diff --git a/README.md b/README.md
index 5367352..e6044b2 100644
--- a/README.md
+++ b/README.md
@@ -57,9 +57,16 @@
 performance traces and attach a gdb debugger.
 
 #### Tracing
-To collect [performance
+In order to collect [performance
 traces](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool)
-and retrieve the result:
+interactively through `mojo_debug`, make sure that the app being inspected was
+run with `--debugger` switch. E.g.:
+
+```sh
+mojo_run --debugger APP_URL [--android]
+```
+
+Then, in another shell, tracing can be orchestrated as follows:
 
 ```sh
 mojo_debug tracing start
diff --git a/mojo_debug b/mojo_debug
index 31a93de..cc1aa0b 100755
--- a/mojo_debug
+++ b/mojo_debug
@@ -45,7 +45,10 @@
     else:
       return requests.get(url)
   except requests.exceptions.ConnectionError:
-    print 'Failed to connect to mojo:debugger, make sure the shell is running.'
+    print ('Failed to connect to debugger.mojo. Make sure the shell is running '
+           'and the app was started with debugger, ie. through '
+           '`mojo_run --debugger APP_URL`')
+
     return None
 
 
@@ -91,7 +94,7 @@
 def _add_tracing_command(subparsers):
   """Sets up the command line parser to manage tracing."""
   tracing_parser = subparsers.add_parser('tracing',
-      help='trace event profiler')
+      help='tracer (requires debugger.mojo)')
   tracing_subparser = tracing_parser.add_subparsers(
       help='the command to run')
 
@@ -115,7 +118,8 @@
 
 def _add_wm_command(subparsers):
   """Sets up the parser for the 'wm' command."""
-  wm_parser = subparsers.add_parser('wm', help='window manager')
+  wm_parser = subparsers.add_parser('wm', help='window manager (requires '
+                                    'debugger.mojo)')
   wm_subparser = wm_parser.add_subparsers(
       help='the command to run')
 
diff --git a/mojo_run b/mojo_run
index 541afb9..0982ee6 100755
--- a/mojo_run
+++ b/mojo_run
@@ -40,10 +40,11 @@
 
 _LEGACY_WM_URL = 'mojo:window_manager'
 _WM_URL = 'https://core.mojoapps.io/window_manager.mojo'
+_DEBUGGER_URL = 'https://core.mojoapps.io/debugger.mojo'
 
 
 def _configure_debugger(shell):
-  """Configures mojo:debugger to run and sets up port forwarding for its http
+  """Configures debugger.mojo to run and sets up port forwarding for its http
   server if the shell is running on a device.
 
   Returns:
@@ -51,7 +52,7 @@
     run with the debugger.
   """
   shell.forward_host_port_to_shell(_MOJO_DEBUGGER_PORT)
-  return ['mojo:debugger %d' % _MOJO_DEBUGGER_PORT]
+  return ['%s %d' % (_DEBUGGER_URL, _MOJO_DEBUGGER_PORT)]
 
 
 def main():
@@ -66,8 +67,8 @@
                       help='Window manager app to be mapped as '
                       'mojo:window_manager. By default it is ' +
                       _DEFAULT_WM)
-  parser.add_argument('--no-debugger', action="store_true",
-                      help='Do not spawn mojo:debugger.')
+  parser.add_argument('--debugger', action="store_true",
+                      help='Run debugger.mojo along with the app.')
 
   script_args, shell_args = parser.parse_known_args()
 
@@ -88,7 +89,7 @@
   if script_args.embed:
     shell_args.append('%s %s' % (script_args.window_manager, script_args.embed))
 
-  if not script_args.no_debugger:
+  if script_args.debugger:
     if script_args.verbose:
       print 'Spawning mojo:debugger, use `mojo_debug` to inspect the shell.'
       print 'Note that mojo:debugger will prevent the shell from terminating,'