diff --git a/tools/runner/index.html b/tools/runner/index.html
index 6c9a8affed58c2..9bc0dec6890bff 100644
--- a/tools/runner/index.html
+++ b/tools/runner/index.html
@@ -8,7 +8,6 @@
 <script src='/common/get-host-info.sub.js'></script>
 <script src='runner.js'></script>
 
-
 <header class="navbar navbar-inverse navbar-fixed-top">
   <div class="container">
     <div class="navbar-header">
@@ -21,6 +20,13 @@
 </header>
 
 <div class="container">
+  <div class="alert alert-warning">
+        This runner does not fully support all test types and has a number of
+        <a href="https://github.com/web-platform-tests/wpt/labels/runner">known issues</a>.
+        <code>./wpt run</code> is a more well-supported runner, see the documentation on
+        <a href="https://web-platform-tests.org/running-tests/">running tests</a>.
+  </div>
+
   <div id="testControl" class="panel panel-default">
     <div class="panel-body">
       <form id='options' class='horizontal-form' onsubmit='return false;'>