diff --git a/setup.py b/setup.py
index aec3953..20e9bc5 100644
--- a/setup.py
+++ b/setup.py
@@ -9,7 +9,6 @@ def full_version_bytes():
     import subprocess, time
     try:
         commit_bytes = subprocess.check_output(['git', 'log', '-1', '--pretty=format:%h'])
-
         t_bytes = subprocess.check_output(['git', 'log', '-1', '--pretty=format:%ct'])
         t = int(t_bytes.strip().decode('utf-8'))
         tm = time.gmtime(t)
@@ -32,8 +31,8 @@ setuptools.setup(name='umbra',
         long_description=open('README.md').read(),
         license='Apache License 2.0',
         packages=['umbra'],
-        package_data={'umbra':['behaviors.d/*.js', 'version.txt']},
-        install_requires=['kombu', 'websocket-client-py3==0.13.1','argparse'],
+        package_data={'umbra':['behaviors.d/*.js', 'behaviors.yaml', 'version.txt']},
+        install_requires=['kombu', 'websocket-client-py3==0.13.1', 'argparse', 'PyYAML'],
         scripts=glob.glob('bin/*'),
         zip_safe=False,
         classifiers=[
diff --git a/umbra/behaviors.d/default.js b/umbra/behaviors.d/default.js
index dc66819..4470cab 100644
--- a/umbra/behaviors.d/default.js
+++ b/umbra/behaviors.d/default.js
@@ -1,5 +1,3 @@
-// {"request_idle_timeout_sec":10}
-//
 // vim:set sw=8 et:
 //
 // Scrolls to the bottom of the page. That's it at the moment.
diff --git a/umbra/behaviors.d/facebook.js b/umbra/behaviors.d/facebook.js
index e2eb271..a61f484 100644
--- a/umbra/behaviors.d/facebook.js
+++ b/umbra/behaviors.d/facebook.js
@@ -1,7 +1,4 @@
-// {"url_regex":"^https?://(?:www\\.)?facebook\\.com/.*$", "request_idle_timeout_sec":30}
-//
 // vim:set sw=8 et:
-//
 
 var umbraAboveBelowOrOnScreen = function(e) {
         var eTop = e.getBoundingClientRect().top;
diff --git a/umbra/behaviors.d/flickr.js b/umbra/behaviors.d/flickr.js
index 65787a9..a341480 100644
--- a/umbra/behaviors.d/flickr.js
+++ b/umbra/behaviors.d/flickr.js
@@ -1,7 +1,4 @@
-// {"url_regex":"^https?://(?:www\\.)?flickr\\.com/.*$", "request_idle_timeout_sec":10}
-//
 // vim:set sw=8 et:
-//
 
 setInterval(function() { window.scrollBy(0,50); }, 100);
 
diff --git a/umbra/behaviors.d/marquette_edu.js b/umbra/behaviors.d/marquette_edu.js
index cdaab00..76cd85c 100644
--- a/umbra/behaviors.d/marquette_edu.js
+++ b/umbra/behaviors.d/marquette_edu.js
@@ -1,7 +1,4 @@
-// {"url_regex":"^https?://(?:www\\.)?marquette\\.edu/.*$", "request_idle_timeout_sec":10}
-//
 // vim:set sw=8 et:
-//
 
 var umbraState = {'idleSince':null};
 var umbraIntervalID = setInterval(umbraScrollInterval,50);
diff --git a/umbra/behaviors.d/vimeo.js b/umbra/behaviors.d/vimeo.js
index 53860f2..72a10cb 100644
--- a/umbra/behaviors.d/vimeo.js
+++ b/umbra/behaviors.d/vimeo.js
@@ -1,7 +1,4 @@
-// {"url_regex":"^https?://(?:www\\.)?vimeo\\.com/.*$", "request_idle_timeout_sec":10}
-//
 // vim:set sw=8 et:
-//
 
 var umbraState = {'idleSince':null};
 var umbraVideoElements = document.getElementsByTagName('video');
diff --git a/umbra/behaviors.py b/umbra/behaviors.py
index 41e6055..43cd53b 100644
--- a/umbra/behaviors.py
+++ b/umbra/behaviors.py
@@ -7,45 +7,28 @@ import re
 import logging
 import time
 import sys
+import yaml
 
 class Behavior:
     logger = logging.getLogger(__module__ + "." + __qualname__)
 
     _behaviors = None
-    _default_behavior = None
 
     @staticmethod
     def behaviors():
         if Behavior._behaviors is None:
-            behaviors_directory = os.path.sep.join(__file__.split(os.path.sep)[:-1] + ['behaviors.d'])
-            behavior_files = itertools.chain(*[[os.path.join(dir, file) for file in files if file.endswith('.js') and file != 'default.js'] for dir, dirs, files in os.walk(behaviors_directory)])
-            Behavior._behaviors = []
-            for file_name in behavior_files:
-                Behavior.logger.debug("reading behavior file {}".format(file_name))
-                script = open(file_name, encoding='utf-8').read()
-                first_line = script[:script.find('\n')]
-                behavior = json.loads(first_line[2:].strip())
-                behavior['script'] = script
-                behavior['file'] = file_name
-                Behavior._behaviors.append(behavior)
-                Behavior.logger.info("will run behaviors from {} on urls matching {}".format(file_name, behavior['url_regex']))
+            behaviors_yaml = os.path.sep.join(__file__.split(os.path.sep)[:-1] + ['behaviors.yaml'])
+            with open(behaviors_yaml) as fin:
+                conf = yaml.load(fin)
+            Behavior._behaviors = conf['behaviors']
+
+            for behavior in Behavior._behaviors:
+                if "behavior_js" in behavior:
+                    behavior_js = os.path.sep.join(__file__.split(os.path.sep)[:-1] + ["behaviors.d"] + [behavior["behavior_js"]])
+                    behavior["script"] = open(behavior_js, encoding="utf-8").read()
 
         return Behavior._behaviors
 
-    @staticmethod
-    def default_behavior():
-        if Behavior._default_behavior is None:
-            behaviors_directory = os.path.sep.join(__file__.split(os.path.sep)[:-1] + ['behaviors.d'])
-            file_name = os.path.join(behaviors_directory, 'default.js')
-            Behavior.logger.debug("reading default behavior file {}".format(file_name))
-            script = open(file_name, encoding='utf-8').read()
-            first_line = script[:script.find('\n')]
-            behavior = json.loads(first_line[2:].strip())
-            behavior['script'] = script
-            behavior['file'] = file_name
-            Behavior._default_behavior = behavior
-        return Behavior._default_behavior
-
     def __init__(self, url, umbra_worker):
         self.url = url
         self.umbra_worker = umbra_worker
@@ -58,14 +41,14 @@ class Behavior:
     def start(self):
         for behavior in Behavior.behaviors():
             if re.match(behavior['url_regex'], self.url):
+                if "behavior_js" in behavior:
+                    self.logger.info("using {} behavior for {}".format(behavior["behavior_js"], self.url))
                 self.active_behavior = behavior
-                break
-
-        if self.active_behavior is None:
-            self.active_behavior = Behavior.default_behavior()
-
-        self.umbra_worker.send_to_chrome(method="Runtime.evaluate", params={"expression": self.active_behavior['script']})
-        self.notify_of_activity()
+                self.umbra_worker.send_to_chrome(method="Runtime.evaluate",
+                        suppress_logging=True, params={"expression": behavior["script"]})
+                self.notify_of_activity()
+                return
+        self.logger.warn("no behavior to run on {}".format(self.url))
 
     def is_finished(self):
         msg_id = self.umbra_worker.send_to_chrome(method="Runtime.evaluate",
diff --git a/umbra/behaviors.yaml b/umbra/behaviors.yaml
new file mode 100644
index 0000000..84c98d3
--- /dev/null
+++ b/umbra/behaviors.yaml
@@ -0,0 +1,22 @@
+# first matched behavior is used, so order matters here
+behaviors:
+ -
+   url_regex: '^https?://(?:www\.)?facebook\.com/.*$'
+   behavior_js: facebook.js
+   request_idle_timeout_sec: 30
+ -
+   url_regex: '^https?://(?:www\.)?flickr\.com/.*$'
+   behavior_js: flickr.js
+   request_idle_timeout_sec: 10
+ -
+   url_regex: '^https?://(?:www\.)?marquette\.edu/.*$'
+   behavior_js: marquette_edu.js
+   request_idle_timeout_sec: 10
+ -
+   url_regex: '^https?://(?:www\.)?vimeo\.com/.*$'
+   behavior_js: vimeo.js
+   request_idle_timeout_sec: 10
+ -
+   url_regex: '^.*$'
+   request_idle_timeout_sec: 10
+   behavior_js: default.js