diff --git a/LICENSE.txt b/LICENSE.txt
index fc6d123..ecc5369 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -1,4 +1,5 @@
 Copyright (c) 2015 Min RK, Florian Rathgeber, Michael McNeil Forbes
+2019 Casper da Costa-Luis
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
diff --git a/README.rst b/README.rst
index 331aed7..d72805d 100644
--- a/README.rst
+++ b/README.rst
@@ -154,6 +154,20 @@ This is the same metadata used by the `init_cell nbextension`__.
 
 __ https://github.com/ipython-contrib/jupyter_contrib_nbextensions/tree/master/src/jupyter_contrib_nbextensions/nbextensions/init_cell
 
+Stripping metadata
+++++++++++++++++++
+
+This is configurable via `git config (--global) filter.nbstripout.extrakeys`.
+An example would be:
+
+    git config --global filter.nbstripout.extrakeys '
+      metadata.celltoolbar metadata.kernel_spec.display_name
+      metadata.kernel_spec.name metadata.language_info.codemirror_mode.version
+      metadata.language_info.pygments_lexer metadata.language_info.version
+      metadata.toc metadata.notify_time metadata.varInspector
+      cell.metadata.heading_collapsed cell.metadata.hidden
+      cell.metadata.code_folding cell.metadata.tags cell.metadata.init_cell'
+
 Manual filter installation
 ==========================
 
diff --git a/nbstripout/__init__.py b/nbstripout/__init__.py
new file mode 100644
index 0000000..4c1bbab
--- /dev/null
+++ b/nbstripout/__init__.py
@@ -0,0 +1,4 @@
+from ._nbstripout import install, uninstall, status, main
+from ._utils import pop_recursive, strip_output
+__all__ = ["install", "uninstall", "status", "main",
+           "pop_recursive", "strip_output"]
diff --git a/nbstripout.py b/nbstripout/_nbstripout.py
similarity index 79%
rename from nbstripout.py
rename to nbstripout/_nbstripout.py
index 645bf15..0300d91 100755
--- a/nbstripout.py
+++ b/nbstripout/_nbstripout.py
@@ -85,29 +85,11 @@
 
     *.ipynb diff=ipynb
 """
-
 from __future__ import print_function
 from argparse import ArgumentParser, RawDescriptionHelpFormatter
 import io
 import sys
-
-input_stream = None
-if sys.version_info < (3, 0):
-    import codecs
-    # Use UTF8 reader/writer for stdin/stdout
-    # http://stackoverflow.com/a/1169209
-    if sys.stdin:
-        input_stream = codecs.getreader('utf8')(sys.stdin)
-    output_stream = codecs.getwriter('utf8')(sys.stdout)
-else:
-    # Wrap input/output stream in UTF-8 encoded text wrapper
-    # https://stackoverflow.com/a/16549381
-    if sys.stdin:
-        input_stream = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
-    output_stream = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-8')
-
-__version__ = '0.3.3'
-
+from nbstripout._utils import strip_output
 try:
     # Jupyter >= 4
     from nbformat import read, write, NO_CONVERT
@@ -131,67 +113,8 @@ def read(f, as_version):
         def write(nb, f):
             return current.write(nb, f, 'json')
 
-
-def _cells(nb):
-    """Yield all cells in an nbformat-insensitive manner"""
-    if nb.nbformat < 4:
-        for ws in nb.worksheets:
-            for cell in ws.cells:
-                yield cell
-    else:
-        for cell in nb.cells:
-            yield cell
-
-
-def strip_output(nb, keep_output, keep_count):
-    """
-    Strip the outputs, execution count/prompt number and miscellaneous
-    metadata from a notebook object, unless specified to keep either the outputs
-    or counts.
-    """
-
-    nb.metadata.pop('signature', None)
-    nb.metadata.pop('widgets', None)
-
-    for cell in _cells(nb):
-
-        keep_output_this_cell = keep_output
-
-        # Keep the output for these cells, but strip count and metadata
-        if cell.metadata.get('init_cell') or cell.metadata.get('keep_output'):
-            keep_output_this_cell = True
-
-        # Remove the outputs, unless directed otherwise
-        if 'outputs' in cell:
-
-            # Default behavior strips outputs. With all outputs stripped,
-            # there are no counts to keep and keep_count is ignored.
-            if not keep_output_this_cell:
-                cell['outputs'] = []
-
-            # If keep_output_this_cell, but not keep_count, strip the counts
-            # from the output.
-            if keep_output_this_cell and not keep_count:
-                for output in cell['outputs']:
-                    if 'execution_count' in output:
-                        output['execution_count'] = None
-
-            # If keep_output_this_cell and keep_count, do nothing.
-
-        # Remove the prompt_number/execution_count, unless directed otherwise
-        if 'prompt_number' in cell and not keep_count:
-            cell['prompt_number'] = None
-        if 'execution_count' in cell and not keep_count:
-            cell['execution_count'] = None
-
-        # Always remove this metadata
-        for output_style in ['collapsed', 'scrolled']:
-            if output_style in cell.metadata:
-                cell.metadata[output_style] = False
-        if 'metadata' in cell:
-            for field in ['collapsed', 'scrolled', 'ExecuteTime']:
-                cell.metadata.pop(field, None)
-    return nb
+__all__ = ["install", "uninstall", "status", "main"]
+__version__ = '0.3.3'
 
 
 def install(attrfile=None):
@@ -273,6 +196,10 @@ def status(verbose=False):
         diff = check_output(['git', 'config', 'diff.ipynb.textconv']).strip()
         attributes = check_output(['git', 'check-attr', 'filter', '--', '*.ipynb']).strip()
         diff_attributes = check_output(['git', 'check-attr', 'diff', '--', '*.ipynb']).strip()
+        try:
+            extra_keys = check_output(['git', 'config', 'filter.nbstripout.extrakeys']).strip()
+        except CalledProcessError:
+            extra_keys = ''
         if attributes.endswith(b'unspecified'):
             if verbose:
                 print('nbstripout is not installed in repository', git_dir)
@@ -284,6 +211,7 @@ def status(verbose=False):
             print('  smudge =', smudge)
             print('  required =', required)
             print('  diff=', diff)
+            print('  extrakeys=', extra_keys)
             print('\nAttributes:\n ', attributes)
             print('\nDiff Attributes:\n ', diff_attributes)
         return 0
@@ -294,6 +222,7 @@ def status(verbose=False):
 
 
 def main():
+    from subprocess import check_output, CalledProcessError
     parser = ArgumentParser(epilog=__doc__, formatter_class=RawDescriptionHelpFormatter)
     task = parser.add_mutually_exclusive_group()
     task.add_argument('--install', action='store_true',
@@ -336,13 +265,33 @@ def main():
         print(__version__)
         sys.exit(0)
 
+    try:
+        extra_keys = check_output(['git', 'config', 'filter.nbstripout.extrakeys']).strip()
+    except CalledProcessError:
+        extra_keys = ''
+
+    input_stream = None
+    if sys.version_info < (3, 0):
+        import codecs
+        # Use UTF8 reader/writer for stdin/stdout
+        # http://stackoverflow.com/a/1169209
+        if sys.stdin:
+            input_stream = codecs.getreader('utf8')(sys.stdin)
+        output_stream = codecs.getwriter('utf8')(sys.stdout)
+    else:
+        # Wrap input/output stream in UTF-8 encoded text wrapper
+        # https://stackoverflow.com/a/16549381
+        if sys.stdin:
+            input_stream = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
+        output_stream = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-8')
+
     for filename in args.files:
         if not (args.force or filename.endswith('.ipynb')):
             continue
         try:
             with io.open(filename, 'r', encoding='utf8') as f:
                 nb = read(f, as_version=NO_CONVERT)
-            nb = strip_output(nb, args.keep_output, args.keep_count)
+            nb = strip_output(nb, args.keep_output, args.keep_count, extra_keys)
             if args.textconv:
                 write(nb, output_stream)
                 output_stream.flush()
@@ -360,7 +309,7 @@ def main():
     if not args.files and input_stream:
         try:
             nb = strip_output(read(input_stream, as_version=NO_CONVERT),
-                              args.keep_output, args.keep_count)
+                              args.keep_output, args.keep_count, extra_keys)
             write(nb, output_stream)
             output_stream.flush()
         except NotJSONError:
diff --git a/nbstripout/_utils.py b/nbstripout/_utils.py
new file mode 100644
index 0000000..4343256
--- /dev/null
+++ b/nbstripout/_utils.py
@@ -0,0 +1,104 @@
+import sys
+
+__all__ = ["pop_recursive", "strip_output"]
+
+
+def pop_recursive(d, key, default=None):
+    """dict.pop(key) where `key` is a `.`-delimited list of nested keys.
+
+    >>> d = {'a': {'b': 1, 'c': 2}}
+    >>> pop_recursive(d, 'a.c')
+    2
+    >>> d
+    {'a': {'b': 1}}
+    """
+    nested = key.split('.')
+    current = d
+    for k in nested[:-1]:
+        if hasattr(current, 'get'):
+            current = current.get(k, {})
+        else:
+            return default
+    if not hasattr(current, 'pop'):
+        return default
+    return current.pop(nested[-1], default)
+
+
+def _cells(nb):
+    """Yield all cells in an nbformat-insensitive manner"""
+    if nb.nbformat < 4:
+        for ws in nb.worksheets:
+            for cell in ws.cells:
+                yield cell
+    else:
+        for cell in nb.cells:
+            yield cell
+
+
+def strip_output(nb, keep_output, keep_count, extra_keys=''):
+    """
+    Strip the outputs, execution count/prompt number and miscellaneous
+    metadata from a notebook object, unless specified to keep either the outputs
+    or counts.
+
+    `extra_keys` could be 'metadata.foo cell.metadata.bar metadata.baz'
+    """
+    if hasattr(extra_keys, 'decode'):
+        extra_keys = extra_keys.decode()
+    extra_keys = extra_keys.split()
+    keys = {'metadata': [], 'cell': {'metadata': []}}
+    for key in extra_keys:
+        if key.startswith('metadata.'):
+            keys['metadata'].append(key[len('metadata.'):])
+        elif key.startswith('cell.metadata.'):
+            keys['cell']['metadata'].append(key[len('cell.metadata.'):])
+        else:
+            sys.stderr.write('ignoring extra key `%s`' % key)
+
+    nb.metadata.pop('signature', None)
+    nb.metadata.pop('widgets', None)
+    for field in keys['metadata']:
+        pop_recursive(nb.metadata, field)
+
+    for cell in _cells(nb):
+        keep_output_this_cell = keep_output
+
+        # Keep the output for these cells, but strip count and metadata
+        if cell.metadata.get('init_cell') or cell.metadata.get('keep_output'):
+            keep_output_this_cell = True
+
+        # Remove the outputs, unless directed otherwise
+        if 'outputs' in cell:
+
+            # Default behavior strips outputs. With all outputs stripped,
+            # there are no counts to keep and keep_count is ignored.
+            if not keep_output_this_cell:
+                cell['outputs'] = []
+
+            # If keep_output_this_cell, but not keep_count, strip the counts
+            # from the output.
+            if keep_output_this_cell and not keep_count:
+                for output in cell['outputs']:
+                    if 'execution_count' in output:
+                        output['execution_count'] = None
+
+            # If keep_output_this_cell and keep_count, do nothing.
+
+        # Remove the prompt_number/execution_count, unless directed otherwise
+        if 'prompt_number' in cell and not keep_count:
+            cell['prompt_number'] = None
+        if 'execution_count' in cell and not keep_count:
+            cell['execution_count'] = None
+
+        # Always remove this metadata
+        for output_style in ['collapsed', 'scrolled']:
+            if output_style in cell.metadata:
+                cell.metadata[output_style] = False
+        if 'metadata' in cell:
+            for field in ['collapsed', 'scrolled', 'ExecuteTime']:
+                cell.metadata.pop(field, None)
+        for (extra, fields) in keys['cell'].items():
+            if extra in cell:
+                for field in fields:
+                    pop_recursive(getattr(cell, extra), field)
+    return nb
diff --git a/setup.py b/setup.py
index c30568b..6b6f208 100644
--- a/setup.py
+++ b/setup.py
@@ -1,4 +1,4 @@
-from setuptools import setup
+from setuptools import setup, find_packages
 
 with open('README.rst') as f:
     long_description = f.read()
@@ -32,10 +32,11 @@
 
       description='Strips outputs from Jupyter and IPython notebooks',
       long_description=long_description,
-      py_modules=['nbstripout'],
+      packages=find_packages(),
+      provides=['nbstripout'],
       entry_points={
           'console_scripts': [
-              'nbstripout = nbstripout:main'
+              'nbstripout = nbstripout._nbstripout:main'
           ],
       },
 
diff --git a/tests/test-git.t b/tests/test-git.t
index 5d6674a..57843de 100644
--- a/tests/test-git.t
+++ b/tests/test-git.t
@@ -1,17 +1,43 @@
   $ git init foobar
   Initialized empty Git repository in .* (re)
   $ cd foobar
+  $ git config --local filter.nbstripout.extrakeys ' '
   $ echo -n "*.txt text" >> .git/info/attributes
   $ ${NBSTRIPOUT_EXE:-nbstripout} --is-installed
   [1]
   $ ${NBSTRIPOUT_EXE:-nbstripout} --install
   $ ${NBSTRIPOUT_EXE:-nbstripout} --is-installed
   $ git diff --no-index --no-ext-diff --unified=0 --exit-code -a --no-prefix ${TESTDIR}/test_diff.ipynb ${TESTDIR}/test_diff_output.ipynb
-  $ git diff --no-index ${TESTDIR}/test_diff.ipynb ${TESTDIR}/test_diff_different.ipynb
+  $ git diff --no-index ${TESTDIR}/test_diff.ipynb ${TESTDIR}/test_diff_different_extrakeys.ipynb
   (diff --git.*) (re)
   (index .*) (re)
   (--- .*test_diff.ipynb) (re)
-  (\+\+\+ .*test_diff_different.ipynb) (re)
+  (\+\+\+ .*test_diff_different_extrakeys.ipynb) (re)
+  @@ -6,15 +6,14 @@
+      "metadata": {},
+      "outputs": [],
+      "source": [
+  -    "print(\"aou\")"
+  +    "print(\"aou now it is different\")"
+      ]
+     }
+    ],
+    "metadata": {
+     "kernelspec": {
+      "display_name": "Python 2",
+  -   "language": "python",
+  -   "name": "python2"
+  +   "language": "python"
+     },
+     "language_info": {
+      "codemirror_mode": {
+  [1]
+  $ git config --local filter.nbstripout.extrakeys 'cell.metadata.collapsed metadata.kernelspec.name'
+  $ git diff --no-index ${TESTDIR}/test_diff.ipynb ${TESTDIR}/test_diff_different_extrakeys.ipynb
+  (diff --git.*) (re)
+  (index .*) (re)
+  (--- .*test_diff.ipynb) (re)
+  (\+\+\+ .*test_diff_different_extrakeys.ipynb) (re)
   @@ -6,7 +6,7 @@
       "metadata": {},
       "outputs": [],
diff --git a/tests/test_diff_different_extrakeys.ipynb b/tests/test_diff_different_extrakeys.ipynb
new file mode 100644
index 0000000..2dba5e9
--- /dev/null
+++ b/tests/test_diff_different_extrakeys.ipynb
@@ -0,0 +1,33 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(\"aou now it is different\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.11"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..a2daf75
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,7 @@
+from nbstripout._utils import pop_recursive
+
+
+def test_pop_recursive():
+    d = {'a': {'b': 1, 'c': 2}}
+    assert pop_recursive(d, 'a.c') == 2
+    assert d == {'a': {'b': 1}}