diff --git a/pkgs/watcher/lib/src/directory_watcher/mac_os.dart b/pkgs/watcher/lib/src/directory_watcher/mac_os.dart
index 5b1feb3..cd3a483 100644
--- a/pkgs/watcher/lib/src/directory_watcher/mac_os.dart
+++ b/pkgs/watcher/lib/src/directory_watcher/mac_os.dart
@@ -7,6 +7,8 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:path/path.dart' as p;
+
 import '../constructable_file_system_event.dart';
 import '../path_set.dart';
 import '../utils.dart';
@@ -78,7 +80,12 @@
       if (entity is! Directory) _files.add(entity.path);
     },
         onError: _emitError,
-        onDone: _readyCompleter.complete,
+        onDone: () {
+      if (_runningOnBuildbot) {
+        print("watcher is ready");
+      }
+      _readyCompleter.complete();
+    },
         cancelOnError: true);
   }
 
@@ -94,12 +101,38 @@
 
   /// The callback that's run when [Directory.watch] emits a batch of events.
   void _onBatch(List<FileSystemEvent> batch) {
+    if (_runningOnBuildbot) {
+      print("======== batch:");
+      for (var event in batch) {
+        print("  ${_formatEvent(event)}");
+      }
+
+      print("known files:");
+      for (var foo in _files.toSet()) {
+        print("  ${p.relative(foo, from: directory)}");
+      }
+    }
+
     batches++;
 
     _sortEvents(batch).forEach((path, events) {
+      var relativePath = p.relative(path, from: directory);
+      if (_runningOnBuildbot) {
+        print("events for $relativePath:\n");
+        for (var event in events) {
+          print("  ${_formatEvent(event)}");
+        }
+      }
+
       var canonicalEvent = _canonicalEvent(events);
       events = canonicalEvent == null ?
           _eventsBasedOnFileSystem(path) : [canonicalEvent];
+      if (_runningOnBuildbot) {
+        print("canonical event for $relativePath: "
+            "${_formatEvent(canonicalEvent)}");
+        print("actionable events for $relativePath: "
+            "${events.map(_formatEvent)}");
+      }
 
       for (var event in events) {
         if (event is FileSystemCreateEvent) {
@@ -113,7 +146,12 @@
             if (entity is Directory) return;
             _emitEvent(ChangeType.ADD, entity.path);
             _files.add(entity.path);
-          }, onError: _emitError, cancelOnError: true);
+          }, onError: (e, stackTrace) {
+            if (_runningOnBuildbot) {
+              print("got error listing $relativePath: $e");
+            }
+            _emitError(e, stackTrace);
+          }, cancelOnError: true);
         } else if (event is FileSystemModifyEvent) {
           assert(!event.isDirectory);
           _emitEvent(ChangeType.MODIFY, path);
@@ -125,6 +163,10 @@
         }
       }
     });
+
+    if (_runningOnBuildbot) {
+      print("========");
+    }
   }
 
   /// Sort all the events in a batch into sets based on their path.
@@ -261,6 +303,13 @@
     var fileExists = new File(path).existsSync();
     var dirExists = new Directory(path).existsSync();
 
+    if (_runningOnBuildbot) {
+      print("file existed: $fileExisted");
+      print("dir existed: $dirExisted");
+      print("file exists: $fileExists");
+      print("dir exists: $dirExists");
+    }
+
     var events = [];
     if (fileExisted) {
       if (fileExists) {
@@ -330,6 +379,10 @@
     // watch beginning.
     if (type == ChangeType.ADD && _files.contains(path)) return;
 
+    if (_runningOnBuildbot) {
+      print("emitting $type ${p.relative(path, from: directory)}");
+    }
+
     _eventsController.add(new WatchEvent(type, path));
   }
 
@@ -350,4 +403,27 @@
     }, cancelOnError: cancelOnError);
     _subscriptions.add(subscription);
   }
+
+  /// Return a human-friendly string representation of [event].
+  String _formatEvent(FileSystemEvent event) {
+    if (event == null) return 'null';
+
+    var path = p.relative(event.path, from: directory);
+    var type = event.isDirectory ? 'directory' : 'file';
+    if (event is FileSystemCreateEvent) {
+      return "create $type $path";
+    } else if (event is FileSystemDeleteEvent) {
+      return "delete $type $path";
+    } else if (event is FileSystemModifyEvent) {
+      return "modify $type $path";
+    } else if (event is FileSystemMoveEvent) {
+      return "move $type $path to "
+          "${p.relative(event.destination, from: directory)}";
+    }
+  }
+
+  // TODO(nweiz): remove this when the buildbots calm down.
+  /// Whether this code is running on a buildbot.
+  bool get _runningOnBuildbot =>
+    Platform.environment['LOGNAME'] == 'chrome-bot';
 }