diff --git a/_content/css/styles.css b/_content/css/styles.css
index 1774461..7e824f2 100644
--- a/_content/css/styles.css
+++ b/_content/css/styles.css
@@ -59,6 +59,7 @@
   --color-text-link: var(--turq-dark);
   --color-text-subtle: var(--gray-4);
   --color-text-inverted: var(--white);
+  --color-text-alert: #aa536c;
   --color-code-comment: var(--green);
 
   /* Interactive Colors */
@@ -102,6 +103,7 @@
   --color-text: var(--gray-9);
   --color-text-link: var(--turq-med);
   --color-text-subtle: var(--gray-7);
+  --color-text-alert: #e67193;
   --color-code-comment: var(--green-light);
 }
 @media (prefers-color-scheme: dark) {
@@ -131,6 +133,7 @@
     --color-text: var(--gray-9);
     --color-text-link: var(--turq-med);
     --color-text-subtle: var(--gray-7);
+    --color-text-alert: #e67193;
     --color-code-comment: var(--green-light);
   }
 }
@@ -4574,6 +4577,12 @@
   padding: 0;
   border-radius: 0;
 }
+.Playground-output .stderr {
+  color: var(--color-text-alert);
+}
+.Playground-output .system {
+  color: var(--color-text-subtle);
+}
 .Playground-inputContainer,
 .Playground-input {
   background: var(--color-background-playground-input);
@@ -4886,12 +4895,16 @@
 div.play .buttons .Button {
   margin-left: 0.3125rem;
 }
+
+/* TODO(rsc): are these selectors stale? It looks like they were not ported to go.dev/play.
+ * See for example .Playground-output .stderr. */
 .output .stderr {
   color: #933;
 }
 .output .system {
   color: #999;
 }
+
 .permalink {
   display: none;
 }
diff --git a/_content/js/playground.js b/_content/js/playground.js
index 06204c7..b23054c 100644
--- a/_content/js/playground.js
+++ b/_content/js/playground.js
@@ -50,12 +50,17 @@
     // Backwards compatibility: default values do not affect the output.
     var events = data.Events || [];
     var errors = data.Errors || '';
+    var vetErrors = data.VetErrors || '';
     var status = data.Status || 0;
     var isTest = data.IsTest || false;
     var testsFailed = data.TestsFailed || 0;
 
     var timeout;
     output({ Kind: 'start' });
+    if (vetErrors !== '') {
+      output({ Kind: 'stderr', Body: vetErrors });
+      output({ Kind: 'system', Body: '\nGo vet failed.\n\n' });
+    }
     function next() {
       if (!events || events.length === 0) {
         if (isTest) {
diff --git a/internal/play/proxy.go b/internal/play/proxy.go
index 60047ec..f896ef9 100644
--- a/internal/play/proxy.go
+++ b/internal/play/proxy.go
@@ -23,12 +23,14 @@
 const playgroundURL = "https://play.golang.org"
 
 type Request struct {
-	Body string
+	Body    string
+	WithVet bool
 }
 
 type Response struct {
-	Errors string
-	Events []Event
+	Errors    string
+	Events    []Event
+	VetErrors string
 }
 
 type Event struct {
@@ -62,8 +64,9 @@
 	ctx := r.Context()
 
 	body := r.FormValue("body")
+	withVet := r.FormValue("withVet")
 	res := &Response{}
-	req := &Request{Body: body}
+	req := &Request{Body: body, WithVet: withVet == "true"}
 	if err := makeCompileRequest(ctx, backend(r), req, res); err != nil {
 		log.Printf("ERROR compile error %s: %v", backend(r), err)
 		http.Error(w, "Internal Server Error", http.StatusInternalServerError)