diff --git a/messages_schema.json b/messages_schema.json
index f9dec5a..fc0fc2a 100644
--- a/messages_schema.json
+++ b/messages_schema.json
@@ -1,29 +1,29 @@
 {
     "$schema": "http://json-schema.org/draft-07/schema",
     "type": "object",
+    "additionalProperties": false,
     "properties": {
         "categories": {
-            "additionalProperties": {
-                "type": "array",
-                "items": {
-                    "type": "object",
-                    "additionalProperties": false,
-                    "properties": {
-                        "category": {
-                            "type": "string"
-                        },
-                        "name": {
-                            "type": "string"
-                        }
+            "type": "array",
+            "items": {
+                "type": "object",
+                "additionalProperties": false,
+                "properties": {
+                    "category": {
+                        "type": "string"
                     },
-                    "required": [
-                        "category",
-                        "name"
-                    ]
-                }
+                    "name": {
+                        "type": "string"
+                    }
+                },
+                "required": [
+                    "category",
+                    "name"
+                ]
             }
         },
         "variables": {
+            "type": "object",
             "additionalProperties": {
                 "type": "array",
                 "items": {
@@ -48,6 +48,7 @@
             }
         },
         "messages": {
+            "type": "object",
             "additionalProperties": {
                 "type": "array",
                 "items": {
@@ -121,4 +122,4 @@
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/package.json b/package.json
index 2acc5be..e42d598 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
     "build:messages": "node -e \"fs.writeFileSync(path.join(__dirname, 'assets/js/messages.json'), JSON.stringify(require('yaml').parse(fs.readFileSync(path.join(__dirname, 'assets/messages.yml'), 'utf8'))))\"",
     "build:js": "browserify assets/js/index.js | terser > dist/bundle.js",
     "build": "npm run build:css && npm run build:messages && copyfiles index.html favicon.ico assets/**/*.* dist && npm run build:js",
-    "test:messages": "ajv validate -s messages_schema.json -d assets/js/messages.json",
+    "test:messages": "ajv validate --strict=true -s messages_schema.json -d assets/js/messages.json",
     "test": "npm run test:messages"
   },
   "repository": {