--- a/lib/Protobuf-PHP/library/DrSlump/Protobuf/Codec/JsonTagMap.php
+++ b/lib/Protobuf-PHP/library/DrSlump/Protobuf/Codec/JsonTagMap.php
@@ -1,1 +1,24 @@
+<?php
 
+namespace DrSlump\Protobuf\Codec;
+
+use DrSlump\Protobuf;
+
+/**
+ * This codec serializes and unserializes from/to Json strings
+ * where the keys represent the field's tag numbers.
+ *
+ * It makes use of the PhpArray codec to do the heavy work to just
+ * take care of converting the array to/from Json strings.
+ */
+class JsonTagMap extends Json
+    implements Protobuf\CodecInterface
+{
+
+    public function __construct()
+    {
+        // Setup the codec to use tag numbers as keys
+        $this->useTagNumberAsKey(true);
+    }
+}
+