diff --git a/bin/crawl-url b/bin/crawl-url
index 17c6d72..b83d202 100755
--- a/bin/crawl-url
+++ b/bin/crawl-url
@@ -6,6 +6,7 @@ import os
 import sys
 import logging
 import umbra
+import umbra.frontier
 
 arg_parser = argparse.ArgumentParser(prog=os.path.basename(__file__),
         description='browse-url - open urls in chrome/chromium and run behaviors',
@@ -24,16 +25,20 @@ args = arg_parser.parse_args(args=sys.argv[1:])
 logging.basicConfig(stream=sys.stdout, level=args.log_level,
         format='%(asctime)s %(process)d %(levelname)s %(threadName)s %(name)s.%(funcName)s(%(filename)s:%(lineno)d) %(message)s')
 
-frontier = list(args.urls)
+frontier = umbra.frontier.Frontier()
+for url in args.urls:
+    frontier.schedule(umbra.frontier.CrawlUrl(url, priority=1000))
 
-def add_to_frontier(urls):
+def frontier_schedule(urls):
     logging.info("adding {} urls to frontier".format(len(urls)))
-    frontier.extend(urls)
+    for url in urls:
+        frontier.schedule(umbra.frontier.CrawlUrl(url))
 
 with umbra.Browser(chrome_exe=args.chrome_exe) as browser:
     try:
         while True:
-            browser.browse_page(frontier.pop(), on_outlinks=add_to_frontier)
+            crawl_url = frontier.pop()
+            browser.browse_page(crawl_url.url, on_outlinks=frontier_schedule)
     except IndexError:
         logging.info("finished, frontier is empty")
 
diff --git a/setup.py b/setup.py
index 258e962..6c78b07 100644
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@ setuptools.setup(name='umbra',
         license='Apache License 2.0',
         packages=['umbra'],
         package_data={'umbra':['behaviors.d/*.js*', 'behaviors.yaml', 'version.txt']},
-        install_requires=['kombu', 'websocket-client-py3==0.13.1', 'argparse', 'PyYAML'],
+        install_requires=['kombu', 'websocket-client-py3==0.13.1', 'argparse', 'PyYAML', 'sortedcontainers'],
         scripts=glob.glob('bin/*'),
         zip_safe=False,
         classifiers=[
diff --git a/umbra/frontier.py b/umbra/frontier.py
new file mode 100644
index 0000000..52cdfe5
--- /dev/null
+++ b/umbra/frontier.py
@@ -0,0 +1,67 @@
+#!/usr/bin/env python
+# vim: set sw=4 et:
+
+import logging
+import sys
+import urllib.parse
+import sortedcontainers
+
+class CrawlUrl:
+    def __init__(self, url, priority=1):
+        self.url = url
+        self.set_priority(priority)
+        self._netloc = None
+
+    def set_priority(self, priority):
+        # priority_key is both a sortable priority (higher value is higher
+        # priority) and a unique hash key
+        self.priority_key = (priority << 32) | (hash(self.url) & (2**32 - 1))
+
+    def get_priority(self):
+        return self.priority >> 32
+
+    @property
+    def host(self):
+        if self._netloc is None:
+            self._netloc = urllib.parse.urlsplit(self.url)[1]
+        return self._netloc
+
+class Frontier:
+    def __init__(self):
+        # {url:CrawlUrl}
+        self.urls = {} 
+        
+        # {host:SortedDict{priority_key:CrawlUrl}}
+        self.queues_by_host = {}
+
+    def schedule(self, crawl_url):
+        try:
+            old_priority_key = self.urls.pop(crawl_url.url).priority_key
+            old_crawl_url = self.queues_by_host[crawl_url.host].pop(old_priority_key)
+
+            # XXX very dumb calculation of new priority, probably doesn't belong here
+            crawl_url.set_priority(crawl_url.get_priority() + old_crawl_url.get_priority())
+        except KeyError:
+            pass
+
+        self.urls[crawl_url.url] = crawl_url
+        if crawl_url.host not in self.queues_by_host:
+            self.queues_by_host[crawl_url.host] = sortedcontainers.SortedDict()
+        self.queues_by_host[crawl_url.host][crawl_url.priority_key] = crawl_url
+
+    def pop(self, host=None):
+        if not host or host not in self.queues_by_host:
+            # XXX should prioritize queues, this picks one at random
+            for h in self.queues_by_host:
+                host = h
+                break
+
+        result = self.queues_by_host[host].popitem(last=True)[1]
+        if len(self.queues_by_host[host]) == 0:
+            del self.queues_by_host[host]
+
+        result2 = self.urls.pop(result.url)
+        assert result2 is result
+
+        return result
+