diff --git a/lib/index.js b/lib/index.js
index <HASH>..<HASH> 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -12,6 +12,12 @@
 /* eslint-env commonjs */
 
 /*
+ * Constants.
+ */
+
+var SOURCE = 'remark-lint';
+
+/*
  * Dependencies.
  */
 
@@ -100,6 +106,7 @@ function attachFactory(id, rule, options) {
 
                 while (scope.index < messages.length) {
                     messages[scope.index].ruleId = id;
+                    messages[scope.index].source = SOURCE;
 
                     scope.index++;
                 }
Add `source` property on exposed `VFile` messages

This paves the way for externalising the `filter` functionality.