diff --git a/tools/field-null-percent/check-null-fields.py b/tools/field-null-percent/check-null-fields.py
new file mode 100755
index 0000000..c11d51a
--- /dev/null
+++ b/tools/field-null-percent/check-null-fields.py
@@ -0,0 +1,149 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2018 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Retrieves the counts of how many objects have a particular field null on all running processes.
+
+Prints a json map from pid -> (log-tag, field-name, null-count, total-count).
+"""
+
+
+import adb
+import argparse
+import concurrent.futures
+import itertools
+import json
+import logging
+import os
+import os.path
+import signal
+import subprocess
+import time
+
+def main():
+  parser = argparse.ArgumentParser(description="Get counts of null fields from a device.")
+  parser.add_argument("-S", "--serial", metavar="SERIAL", type=str,
+                      required=False,
+                      default=os.environ.get("ANDROID_SERIAL", None),
+                      help="Android serial to use. Defaults to ANDROID_SERIAL")
+  parser.add_argument("-p", "--pid", required=False,
+                      default=[], action="append",
+                      help="Specific pids to check. By default checks all running dalvik processes")
+  has_out = "OUT" in os.environ
+  def_32 = os.path.join(os.environ.get("OUT", ""), "system", "lib", "libfieldnull.so")
+  def_64 = os.path.join(os.environ.get("OUT", ""), "system", "lib64", "libfieldnull.so")
+  has_32 = has_out and os.path.exists(def_32)
+  has_64 = has_out and os.path.exists(def_64)
+  def pushable_lib(name):
+    if os.path.isfile(name):
+      return name
+    else:
+      raise argparse.ArgumentTypeError(name + " is not a file!")
+  parser.add_argument('--lib32', type=pushable_lib,
+                      required=not has_32,
+                      action='store',
+                      default=def_32,
+                      help="Location of 32 bit agent to push")
+  parser.add_argument('--lib64', type=pushable_lib,
+                      required=not has_64,
+                      action='store',
+                      default=def_64 if has_64 else None,
+                      help="Location of 64 bit agent to push")
+  parser.add_argument("fields", nargs="+",
+                      help="fields to check")
+
+  out = parser.parse_args()
+
+  device = adb.device.get_device(out.serial)
+  print("getting root")
+  device.root()
+
+  print("Disabling selinux")
+  device.shell("setenforce 0".split())
+
+  print("Pushing libraries")
+  lib32 = device.shell("mktemp".split())[0].strip()
+  lib64 = device.shell("mktemp".split())[0].strip()
+
+  print(out.lib32 + " -> " + lib32)
+  device.push(out.lib32, lib32)
+
+  print(out.lib64 + " -> " + lib64)
+  device.push(out.lib64, lib64)
+
+  cmd32 = "'{}={}'".format(lib32, ','.join(out.fields))
+  cmd64 = "'{}={}'".format(lib64, ','.join(out.fields))
+
+  if len(out.pid) == 0:
+    print("Getting jdwp pids")
+    new_env = dict(os.environ)
+    new_env["ANDROID_SERIAL"] = device.serial
+    p = subprocess.Popen([device.adb_path, "jdwp"], env=new_env, stdout=subprocess.PIPE)
+    # ADB jdwp doesn't ever exit so just kill it after 1 second to get a list of pids.
+    with concurrent.futures.ProcessPoolExecutor() as ppe:
+      ppe.submit(kill_it, p.pid).result()
+    out.pid = p.communicate()[0].strip().split()
+    p.wait()
+    print(out.pid)
+  print("Clearing logcat")
+  device.shell("logcat -c".split())
+  final = {}
+  print("Getting info from every process dumped to logcat")
+  for p in out.pid:
+    res = check_single_process(p, device, cmd32, cmd64);
+    if res is not None:
+      final[p] = res
+  device.shell('rm {}'.format(lib32).split())
+  device.shell('rm {}'.format(lib64).split())
+  print(json.dumps(final, indent=2))
+
+def kill_it(p):
+  time.sleep(1)
+  os.kill(p, signal.SIGINT)
+
+def check_single_process(pid, device, bit32, bit64):
+  try:
+    # Just try attaching both 32 and 64 bit. Wrong one will fail silently.
+    device.shell(['am', 'attach-agent', str(pid), bit32])
+    device.shell(['am', 'attach-agent', str(pid), bit64])
+    time.sleep(0.5)
+    device.shell('kill -3 {}'.format(pid).split())
+    time.sleep(0.5)
+    out = []
+    all_fields = []
+    lc_cmd = "logcat -d -b main --pid={} -e '^\\t.*\\t[0-9]*\\t[0-9]*$'".format(pid).split(' ')
+    for l in device.shell(lc_cmd)[0].strip().split('\n'):
+      # first 4 are just date and other useless data.
+      data = l.strip().split()[5:]
+      if len(data) < 4:
+        continue
+      # If we run multiple times many copies of the agent will be attached. Just choose one of any
+      # copies for each field.
+      field = data[1]
+      if field not in all_fields:
+        out.append((str(data[0]), str(data[1]), int(data[2]), int(data[3])))
+        all_fields.append(field)
+    if len(out) != 0:
+      print("pid: " + pid + " -> " + str(out))
+      return out
+    else:
+      return None
+  except adb.device.ShellError as e:
+    print("failed on pid " + repr(pid) + " because " + repr(e))
+    return None
+
+if __name__ == '__main__':
+  main()