diff --git a/bin/leanutil.py b/bin/leanutil.py
new file mode 100644
index 000000000..6f06c9c73
--- /dev/null
+++ b/bin/leanutil.py
@@ -0,0 +1,125 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+# Released under Apache 2.0 license as described in the file LICENSE.
+#
+# Authors: Soonho Kong, Leonardo de Moura
+import os
+import subprocess
+import platform
+
+g_lean_exec_name  = "lean"
+if platform.system() == "Windows" or platform.system().startswith("MSYS"):
+    g_lean_exec_name  = "lean.exe"
+
+if platform.system().startswith("MSYS"):
+    # In MSYS platform, realpath has a strange behavior.
+    #    os.path.realpath("c:\a\b\c") => \:\a\b\c
+    g_leanutil_path   = os.path.abspath(os.path.normpath(__file__))
+else:
+    g_leanutil_path   = os.path.abspath(os.path.realpath(__file__))
+
+g_lean_bin_dir = os.path.dirname(g_leanutil_path)
+
+g_lean_path = os.path.join(g_lean_bin_dir, g_lean_exec_name)
+
+if not os.path.isfile(g_lean_path):
+    error("cannot find lean executable at " + os.path.abspath(g_lean_path))
+
+class lean_exception(Exception):
+    def __init__(self, value):
+        self.value = value
+    def __str__(self):
+        return repr(self.value)
+
+def normalize_drive_name(name):
+    if platform.system() == "Windows":
+        drive, path = os.path.splitdrive(name)
+        if drive == None:
+            return name
+        else:
+            # Leo: return drive.lower() + path
+            return path
+    else:
+        return name
+
+def is_olean(fname):
+    return fname.endswith(".olean")
+
+def is_lean(fname):
+    return fname.endswith(".lean")
+
+def is_hlean(fname):
+    return fname.endswith(".hlean")
+
+LEAN_KIND=0
+HLEAN_KIND=1
+OLEAN_KIND=2
+
+def get_lean_file_kind(fname):
+    if is_lean(fname):
+        return LEAN_KIND
+    elif is_hlean(fname):
+        return HLEAN_KIND
+    elif is_olean(fname):
+        return OLEAN_KIND
+    else:
+        raise lean_exception("unknown file kind: " + fname)
+
+def olean_to_lean(fname, kind):
+    if kind == LEAN_KIND:
+        return fname[:-5] + "lean"
+    elif kind == HLEAN_KIND:
+        return fname[:-5] + "hlean"
+    else:
+        raise lean_exception("unsupported file kind: " + kind)
+
+def lean_to_olean(fname):
+    if is_lean(fname):
+        return fname[:-4] + "olean"
+    elif is_hlean(fname):
+        return fname[:-5] + "olean"
+    else:
+        raise lean_exception("file '%s' is not a lean source file" % fname)
+
+def get_timestamp(fname):
+    try:
+        return os.path.getmtime(fname)
+    except OSError:
+        return 0
+
+def is_uptodate(fname):
+    return get_timestamp(lean_to_olean(fname)) > get_timestamp(fname)
+
+def lean_direct_deps(lean_file):
+    deps = []
+    proc = subprocess.Popen([g_lean_path, "--deps", lean_file],
+                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    output = proc.communicate()[0].decode('utf-8').replace('\r\n', '\n')
+    if not proc.returncode == 0:
+        raise lean_exception(str(output))
+    for olean_file in output.strip().splitlines():
+        if olean_file:
+            deps.append(normalize_drive_name(os.path.abspath(olean_file)))
+    return deps
+
+def lean_deps_core(lean_file, visited, deps, kind):
+    if not lean_file in visited:
+        visited[lean_file] = True
+        deps.append(lean_file)
+        for d in lean_direct_deps(lean_file):
+            d = str(d)
+            if is_olean(d):
+                d = olean_to_lean(d, kind)
+                lean_deps_core(d, visited, deps, kind)
+
+def lean_deps(lean_file):
+    visited = dict()
+    deps    = []
+    lean_deps_core(lean_file, visited, deps, get_lean_file_kind(lean_file))
+    return deps
+
+if __name__ == "__main__":
+    for fname in lean_deps("/Users/leodemoura/projects/lean/library/data/nat/default.lean"):
+        print("%s is ok: %s" % (fname, is_uptodate(fname)))