diff --git a/src/author.cpp b/src/author.cpp
index 6c0566dc..f8d48179 100644
--- a/src/author.cpp
+++ b/src/author.cpp
@@ -6,7 +6,7 @@
 
 #include "author.h"
 
-Author::Author(QString name, QString email, QString url, QObject *parent)
+Author::Author(const QString &name, const QString &email, const QString &url, QObject *parent)
     : QObject(parent)
     , m_name(name)
     , m_email(email)
diff --git a/src/author.h b/src/author.h
index 81eeaa54..bca834f4 100644
--- a/src/author.h
+++ b/src/author.h
@@ -18,7 +18,7 @@ class Author : public QObject
     Q_PROPERTY(QString url READ url CONSTANT)
 
 public:
-    Author(QString name, QString email, QString url, QObject *parent = nullptr);
+    Author(const QString &name, const QString &email, const QString &url, QObject *parent = nullptr);
     ~Author();
 
     QString name() const;
diff --git a/src/database.cpp b/src/database.cpp
index 0bf0d055..9dff87c2 100644
--- a/src/database.cpp
+++ b/src/database.cpp
@@ -54,7 +54,7 @@ bool Database::migrateTo1()
     return true;
 }
 
-bool Database::execute(QString query)
+bool Database::execute(const QString &query)
 {
     QSqlQuery q;
     q.prepare(query);
@@ -118,7 +118,7 @@ void Database::cleanup()
     }
 }
 
-bool Database::feedExists(QString url)
+bool Database::feedExists(const QString &url)
 {
     QSqlQuery query;
     query.prepare(QStringLiteral("SELECT COUNT (url) FROM Feeds WHERE url=:url;"));
@@ -128,7 +128,7 @@ bool Database::feedExists(QString url)
     return query.value(0).toInt() != 0;
 }
 
-void Database::addFeed(QString url)
+void Database::addFeed(const QString &url)
 {
     qDebug() << "Adding feed";
     if (feedExists(url)) {
@@ -157,7 +157,7 @@ void Database::addFeed(QString url)
     Fetcher::instance().fetch(urlFromInput.toString());
 }
 
-void Database::importFeeds(QString path)
+void Database::importFeeds(const QString &path)
 {
     QUrl url(path);
     QFile file(url.isLocalFile() ? url.toLocalFile() : url.toString());
@@ -173,7 +173,7 @@ void Database::importFeeds(QString path)
     Fetcher::instance().fetchAll();
 }
 
-void Database::exportFeeds(QString path)
+void Database::exportFeeds(const QString &path)
 {
     QUrl url(path);
     QFile file(url.isLocalFile() ? url.toLocalFile() : url.toString());
diff --git a/src/database.h b/src/database.h
index 7c0cfd7b..216bbc8c 100644
--- a/src/database.h
+++ b/src/database.h
@@ -19,13 +19,13 @@ public:
         return _instance;
     }
     bool execute(QSqlQuery &query);
-    bool execute(QString query);
-    Q_INVOKABLE void addFeed(QString url);
-    Q_INVOKABLE void importFeeds(QString path);
-    Q_INVOKABLE void exportFeeds(QString path);
+    bool execute(const QString &query);
+    Q_INVOKABLE void addFeed(const QString &url);
+    Q_INVOKABLE void importFeeds(const QString &path);
+    Q_INVOKABLE void exportFeeds(const QString &path);
 
 Q_SIGNALS:
-    void feedAdded(QString url);
+    void feedAdded(const QString &url);
 
 private:
     Database();
@@ -34,5 +34,5 @@ private:
     bool migrate();
     bool migrateTo1();
     void cleanup();
-    bool feedExists(QString url);
+    bool feedExists(const QString &url);
 };
diff --git a/src/entriesmodel.cpp b/src/entriesmodel.cpp
index cb2673fc..352682b6 100644
--- a/src/entriesmodel.cpp
+++ b/src/entriesmodel.cpp
@@ -16,7 +16,7 @@ EntriesModel::EntriesModel(Feed *feed)
     : QAbstractListModel(feed)
     , m_feed(feed)
 {
-    connect(&Fetcher::instance(), &Fetcher::feedUpdated, this, [this](QString url) {
+    connect(&Fetcher::instance(), &Fetcher::feedUpdated, this, [this](const QString &url) {
         if (m_feed->url() == url) {
             beginResetModel();
             for (auto &entry : m_entries) {
diff --git a/src/feed.cpp b/src/feed.cpp
index 08663d15..6788d3a9 100644
--- a/src/feed.cpp
+++ b/src/feed.cpp
@@ -46,12 +46,12 @@ Feed::Feed(int index)
     m_errorId = 0;
     m_errorString = QLatin1String("");
 
-    connect(&Fetcher::instance(), &Fetcher::startedFetchingFeed, this, [this](QString url) {
+    connect(&Fetcher::instance(), &Fetcher::startedFetchingFeed, this, [this](const QString &url) {
         if (url == m_url) {
             setRefreshing(true);
         }
     });
-    connect(&Fetcher::instance(), &Fetcher::feedUpdated, this, [this](QString url) {
+    connect(&Fetcher::instance(), &Fetcher::feedUpdated, this, [this](const QString &url) {
         if (url == m_url) {
             setRefreshing(false);
             Q_EMIT entryCountChanged();
@@ -60,14 +60,14 @@ Feed::Feed(int index)
             setErrorString(QLatin1String(""));
         }
     });
-    connect(&Fetcher::instance(), &Fetcher::error, this, [this](QString url, int errorId, QString errorString) {
+    connect(&Fetcher::instance(), &Fetcher::error, this, [this](const QString &url, int errorId, const QString &errorString) {
         if(url == m_url) {
             setErrorId(errorId);
             setErrorString(errorString);
             setRefreshing(false);
         }
     });
-    connect(&Fetcher::instance(), &Fetcher::imageDownloadFinished, this, [this](QString url) {
+    connect(&Fetcher::instance(), &Fetcher::imageDownloadFinished, this, [this](const QString &url) {
         if(url == m_image)
             Q_EMIT imageChanged(url);
     });
@@ -171,31 +171,31 @@ QString Feed::errorString() const
     return m_errorString;
 }
 
-void Feed::setName(QString name)
+void Feed::setName(const QString &name)
 {
     m_name = name;
     Q_EMIT nameChanged(m_name);
 }
 
-void Feed::setImage(QString image)
+void Feed::setImage(const QString &image)
 {
     m_image = image;
     Q_EMIT imageChanged(m_image);
 }
 
-void Feed::setLink(QString link)
+void Feed::setLink(const QString &link)
 {
     m_link = link;
     Q_EMIT linkChanged(m_link);
 }
 
-void Feed::setDescription(QString description)
+void Feed::setDescription(const QString &description)
 {
     m_description = description;
     Q_EMIT descriptionChanged(m_description);
 }
 
-void Feed::setAuthors(QVector<Author *> authors)
+void Feed::setAuthors(const QVector<Author *> &authors)
 {
     m_authors = authors;
     Q_EMIT authorsChanged(m_authors);
@@ -213,7 +213,7 @@ void Feed::setDeleteAfterType(int type)
     Q_EMIT deleteAfterTypeChanged(m_deleteAfterType);
 }
 
-void Feed::setLastUpdated(QDateTime lastUpdated)
+void Feed::setLastUpdated(const QDateTime &lastUpdated)
 {
     m_lastUpdated = lastUpdated;
     Q_EMIT lastUpdatedChanged(m_lastUpdated);
@@ -237,7 +237,7 @@ void Feed::setErrorId(int errorId)
     Q_EMIT errorIdChanged(m_errorId);
 }
 
-void Feed::setErrorString(QString errorString)
+void Feed::setErrorString(const QString &errorString)
 {
     m_errorString = errorString;
     Q_EMIT errorStringChanged(m_errorString);
diff --git a/src/feed.h b/src/feed.h
index ce14f8f4..9ee6269c 100644
--- a/src/feed.h
+++ b/src/feed.h
@@ -60,36 +60,36 @@ public:
 
     bool refreshing() const;
 
-    void setName(QString name);
-    void setImage(QString image);
-    void setLink(QString link);
-    void setDescription(QString description);
-    void setAuthors(QVector<Author *> authors);
+    void setName(const QString &name);
+    void setImage(const QString &image);
+    void setLink(const QString &link);
+    void setDescription(const QString &description);
+    void setAuthors(const QVector<Author *> &authors);
     void setDeleteAfterCount(int count);
     void setDeleteAfterType(int type);
-    void setLastUpdated(QDateTime lastUpdated);
+    void setLastUpdated(const QDateTime &lastUpdated);
     void setNotify(bool notify);
     void setRefreshing(bool refreshing);
     void setErrorId(int errorId);
-    void setErrorString(QString errorString);
+    void setErrorString(const QString &errorString);
 
     Q_INVOKABLE void refresh();
     void remove();
 
 Q_SIGNALS:
-    void nameChanged(QString &name);
-    void imageChanged(QString &image);
-    void linkChanged(QString &link);
-    void descriptionChanged(QString &description);
-    void authorsChanged(QVector<Author *> &authors);
+    void nameChanged(const QString &name);
+    void imageChanged(const QString &image);
+    void linkChanged(const QString &link);
+    void descriptionChanged(const QString &description);
+    void authorsChanged(const QVector<Author *> &authors);
     void deleteAfterCountChanged(int count);
     void deleteAfterTypeChanged(int type);
-    void lastUpdatedChanged(QDateTime lastUpdated);
+    void lastUpdatedChanged(const QDateTime &lastUpdated);
     void notifyChanged(bool notify);
     void entryCountChanged();
     void unreadEntryCountChanged();
     void errorIdChanged(int &errorId);
-    void errorStringChanged(QString &errorString);
+    void errorStringChanged(const QString &errorString);
 
     void refreshingChanged(bool refreshing);
 
diff --git a/src/feedsmodel.cpp b/src/feedsmodel.cpp
index 6b550ffe..01b19f06 100644
--- a/src/feedsmodel.cpp
+++ b/src/feedsmodel.cpp
@@ -21,7 +21,7 @@ FeedsModel::FeedsModel(QObject *parent)
         beginInsertRows(QModelIndex(), rowCount(QModelIndex()) - 1, rowCount(QModelIndex()) - 1);
         endInsertRows();
     });
-    connect(&Fetcher::instance(), &Fetcher::feedDetailsUpdated, this, [this](QString url, QString name, QString image, QString link, QString description, QDateTime lastUpdated) {
+    connect(&Fetcher::instance(), &Fetcher::feedDetailsUpdated, this, [this](const QString &url, const QString &name, const QString &image, const QString &link, const QString &description, const QDateTime &lastUpdated) {
         for (int i = 0; i < m_feeds.length(); i++) {
             if (m_feeds[i]->url() == url) {
                 m_feeds[i]->setName(name);
diff --git a/src/fetcher.cpp b/src/fetcher.cpp
index 6fa2ef0b..0a078e2f 100644
--- a/src/fetcher.cpp
+++ b/src/fetcher.cpp
@@ -25,7 +25,7 @@ Fetcher::Fetcher()
     manager->enableStrictTransportSecurityStore(true);
 }
 
-void Fetcher::fetch(QString url)
+void Fetcher::fetch(const QString &url)
 {
     qDebug() << "Starting to fetch" << url;
 
@@ -58,7 +58,7 @@ void Fetcher::fetchAll()
     }
 }
 
-void Fetcher::processFeed(Syndication::FeedPtr feed, QString url)
+void Fetcher::processFeed(Syndication::FeedPtr feed, const QString &url)
 {
     if (feed.isNull())
         return;
@@ -96,7 +96,7 @@ void Fetcher::processFeed(Syndication::FeedPtr feed, QString url)
     Q_EMIT feedUpdated(url);
 }
 
-void Fetcher::processEntry(Syndication::ItemPtr entry, QString url)
+void Fetcher::processEntry(Syndication::ItemPtr entry, const QString &url)
 {
     qDebug() << "Processing" << entry->title();
     QSqlQuery query;
@@ -132,7 +132,7 @@ void Fetcher::processEntry(Syndication::ItemPtr entry, QString url)
     }
 }
 
-void Fetcher::processAuthor(Syndication::PersonPtr author, QString entryId, QString url)
+void Fetcher::processAuthor(Syndication::PersonPtr author, const QString &entryId, const QString &url)
 {
     QSqlQuery query;
     query.prepare(QStringLiteral("INSERT INTO Authors VALUES(:feed, :id, :name, :uri, :email);"));
@@ -144,7 +144,7 @@ void Fetcher::processAuthor(Syndication::PersonPtr author, QString entryId, QStr
     Database::instance().execute(query);
 }
 
-void Fetcher::processEnclosure(Syndication::EnclosurePtr enclosure, Syndication::ItemPtr entry, QString feedUrl)
+void Fetcher::processEnclosure(Syndication::EnclosurePtr enclosure, Syndication::ItemPtr entry, const QString &feedUrl)
 {
     QSqlQuery query;
     query.prepare(QStringLiteral("INSERT INTO Enclosures VALUES (:feed, :id, :duration, :size, :title, :type, :url);"));
@@ -158,7 +158,7 @@ void Fetcher::processEnclosure(Syndication::EnclosurePtr enclosure, Syndication:
     Database::instance().execute(query);
 }
 
-QString Fetcher::image(QString url)
+QString Fetcher::image(const QString &url)
 {
     QString path = filePath(url);
     if (QFileInfo::exists(path)) {
@@ -170,7 +170,7 @@ QString Fetcher::image(QString url)
     return QLatin1String("");
 }
 
-void Fetcher::download(QString url)
+void Fetcher::download(const QString &url)
 {
     QNetworkRequest request((QUrl(url)));
     QNetworkReply *reply = get(request);
@@ -186,13 +186,13 @@ void Fetcher::download(QString url)
     });
 }
 
-void Fetcher::removeImage(QString url)
+void Fetcher::removeImage(const QString &url)
 {
     qDebug() << filePath(url);
     QFile(filePath(url)).remove();
 }
 
-QString Fetcher::filePath(QString url)
+QString Fetcher::filePath(const QString &url)
 {
     return QStandardPaths::writableLocation(QStandardPaths::AppDataLocation) + QStringLiteral("/") + QString::fromStdString(QCryptographicHash::hash(url.toUtf8(), QCryptographicHash::Md5).toHex().toStdString());
 }
diff --git a/src/fetcher.h b/src/fetcher.h
index fd0c2547..ea400e17 100644
--- a/src/fetcher.h
+++ b/src/fetcher.h
@@ -20,28 +20,28 @@ public:
         static Fetcher _instance;
         return _instance;
     }
-    Q_INVOKABLE void fetch(QString url);
+    Q_INVOKABLE void fetch(const QString &url);
     Q_INVOKABLE void fetchAll();
-    Q_INVOKABLE QString image(QString);
-    void removeImage(QString);
-    Q_INVOKABLE void download(QString url);
+    Q_INVOKABLE QString image(const QString &url);
+    void removeImage(const QString &url);
+    Q_INVOKABLE void download(const QString &url);
     QNetworkReply *get(QNetworkRequest &request);
 
 private:
     Fetcher();
 
-    QString filePath(QString);
-    void processFeed(Syndication::FeedPtr feed, QString url);
-    void processEntry(Syndication::ItemPtr entry, QString url);
-    void processAuthor(Syndication::PersonPtr author, QString entryId, QString url);
-    void processEnclosure(Syndication::EnclosurePtr enclosure, Syndication::ItemPtr entry, QString feedUrl);
+    QString filePath(const QString &url);
+    void processFeed(Syndication::FeedPtr feed, const QString &url);
+    void processEntry(Syndication::ItemPtr entry, const QString &url);
+    void processAuthor(Syndication::PersonPtr author, const QString &entryId, const QString &url);
+    void processEnclosure(Syndication::EnclosurePtr enclosure, Syndication::ItemPtr entry, const QString &feedUrl);
 
     QNetworkAccessManager *manager;
 
 Q_SIGNALS:
-    void startedFetchingFeed(QString url);
-    void feedUpdated(QString url);
-    void feedDetailsUpdated(QString url, QString name, QString image, QString link, QString description, QDateTime lastUpdated);
-    void error(QString url, int errorId, QString errorString);
-    void imageDownloadFinished(QString url);
+    void startedFetchingFeed(const QString &url);
+    void feedUpdated(const QString &url);
+    void feedDetailsUpdated(const QString &url, const QString &name, const QString &image, const QString &link, const QString &description, const QDateTime &lastUpdated);
+    void error(const QString &url, int errorId, const QString &errorString);
+    void imageDownloadFinished(const QString &url);
 };