diff --git a/src/main/java/de/marhali/easyi18n/ui/editor/I18nKeyAnnotator.java b/src/main/java/de/marhali/easyi18n/ui/editor/I18nKeyAnnotator.java
new file mode 100644
index 0000000..4568a1d
--- /dev/null
+++ b/src/main/java/de/marhali/easyi18n/ui/editor/I18nKeyAnnotator.java
@@ -0,0 +1,54 @@
+package de.marhali.easyi18n.ui.editor;
+
+import com.intellij.ide.DataManager;
+import com.intellij.lang.annotation.AnnotationHolder;
+import com.intellij.lang.annotation.Annotator;
+import com.intellij.lang.annotation.HighlightSeverity;
+import com.intellij.openapi.actionSystem.PlatformDataKeys;
+import com.intellij.openapi.project.Project;
+import com.intellij.psi.PsiElement;
+import com.intellij.psi.PsiLiteralValue;
+import de.marhali.easyi18n.model.LocalizedNode;
+import de.marhali.easyi18n.service.DataStore;
+import de.marhali.easyi18n.service.SettingsService;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Translation key annotator.
+ * @author marhali
+ */
+public class I18nKeyAnnotator implements Annotator {
+
+    private Project project;
+    private String previewLocale;
+
+    public I18nKeyAnnotator() {
+        DataManager.getInstance().getDataContextFromFocusAsync().onSuccess(data -> {
+            project = PlatformDataKeys.PROJECT.getData(data);
+            previewLocale = SettingsService.getInstance(project).getState().getPreviewLocale();
+        });
+    }
+
+    @Override
+    public void annotate(@NotNull PsiElement element, @NotNull AnnotationHolder holder) {
+        if(!(element instanceof PsiLiteralValue)) {
+            return;
+        }
+
+        PsiLiteralValue literalValue = (PsiLiteralValue) element;
+        String value = literalValue.getValue() instanceof String ? (String) literalValue.getValue() : null;
+
+        if(value == null) {
+            return;
+        }
+
+        LocalizedNode node = DataStore.getInstance(project).getTranslations().getNode(value);
+
+        if(node == null) { // Unknown translation. Just ignore it
+            return;
+        }
+
+        holder.newAnnotation(HighlightSeverity.INFORMATION,
+                "I18n(" + previewLocale + ": " + node.getValue().get(previewLocale) + ")").create();
+    }
+}
\ No newline at end of file
diff --git a/src/main/resources/META-INF/plugin.xml b/src/main/resources/META-INF/plugin.xml
index 348d1ac..483a1ba 100644
--- a/src/main/resources/META-INF/plugin.xml
+++ b/src/main/resources/META-INF/plugin.xml
@@ -13,5 +13,7 @@
 
         <completion.contributor language="any"
                                 implementationClass="de.marhali.easyi18n.ui.editor.I18nCompletionContributor" />
+
+        <annotator language="" implementationClass="de.marhali.easyi18n.ui.editor.I18nKeyAnnotator" />
     </extensions>
 </idea-plugin>
\ No newline at end of file