diff --git a/src/layout/LayoutLoader.cpp b/src/layout/LayoutLoader.cpp
index c1769ba..8dbe304 100644
--- a/src/layout/LayoutLoader.cpp
+++ b/src/layout/LayoutLoader.cpp
@@ -1,6 +1,7 @@
 #include "LayoutLoader.h"
 
 #include <QFile>
+#include <algorithm>
 #include <QJsonArray>
 #include <QJsonDocument>
 #include <QJsonObject>
@@ -48,6 +49,10 @@ std::optional<KeyDef> parseKey(const QJsonValue &value, QString *error)
     KeyDef key;
     if (value.isString()) {
         key.label = value.toString();
+        if (key.label.isEmpty()) {
+            *error = QStringLiteral("empty key \"\"");
+            return std::nullopt;
+        }
         return key;
     }
     if (!value.isObject()) {
@@ -104,6 +109,14 @@ std::optional<KeyDef> parseKey(const QJsonValue &value, QString *error)
         *error = QStringLiteral("modifier must be one of %1").arg(ModifierNames.join(u", "));
         return std::nullopt;
     }
+    if (key.repeat && key.type != KeyType::Keysym) {
+        *error = QStringLiteral("\"%1\": only keysym keys repeat").arg(typeName);
+        return std::nullopt;
+    }
+    if (key.stretch && (key.type == KeyType::Letters || key.type == KeyType::Keys)) {
+        *error = QStringLiteral("\"%1\" rows can't stretch; their keys come from the keymap").arg(typeName);
+        return std::nullopt;
+    }
     if (key.width <= 0) {
         *error = QStringLiteral("key \"%1\" has a non-positive width").arg(key.label);
         return std::nullopt;
@@ -197,6 +210,10 @@ std::optional<Layout> parse(const QByteArray &json, QString *error)
         auto layer = parseLayer(layerValue.toObject(), error);
         if (!layer)
             return std::nullopt;
+        if (layout.layer(layer->name)) {
+            *error = QStringLiteral("duplicate layer \"%1\"").arg(layer->name);
+            return std::nullopt;
+        }
         layout.layers.append(*layer);
     }
 
@@ -204,6 +221,10 @@ std::optional<Layout> parse(const QByteArray &json, QString *error)
         auto section = parseSection(sectionValue.toObject(), error);
         if (!section)
             return std::nullopt;
+        if (std::ranges::any_of(layout.sections, [&](const Section &s) { return s.id == section->id; })) {
+            *error = QStringLiteral("duplicate section \"%1\"").arg(section->id);
+            return std::nullopt;
+        }
         layout.sections.append(*section);
     }
 
diff --git a/tests/tst_layoutloader.cpp b/tests/tst_layoutloader.cpp
index 96670f7..7be77f1 100644
--- a/tests/tst_layoutloader.cpp
+++ b/tests/tst_layoutloader.cpp
@@ -40,6 +40,34 @@ private Q_SLOTS:
         QVERIFY(error.contains(u"warp"));
     }
 
+    void rejectsInvalidTemplates_data()
+    {
+        QTest::addColumn<QByteArray>("json");
+        QTest::addColumn<QString>("why");
+        const auto row = [](const char *key) {
+            return QByteArray(R"({"id": "t", "layers": [{"name": "l", "rows": [[)") + key + "]]}]}";
+        };
+        QTest::newRow("empty key") << row(R"("")") << u"empty"_s;
+        QTest::newRow("repeat") << row(R"({"type": "backspace", "repeat": true})") << u"repeat"_s;
+        QTest::newRow("stretch") << row(R"({"type": "letters", "row": 0, "stretch": true})") << u"stretch"_s;
+        QTest::newRow("layer twice")
+            << QByteArray(R"({"id": "t", "layers": [{"name": "l", "rows": [["a"]]}, {"name": "l", "rows": [["b"]]}]})")
+            << u"duplicate layer"_s;
+        QTest::newRow("section twice")
+            << QByteArray(R"({"id": "t", "layers": [{"name": "l", "rows": [["a"]]}], "sections": [)"
+                          R"({"id": "s", "rows": [["b"]]}, {"id": "s", "rows": [["c"]]}]})")
+            << u"duplicate section"_s;
+    }
+
+    void rejectsInvalidTemplates()
+    {
+        QFETCH(QByteArray, json);
+        QFETCH(QString, why);
+        QString error;
+        QVERIFY(!LayoutLoader::parse(json, &error));
+        QVERIFY2(error.contains(why), qPrintable(error));
+    }
+
     void rejectsMissingId()
     {
         QString error;