs = static_cast<qint64>(document.object().value("lastSync").toDouble());
     const QJsonObject records = document.object().value("records").toObject();
     for (auto it = records.begin(); it != records.end(); ++it) {
         if (!it.value().isObject()) {
@@ -71,6 +73,7 @@ bool DeckSyncSidecar::save() const
     QJsonObject root;
     root.insert("version", SIDECAR_FORMAT_VERSION);
     root.insert("mode", mode);
+    root.insert("lastSync", static_cast<double>(lastSyncSecs));
     root.insert("records", records);
 
     QDir().mkpath(QFileInfo(filePath).absolutePath());
diff --git a/cockatrice/src/interface/deck_sync/deck_sync_sidecar.h b/cockatrice/src/interface/deck_sync/deck_sync_sidecar.h
index 2266922bc..de746b566 100644
--- a/cockatrice/src/interface/deck_sync/deck_sync_sidecar.h
+++ b/cockatrice/src/interface/deck_sync/deck_sync_sidecar.h
@@ -35,6 +35,7 @@ public:
 
     QString filePath;           ///< Full path of the sidecar JSON file.
     QString mode = MODE_LINKED; ///< Linked normally; separate keeps this profile out of sync.
+    qint64 lastSyncSecs = 0;    ///< Last completed sync, seconds since epoch; 0 means never.
 
     explicit DeckSyncSidecar(const QString &_filePath);
 
diff --git a/cockatrice/src/interface/widgets/settings_page/general_settings_page.cpp b/cockatrice/src/interface/widgets/settings_page/general_settings_page.cpp
index 6b6678467..6a24f7db6 100644
--- a/cockatrice/src/interface/widgets/settings_page/general_settings_page.cpp
+++ b/cockatrice/src/interface/widgets/settings_page/general_settings_page.cpp
@@ -373,9 +373,22 @@ GeneralSettingsPage::GeneralSettingsPage()
         SettingsCache::instance().deckSync().setConflictDefault(conflictDefaultSelector.itemData(index).toInt());
     });
 
+    autoSyncCheckBox.setChecked(settings.deckSync().getAutoSync());
+    connect(&autoSyncCheckBox, &QCheckBox::toggled, &SettingsCache::instance().deckSync(),
+            &DeckSyncSettings::setAutoSync);
+
+    syncIntervalEdit.setMinimum(1);
+    syncIntervalEdit.setMaximum(60);
+    syncIntervalEdit.setValue(settings.deckSync().getSyncIntervalMinutes());
+    connect(&syncIntervalEdit, qOverload<int>(&QSpinBox::valueChanged), &SettingsCache::instance().deckSync(),
+            &DeckSyncSettings::setSyncIntervalMinutes);
+
     auto *deckSyncGrid = new QGridLayout;
     deckSyncGrid->addWidget(&conflictDefaultLabel, 0, 0);
     deckSyncGrid->addWidget(&conflictDefaultSelector, 0, 1);
+    deckSyncGrid->addWidget(&autoSyncCheckBox, 1, 0, 1, 2);
+    deckSyncGrid->addWidget(&syncIntervalLabel, 2, 0);
+    deckSyncGrid->addWidget(&syncIntervalEdit, 2, 1);
     deckSyncGroupBox = new QGroupBox;
     deckSyncGroupBox->setLayout(deckSyncGrid);
 
@@ -676,5 +689,8 @@ void GeneralSettingsPage::retranslateUi()
                                         tr("Keep the server deck"));
     conflictDefaultSelector.setItemText(conflictDefaultSelector.findData(DeckSyncConflictKeepNewer),
                                         tr("Keep the newer deck"));
+    autoSyncCheckBox.setText(tr("Sync decks automatically"));
+    syncIntervalLabel.setText(tr("Check every:"));
+    syncIntervalEdit.setSuffix(" " + tr("min"));
     resetAllPathsButton->setText(tr("Reset all paths"));
 }
diff --git a/cockatrice/src/interface/widgets/settings_page/general_settings_page.h b/cockatrice/src/interface/widgets/settings_page/general_settings_page.h
index 92d46c265..f410abdf2 100644
--- a/cockatrice/src/interface/widgets/settings_page/general_settings_page.h
+++ b/cockatrice/src/interface/widgets/settings_page/general_settings_page.h
@@ -108,6 +108,9 @@ private:
 
     QLabel conflictDefaultLabel;
     QComboBox conflictDefaultSelector;
+    QCheckBox autoSyncCheckBox;
+    QLabel syncIntervalLabel;
+    QSpinBox syncIntervalEdit;
 };
 
 #endif // COCKATRICE_GENERAL_SETTINGS_PAGE_H
diff --git a/cockatrice/src/interface/widgets/tabs/tab_deck_storage.cpp b/cockatrice/src/interface/widgets/tabs/tab_deck_storage.cpp
index cc68f9fc1..48111f6ea 100644
--- a/cockatrice/src/interface/widgets/tabs/tab_deck_storage.cpp
+++ b/cockatrice/src/interface/widgets/tabs/tab_deck_storage.cpp
@@ -4,7 +4,6 @@
 #include "../../deck_loader/deck_loader.h"
 #include "../../deck_sync/deck_sync_conflict.h"
 #include "../../deck_sync/deck_sync_manager.h"
-#include "../../deck_sync/deck_sync_profile.h"
 #include "../../pixel_map_generator.h"
 #include "../cards/additional_info/deck_color_identity.h"
 #include "../deck_share/deck_share_utils.h"
@@ -262,8 +261,14 @@ TabDeckStorage::TabDeckStorage(TabSupervisor *_tabSupervisor,
     syncManager = new DeckSyncManager(
         client, [](const DeckList &deck) { return getDeckColorIdentity(deck, CardDatabaseManager::query()); }, this);
     syncManager->setConflictDefault(SettingsCache::instance().deckSync().getConflictDefault());
+    syncManager->setAutoSyncEnabled(SettingsCache::instance().deckSync().getAutoSync());
+    syncManager->setSyncIntervalMinutes(SettingsCache::instance().deckSync().getSyncIntervalMinutes());
     connect(&SettingsCache::instance().deckSync(), &DeckSyncSettings::conflictDefaultChanged, syncManager,
             &DeckSyncManager::setConflictDefault);
+    connect(&SettingsCache::instance().deckSync(), &DeckSyncSettings::autoSyncChanged, syncManager,
+            &DeckSyncManager::setAutoSyncEnabled);
+    connect(&SettingsCache::instance().deckSync(), &DeckSyncSettings::syncIntervalMinutesChanged, syncManager,
+            &DeckSyncManager::setSyncIntervalMinutes);
     connect(syncManager, &DeckSyncManager::statusMessage, this, &TabDeckStorage::onSyncStatusMessage);
     connect(syncManager, &DeckSyncManager::syncFinished, this, &TabDeckStorage::onSyncFinished);
     connect(syncManager, &DeckSyncManager::firstSyncDetected, this, &TabDeckStorage::onFirstSyncDetected);
@@ -271,6 +276,7 @@ TabDeckStorage::TabDeckStorage(TabSupervisor *_tabSupervisor,
     if (currentUserInfo != nullptr) {
         syncUsername = QString::fromStdString(currentUserInfo->name());
     }
+    syncManager->setServerIdentity(client->serverName(), client->serverPort(), syncUsername);
 
     retranslateUi();
 
@@ -330,6 +336,7 @@ QString TabDeckStorage::getTargetPath() const
 void TabDeckStorage::handleConnected(const ServerInfo_User &userInfo)
 {
     syncUsername = QString::fromStdString(userInfo.name());
+    syncManager->setServerIdentity(client->serverName(), client->serverPort(), syncUsername);
     setRemoteEnabled(userInfo.user_level() & ServerInfo_User::IsRegistered);
 }
 
@@ -561,8 +568,6 @@ void TabDeckStorage::actOpenDecksFolder()
 
 void TabDeckStorage::actSyncNow()
 {
-    DeckSyncProfile profile(client->serverName(), client->serverPort(), syncUsername);
-    syncManager->setProfile(profile);
     syncManager->setDeckPath(SettingsCache::instance().paths().getDeckPath());
     aSyncNow->setEnabled(false);
     syncManager->syncNow();
diff --git a/libcockatrice_protocol/libcockatrice/protocol/pb/CMakeLists.txt b/libcockatrice_protocol/libcockatrice/protocol/pb/CMakeLists.txt
index 059e83096..0860b407b 100644
--- a/libcockatrice_protocol/libcockatrice/protocol/pb/CMakeLists.txt
+++ b/libcockatrice_protocol/libcockatrice/protocol/pb/CMakeLists.txt
@@ -26,6 +26,7 @@ set(PROTO_FILES
     command_deck_share_list.proto
     command_deck_share_list_mine.proto
     command_deck_share_remove.proto
+    command_deck_sync_check.proto
     command_deck_upload.proto
     command_del_counter.proto
     command_delete_arrow.proto
@@ -151,6 +152,7 @@ set(PROTO_FILES
     response_deck_share_download.proto
     response_deck_share_list.proto
     response_deck_share_list_mine.proto
+    response_deck_sync_status.proto
     response_deck_upload.proto
     response_dump_zone.proto
     response_forgotpasswordrequest.proto
diff --git a/libcockatrice_protocol/libcockatrice/protocol/pb/command_deck_sync_check.proto b/libcockatrice_protocol/libcockatrice/protocol/pb/command_deck_sync_check.proto
new file mode 100644
index 000000000..1afdfee42
--- /dev/null
+++ b/libcockatrice_protocol/libcockatrice/protocol/pb/command_deck_sync_check.proto
@@ -0,0 +1,11 @@
+syntax = "proto2";
+import "session_commands.proto";
+
+message Command_DeckSyncCheck {
+    extend SessionCommand {
+        optional Command_DeckSyncCheck ext = 1034;
+    }
+    // Seconds since Unix epoch of the client's last completed sync.
+    // 0 means "never synced": the server reports every stored row.
+    optional uint64 last_sync_time = 1 [default = 0];
+}
diff --git a/libcockatrice_protocol/libcockatrice/protocol/pb/response.proto b/libcockatrice_protocol/libcockatrice/protocol/pb/response.proto
index caf9febde..8ec4c3554 100644
--- a/libcockatrice_protocol/libcockatrice/protocol/pb/response.proto
+++ b/libcockatrice_protocol/libcockatrice/protocol/pb/response.proto
@@ -85,6 +85,7 @@ message Response {
         DECK_SHARE_LIST = 1104;         // Response listing shared decks
         DECK_SHARE_DOWNLOAD = 1105;     // Response for shared deck download
         DECK_SHARE_LIST_MINE = 1106;    // Response listing the caller's own shares
+        DECK_SYNC_STATUS = 1107;        // Response with changed decks since a timestamp
         CARD_ART_RULE_LIST = 1200;      // Response containing a list of card art rules
     }
 
diff --git a/libcockatrice_protocol/libcockatrice/protocol/pb/response_deck_sync_status.proto b/libcockatrice_protocol/libcockatrice/protocol/pb/response_deck_sync_status.proto
new file mode 100644
index 000000000..6d6bd2cd1
--- /dev/null
+++ b/libcockatrice_protocol/libcockatrice/protocol/pb/response_deck_sync_status.proto
@@ -0,0 +1,21 @@
+syntax = "proto2";
+import "response.proto";
+
+message DeckSyncChangedFile {
+    // Server-relative folder path without file extension, e.g. "Modern/Affinity".
+    optional string path = 1;
+    optional uint32 deck_id = 2;
+    optional string guid = 3;
+    optional string hash = 4;
+    optional uint64 last_modified = 5;
+    optional bool deleted = 6 [default = false];
+}
+
+message Response_DeckSyncStatus {
+    extend Response {
+        optional Response_DeckSyncStatus ext = 1107;
+    }
+    repeated DeckSyncChangedFile changed_files = 1;
+    // Server clock at query time; the client adopts it as its sync baseline.
+    optional uint64 server_time = 2;
+}
diff --git a/libcockatrice_protocol/libcockatrice/protocol/pb/session_commands.proto b/libcockatrice_protocol/libcockatrice/protocol/pb/session_commands.proto
index 10aefe7b5..b9a80021f 100644
--- a/libcockatrice_protocol/libcockatrice/protocol/pb/session_commands.proto
+++ b/libcockatrice_protocol/libcockatrice/protocol/pb/session_commands.proto
@@ -37,6 +37,7 @@ message SessionCommand {
         DECK_SHARE_LIST_MINE = 1032;
         DECK_SHARE_REMOVE = 1033;
         SUBMIT_PASSWORD_VERIFIER = 1034;
+        DECK_SYNC_CHECK = 1035;
         REPLAY_LIST = 1100;
         REPLAY_DOWNLOAD = 1101;
         REPLAY_MODIFY_MATCH = 1102;
diff --git a/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.cpp b/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.cpp
index 0b86d3c84..caa9ce9c6 100644
--- a/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.cpp
+++ b/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.cpp
@@ -3,6 +3,7 @@
 #include "libcockatrice/settings/settings_manager.h"
 
 #include <QVariant>
+#include <QtGlobal>
 
 DeckSyncSettings::DeckSyncSettings(const QString &settingPath, QObject *parent)
     : SettingsManager(settingPath + "deck_sync.ini", "decksync", QString(), parent)
@@ -19,3 +20,25 @@ void DeckSyncSettings::setConflictDefault(int _conflictDefault)
     setValue(_conflictDefault, "conflictDefault");
     emit conflictDefaultChanged(_conflictDefault);
 }
+
+bool DeckSyncSettings::getAutoSync() const
+{
+    return getValue("autoSync", QString(), QString(), true).toBool();
+}
+
+void DeckSyncSettings::setAutoSync(bool _autoSync)
+{
+    setValue(_autoSync, "autoSync");
+    emit autoSyncChanged(_autoSync);
+}
+
+int DeckSyncSettings::getSyncIntervalMinutes() const
+{
+    return qBound(1, getValue("syncIntervalMinutes", QString(), QString(), 5).toInt(), 60);
+}
+
+void DeckSyncSettings::setSyncIntervalMinutes(int _syncIntervalMinutes)
+{
+    setValue(_syncIntervalMinutes, "syncIntervalMinutes");
+    emit syncIntervalMinutesChanged(_syncIntervalMinutes);
+}
diff --git a/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.h b/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.h
index f984292f3..2552f52a9 100644
--- a/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.h
+++ b/libcockatrice_settings/libcockatrice/settings/deck_sync_settings.h
@@ -22,14 +22,19 @@ class DeckSyncSettings : public SettingsManager
     friend class SettingsCache;
 
 public:
+    explicit DeckSyncSettings(const QString &settingPath, QObject *parent = nullptr);
+
     [[nodiscard]] int getConflictDefault() const;
     void setConflictDefault(int _conflictDefault);
+    [[nodiscard]] bool getAutoSync() const;
+    void setAutoSync(bool _autoSync);
+    [[nodiscard]] int getSyncIntervalMinutes() const;
+    void setSyncIntervalMinutes(int _syncIntervalMinutes);
 
 signals:
     void conflictDefaultChanged(int conflictDefault);
-
-public:
-    explicit DeckSyncSettings(const QString &settingPath, QObject *parent = nullptr);
+    void autoSyncChanged(bool autoSync);
+    void syncIntervalMinutesChanged(int syncIntervalMinutes);
 
 private:
     DeckSyncSettings(const DeckSyncSettings & /*other*/);
diff --git a/servatrice/src/serversocketinterface.cpp b/servatrice/src/serversocketinterface.cpp
index e88c74527..6da45fd41 100644
--- a/servatrice/src/serversocketinterface.cpp
+++ b/servatrice/src/serversocketinterface.cpp
@@ -98,6 +98,7 @@
 #include <libcockatrice/protocol/pb/command_deck_share_list.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_share_list_mine.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_share_remove.pb.h>
+#include <libcockatrice/protocol/pb/command_deck_sync_check.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_upload.pb.h>
 #include <libcockatrice/protocol/pb/command_get_server_stats.pb.h>
 #include <libcockatrice/protocol/pb/command_replay_delete_match.pb.h>
@@ -134,6 +135,7 @@
 #include <libcockatrice/protocol/pb/response_deck_share_download.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_share_list.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_share_list_mine.pb.h>
+#include <libcockatrice/protocol/pb/response_deck_sync_status.pb.h>
 #include <libcockatrice/protocol/pb/response_deck_upload.pb.h>
 #include <libcockatrice/protocol/pb/response_forgotpasswordrequest.pb.h>
 #include <libcockatrice/protocol/pb/response_get_admin_notes.pb.h>
@@ -371,6 +373,8 @@ Response::ResponseCode AbstractServerSocketInterface::processExtendedSessionComm
             return cmdDeckUpload(cmd.GetExtension(Command_DeckUpload::ext), rc);
         case SessionCommand::DECK_DOWNLOAD:
             return cmdDeckDownload(cmd.GetExtension(Command_DeckDownload::ext), rc);
+        case SessionCommand::DECK_SYNC_CHECK:
+            return cmdDeckSyncCheck(cmd.GetExtension(Command_DeckSyncCheck::ext), rc);
         case SessionCommand::REPLAY_LIST:
             return cmdReplayList(cmd.GetExtension(Command_ReplayList::ext), rc);
         case SessionCommand::REPLAY_DOWNLOAD:
@@ -894,6 +898,80 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckSetVisibility(const
     return Response::RespOk;
 }
 
+bool AbstractServerSocketInterface::syncCheckHelper(int folderId,
+                                                    const QString &prefix,
+                                                    int userId,
+                                                    qint64 sinceSecs,
+                                                    Response_DeckSyncStatus *status)
+{
+    QSqlQuery *query = sqlInterface->prepareQuery("select id, name from {prefix}_decklist_folders where id_parent = "
+                                                  ":id_parent and id_user = :id_user");
+    query->bindValue(":id_parent", folderId);
+    query->bindValue(":id_user", userId);
+    if (!sqlInterface->execSqlQuery(query)) {
+        return false;
+    }
+    QList<std::pair<int, QString>> subfolders;
+    while (query->next()) {
+        subfolders.append({query->value(0).toInt(), query->value(1).toString()});
+    }
+    for (const auto &[subfolderId, subfolderName] : subfolders) {
+        const QString path = prefix.isEmpty() ? subfolderName : prefix + "/" + subfolderName;
+        if (!syncCheckHelper(subfolderId, path, userId, sinceSecs, status)) {
+            return false;
+        }
+    }
+
+    query = sqlInterface->prepareQuery("select id, name, guid, hash, last_modified, deleted from "
+                                       "{prefix}_decklist_files where id_folder = :id_folder and id_user = :id_user "
+                                       "and (last_modified is null or last_modified > FROM_UNIXTIME(:since))");
+    query->bindValue(":id_folder", folderId);
+    query->bindValue(":id_user", userId);
+    query->bindValue(":since", sinceSecs);
+    if (!sqlInterface->execSqlQuery(query)) {
+        return false;
+    }
+    while (query->next()) {
+        const QString name = query->value(1).toString();
+        DeckSyncChangedFile *changed = status->add_changed_files();
+        changed->set_path((prefix.isEmpty() ? name : prefix + "/" + name).toStdString());
+        changed->set_deck_id(query->value(0).toUInt());
+        changed->set_guid(query->value(2).toString().toStdString());
+        changed->set_hash(query->value(3).toString().toStdString());
+        const QDateTime lastModified = query->value(4).toDateTime();
+        if (lastModified.isValid()) {
+            changed->set_last_modified(lastModified.toSecsSinceEpoch());
+        }
+        changed->set_deleted(query->value(5).toBool());
+    }
+    return true;
+}
+
+Response::ResponseCode AbstractServerSocketInterface::cmdDeckSyncCheck(const Command_DeckSyncCheck &cmd,
+                                                                       ResponseContainer &rc)
+{
+    if (authState != PasswordRight) {
+        return Response::RespFunctionNotAllowed;
+    }
+
+    sqlInterface->checkSql();
+
+    Response_DeckSyncStatus *re = new Response_DeckSyncStatus;
+    if (!syncCheckHelper(0, QString(), userInfo->id(), static_cast<qint64>(cmd.last_sync_time()), re)) {
+        delete re;
+        return Response::RespContextError;
+    }
+
+    QSqlQuery *clockQuery = sqlInterface->prepareQuery("select unix_timestamp(now())");
+    if (!sqlInterface->execSqlQuery(clockQuery) || !clockQuery->next()) {
+        delete re;
+        return Response::RespContextError;
+    }
+    re->set_server_time(clockQuery->value(0).toULongLong());
+    rc.setResponseExtension(re);
+    return Response::RespOk;
+}
+
 Response::ResponseCode AbstractServerSocketInterface::cmdDeckDownloadPublic(const Command_DeckDownloadPublic &cmd,
                                                                             ResponseContainer &rc)
 {
diff --git a/servatrice/src/serversocketinterface.h b/servatrice/src/serversocketinterface.h
index f05fd5ac1..7a01f7c1c 100644
--- a/servatrice/src/serversocketinterface.h
+++ b/servatrice/src/serversocketinterface.h
@@ -56,6 +56,7 @@ class Command_DeckShareList;
 class Command_DeckShareListMine;
 class Command_DeckShareRemove;
 class Command_DeckShareDownload;
+class Command_DeckSyncCheck;
 class Command_ReplayList;
 class Command_ReplayDownload;
 class Command_ReplayModifyMatch;
@@ -111,6 +112,7 @@ class Command_ViewLogHistory;
 class Command_WarnUser;
 class QObject;
 class ResponseContainer;
+class Response_DeckSyncStatus;
 
 class AbstractServerSocketInterface : public Server_ProtocolHandler
 {
@@ -163,6 +165,9 @@ private:
     bool storeDeckVersion(int deckId, const QString &content, const QString &hash);
     DeckList *getDeckFromDatabase(int deckId);
     Response::ResponseCode cmdDeckDownload(const Command_DeckDownload &cmd, ResponseContainer &rc);
+    bool
+    syncCheckHelper(int folderId, const QString &prefix, int userId, qint64 sinceSecs, Response_DeckSyncStatus *status);
+    Response::ResponseCode cmdDeckSyncCheck(const Command_DeckSyncCheck &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckDownloadPublic(const Command_DeckDownloadPublic &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckShareCreate(const Command_DeckShareCreate &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckShareList(const Command_DeckShareList &cmd, ResponseContainer &rc);
diff --git a/tests/deck_sync_sidecar_test.cpp b/tests/deck_sync_sidecar_test.cpp
index 76e18d797..a86c8dc6d 100644
--- a/tests/deck_sync_sidecar_test.cpp
+++ b/tests/deck_sync_sidecar_test.cpp
@@ -125,12 +125,15 @@ TEST(DeckSyncSidecarTest, ModeRoundTripsAndDefaultsToLinked)
     ASSERT_TRUE(dir.isValid());
     DeckSyncSidecar sidecar(sidecarPath(dir));
     EXPECT_EQ(sidecar.mode, DeckSyncSidecar::MODE_LINKED);
+    EXPECT_EQ(sidecar.lastSyncSecs, 0);
     sidecar.mode = DeckSyncSidecar::MODE_SEPARATE;
+    sidecar.lastSyncSecs = 1791739200;
     EXPECT_TRUE(sidecar.save());
 
     DeckSyncSidecar reloaded(sidecarPath(dir));
     EXPECT_TRUE(reloaded.load());
     EXPECT_EQ(reloaded.mode, DeckSyncSidecar::MODE_SEPARATE);
+    EXPECT_EQ(reloaded.lastSyncSecs, 1791739200);
 }
 
 TEST(DeckSyncSidecarTest, PathForDeckPathBuildsSidecarPath)
diff --git a/tests/settings/settings_defaults_test.cpp b/tests/settings/settings_defaults_test.cpp
index 0a2fb31e0..cc8b21ecd 100644
--- a/tests/settings/settings_defaults_test.cpp
+++ b/tests/settings/settings_defaults_test.cpp
@@ -606,6 +606,33 @@ TEST_F(SettingsDefaultsTest, DeckSync_ConflictDefault_SetAndGet)
     ASSERT_EQ(s.getConflictDefault(), DeckSyncConflictAsk);
 }
 
+TEST_F(SettingsDefaultsTest, DeckSync_AutoSync_Default)
+{
+    DeckSyncSettings s(settingsPath, nullptr);
+    ASSERT_EQ(s.getAutoSync(), true);
+}
+
+TEST_F(SettingsDefaultsTest, DeckSync_AutoSync_SetAndGet)
+{
+    DeckSyncSettings s(settingsPath, nullptr);
+    s.setAutoSync(false);
+    ASSERT_EQ(s.getAutoSync(), false);
+    s.setAutoSync(true);
+    ASSERT_EQ(s.getAutoSync(), true);
+}
+
+TEST_F(SettingsDefaultsTest, DeckSync_SyncIntervalMinutes_DefaultAndBounds)
+{
+    DeckSyncSettings s(settingsPath, nullptr);
+    ASSERT_EQ(s.getSyncIntervalMinutes(), 5);
+    s.setSyncIntervalMinutes(15);
+    ASSERT_EQ(s.getSyncIntervalMinutes(), 15);
+    s.setSyncIntervalMinutes(0);
+    ASSERT_EQ(s.getSyncIntervalMinutes(), 1);
+    s.setSyncIntervalMinutes(600);
+    ASSERT_EQ(s.getSyncIntervalMinutes(), 60);
+}
+
 // --- NetworkSettings ---
 
 TEST_F(SettingsDefaultsTest, Network_ClientID_Default)