diff --git a/validator/webui/@polymer/webui-mainpage/webui-mainpage.html b/validator/webui/@polymer/webui-mainpage/webui-mainpage.html
index 3782f97198a6..00b225de19b9 100644
--- a/validator/webui/@polymer/webui-mainpage/webui-mainpage.html
+++ b/validator/webui/@polymer/webui-mainpage/webui-mainpage.html
@@ -298,9 +298,17 @@
 
         // Interprets the parameters after the '#' in the URL.
         var params = getLocationHashParams();
+        // Extracts the code to be validated if sent as a query param.
+        const incomingDocStr = getIncomingDoc(params);
+        if (incomingDocStr) {
+          editor.setEditorValue(incomingDocStr);
+          const format = params['htmlFormat'] || 'AMP';
+          urlForm.setHtmlFormat(format)
+        }
+
         // If #url=<url> was provided, load it, otherwise, start with the
         // minimum valid AMP document.
-        if (params.hasOwnProperty('url') && params['url']) {
+        else if (params.hasOwnProperty('url') && params['url']) {
           this.$.urlForm.setURLAndValidate(params['url']);
           // If filter=<error_category> was provided, filter error-list.
           if (params.hasOwnProperty('filter') && params['filter']) {
diff --git a/validator/webui/serve-standalone.go b/validator/webui/serve-standalone.go
index ab8bb6ab4d70..387a0d46459e 100644
--- a/validator/webui/serve-standalone.go
+++ b/validator/webui/serve-standalone.go
@@ -46,7 +46,7 @@ func handler(w http.ResponseWriter, r *http.Request) {
 		//
 		// Handle '/'.
 		//
-		if r.RequestURI == "/" {
+		if r.URL.Path == "/" {
 			bytes, err := ioutil.ReadFile("index.html")
 			if err != nil {
 				http.Error(w, "File not found.", http.StatusNotFound)
diff --git a/validator/webui/webui.js b/validator/webui/webui.js
index 93b97fb17f6c..33753a0c3749 100644
--- a/validator/webui/webui.js
+++ b/validator/webui/webui.js
@@ -15,6 +15,8 @@
  * limitations under the license.
  */
 
+const DOC_INPUT_ATTR = 'doc';
+
 // Extracts a dictionary of parameters from window.location.hash.
 function getLocationHashParams() {
   const paramStrings = window.location.hash.substr(1).split('&');
@@ -46,3 +48,17 @@ function setLocationHashParams(params) {
   }
   window.location.hash = out.join('&');
 }
+
+// Base64 encoded ascii to ucs-2 string.
+function atou(str) {
+  return decodeURIComponent(escape(atob(str)));
+}
+
+// Get query param that may contain an encoded document to be validated. Decode
+// and return.
+function getIncomingDoc(params) {
+  if (!params || !params[DOC_INPUT_ATTR]) {
+    return null;
+  }
+  return atou(params[DOC_INPUT_ATTR]);
+}