diff --git a/bridges/gui_bridge.py b/bridges/gui_bridge.py
index 3137770..d72aa96 100644
--- a/bridges/gui_bridge.py
+++ b/bridges/gui_bridge.py
@@ -19,10 +19,10 @@ import subprocess
 import sys
 import threading
 import tkinter as tk
-from tkinter import filedialog, messagebox, scrolledtext
+from tkinter import filedialog, messagebox, scrolledtext, simpledialog
 
 SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
-BRIDGE_PATH = os.path.join(SCRIPT_DIR, "s3_bridge.py")
+BRIDGE_PATH = os.path.join(SCRIPT_DIR, "s3-bridge", "s3_bridge.py")
 
 
 class BridgeGUI(tk.Tk):
@@ -74,6 +74,8 @@ class BridgeGUI(tk.Tk):
 
         tk.Button(self, text="Start", command=self.start_bridge, width=12).grid(row=5, column=0, columnspan=2, **pad)
         tk.Button(self, text="Stop", command=self.stop_bridge, width=12).grid(row=5, column=2, columnspan=2, **pad)
+        self.mark_btn = tk.Button(self, text="Add Mark", command=self.add_mark, width=12, state="disabled")
+        self.mark_btn.grid(row=5, column=4, **pad)
 
         # Row 6: Log view
         self.log_view = scrolledtext.ScrolledText(self, height=20, width=90, state="disabled")
@@ -135,6 +137,7 @@ class BridgeGUI(tk.Tk):
                 args,
                 stdout=subprocess.PIPE,
                 stderr=subprocess.STDOUT,
+                stdin=subprocess.PIPE,
                 text=True,
                 bufsize=1,
             )
@@ -145,6 +148,7 @@ class BridgeGUI(tk.Tk):
         threading.Thread(target=self._reader_thread, daemon=True).start()
         self.status_var.set("Running...")
         self._append_log("== Bridge started ==\n")
+        self.mark_btn.configure(state="normal")
 
     def stop_bridge(self) -> None:
         if self.process and self.process.poll() is None:
@@ -155,6 +159,7 @@ class BridgeGUI(tk.Tk):
                 self.process.kill()
         self.status_var.set("Stopped")
         self._append_log("== Bridge stopped ==\n")
+        self.mark_btn.configure(state="disabled")
 
     def _reader_thread(self) -> None:
         if not self.process or not self.process.stdout:
@@ -163,12 +168,28 @@ class BridgeGUI(tk.Tk):
             self.stdout_q.put(line)
         self.stdout_q.put("<<process-exit>>")
 
+    def add_mark(self) -> None:
+        if not self.process or not self.process.stdin or self.process.poll() is not None:
+            return
+        label = simpledialog.askstring("Mark", "Enter label for mark:", parent=self)
+        if label is None or label.strip() == "":
+            return
+        try:
+            # Mimic CLI behavior: send 'm' + Enter, then label + Enter
+            self.process.stdin.write("m\n")
+            self.process.stdin.write(label.strip() + "\n")
+            self.process.stdin.flush()
+            self._append_log(f"[GUI] Mark sent: {label.strip()}\n")
+        except Exception as e:
+            messagebox.showerror("Error", f"Failed to send mark: {e}")
+
     def _poll_stdout(self) -> None:
         try:
             while True:
                 line = self.stdout_q.get_nowait()
                 if line == "<<process-exit>>":
                     self.status_var.set("Stopped")
+                    self.mark_btn.configure(state="disabled")
                     break
                 self._append_log(line)
         except queue.Empty: