diff --git a/cmd/tip/tip.go b/cmd/tip/tip.go
index b6cac88a..f9dad93b 100644
--- a/cmd/tip/tip.go
+++ b/cmd/tip/tip.go
@@ -45,6 +45,7 @@ func main() {
 	p := &Proxy{builder: b}
 	go p.run()
 	http.Handle("/", p)
+	http.HandleFunc("/_ah/health", p.serveHealthCheck)
 
 	if err := http.ListenAndServe(":8080", nil); err != nil {
 		p.stop()
@@ -106,6 +107,16 @@ func (p *Proxy) serveStatus(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprintf(w, "side=%v\ncurrent=%v\nerror=%v\n", p.side, p.cur, p.err)
 }
 
+func (p *Proxy) serveHealthCheck(w http.ResponseWriter, r *http.Request) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.proxy == nil {
+		http.Error(w, "not ready", 500)
+		return
+	}
+	io.WriteString(w, "ok")
+}
+
 // run runs in its own goroutine.
 func (p *Proxy) run() {
 	p.side = "a"