--- a/testing/mozharness/mozharness/base/script.py
+++ b/testing/mozharness/mozharness/base/script.py
@@ -1662,16 +1662,20 @@ class ScriptMixin(PlatformMixin):
                         bundle.extract(entry, path=extract_to)
             except tarfile.TarError as e:
                 self.log('%s (%s)' % (e.message, filename),
                          level=error_level, exit_code=fatal_exit_code)
         else:
             self.log('No extraction method found for: %s' % filename,
                      level=error_level, exit_code=fatal_exit_code)
 
+    def is_taskcluster(self):
+        """Returns boolean indicating if we're running in TaskCluster."""
+        return 'TASKCLUSTER_INSTANCE_TYPE' in os.environ
+
 
 def PreScriptRun(func):
     """Decorator for methods that will be called before script execution.
 
     Each method on a BaseScript having this decorator will be called at the
     beginning of BaseScript.run().
 
     The return value is ignored. Exceptions will abort execution.