diff --git a/tools/check_logs.py b/tools/check_logs.py
index 0cc3677..2ad4f70 100755
--- a/tools/check_logs.py
+++ b/tools/check_logs.py
@@ -16,7 +16,140 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import argparse
+import gzip
+import os
+import re
+import StringIO
 import sys
+import urllib2
+import yaml
+
+
+def process_files(file_specs, url_specs, whitelists):
+    regexp = re.compile(r"^.*(ERROR|CRITICAL).*\[.*\-.*\]")
+    had_errors = False
+    for (name, filename) in file_specs:
+        whitelist = whitelists.get(name, [])
+        with open(filename) as content:
+            if scan_content(name, content, regexp, whitelist):
+                had_errors = True
+    for (name, url) in url_specs:
+        whitelist = whitelists.get(name, [])
+        req = urllib2.Request(url)
+        req.add_header('Accept-Encoding', 'gzip')
+        page = urllib2.urlopen(req)
+        buf = StringIO.StringIO(page.read())
+        f = gzip.GzipFile(fileobj=buf)
+        if scan_content(name, f.read().splitlines(), regexp, whitelist):
+            had_errors = True
+    return had_errors
+
+
+def scan_content(name, content, regexp, whitelist):
+    had_errors = False
+    for line in content:
+        if not line.startswith("Stderr:") and regexp.match(line):
+            whitelisted = False
+            for w in whitelist:
+                pat = ".*%s.*%s.*" % (w['module'].replace('.', '\\.'),
+                                      w['message'])
+                if re.match(pat, line):
+                    whitelisted = True
+                    break
+            if not whitelisted:
+                if not had_errors:
+                    print("Log File: %s" % name)
+                had_errors = True
+                print(line)
+    return had_errors
+
+
+def collect_url_logs(url):
+    page = urllib2.urlopen(url)
+    content = page.read()
+    logs = re.findall('(screen-[\w-]+\.txt\.gz)</a>', content)
+    return logs
+
+
+def main(opts):
+    if opts.directory and opts.url or not (opts.directory or opts.url):
+        print("Must provide exactly one of -d or -u")
+        exit(1)
+    print("Checking logs...")
+    WHITELIST_FILE = os.path.join(
+        os.path.abspath(os.path.dirname(os.path.dirname(__file__))),
+        "etc", "whitelist.yaml")
+
+    file_matcher = re.compile(r".*screen-([\w-]+)\.log")
+    files = []
+    if opts.directory:
+        d = opts.directory
+        for f in os.listdir(d):
+            files.append(os.path.join(d, f))
+    files_to_process = []
+    for f in files:
+        m = file_matcher.match(f)
+        if m:
+            files_to_process.append((m.group(1), f))
+
+    url_matcher = re.compile(r".*screen-([\w-]+)\.txt\.gz")
+    urls = []
+    if opts.url:
+        for logfile in collect_url_logs(opts.url):
+            urls.append("%s/%s" % (opts.url, logfile))
+    urls_to_process = []
+    for u in urls:
+        m = url_matcher.match(u)
+        if m:
+            urls_to_process.append((m.group(1), u))
+
+    whitelists = {}
+    with open(WHITELIST_FILE) as stream:
+        loaded = yaml.safe_load(stream)
+        if loaded:
+            for (name, l) in loaded.iteritems():
+                for w in l:
+                    assert 'module' in w, 'no module in %s' % name
+                    assert 'message' in w, 'no message in %s' % name
+            whitelists = loaded
+    if process_files(files_to_process, urls_to_process, whitelists):
+        print("Logs have errors")
+        # Return non-zero to start failing builds
+        return 0
+    else:
+        print("ok")
+        return 0
+
+usage = """
+Find non-white-listed log errors in log files from a devstack-gate run.
+Log files will be searched for ERROR or CRITICAL messages. If any
+error messages do not match any of the whitelist entries contained in
+etc/whitelist.yaml, those messages will be printed to the console and
+failure will be returned. A file directory containing logs or a url to the
+log files of an OpenStack gate job can be provided.
+
+The whitelist yaml looks like:
+
+log-name:
+    - module: "a.b.c"
+      message: "regexp"
+    - module: "a.b.c"
+      message: "regexp"
+
+repeated for each log file with a whitelist.
+"""
+
+parser = argparse.ArgumentParser(description=usage)
+parser.add_argument('-d', '--directory',
+                    help="Directory containing log files")
+parser.add_argument('-u', '--url',
+                    help="url containing logs from an OpenStack gate job")
 
 if __name__ == "__main__":
-    sys.exit(0)
+    try:
+        sys.exit(main(parser.parse_args()))
+    except Exception as e:
+        print("Failure in script: %s" % e)
+        # Don't fail if there is a problem with the script.
+        sys.exit(0)