diff --git a/pre_commit/clientlib.py b/pre_commit/clientlib.py
index 2f16650a..a16a73ac 100644
--- a/pre_commit/clientlib.py
+++ b/pre_commit/clientlib.py
@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 import argparse
 import functools
+import logging
 import pipes
 import sys
 
@@ -15,6 +16,8 @@ from pre_commit.error_handler import FatalError
 from pre_commit.languages.all import all_languages
 from pre_commit.util import parse_version
 
+logger = logging.getLogger('pre_commit')
+
 
 def check_type_tag(tag):
     if tag not in ALL_TAGS:
@@ -144,6 +147,16 @@ def _entry(modname):
     )
 
 
+def warn_on_unknown_keys_at_top_level(extra, orig_keys):
+    logger.warning(
+        'Your pre-commit-config contain these extra keys: {}. '
+        'while the only valid keys are: {}.'.format(
+            ', '.join(extra),
+            ', '.join(sorted(orig_keys)),
+        ),
+    ),
+
+
 _meta = (
     (
         'check-hooks-apply', (
@@ -222,6 +235,10 @@ CONFIG_REPO_DICT = cfgv.Map(
     ),
 
     MigrateShaToRev(),
+    cfgv.WarnAdditionalKeys(
+        {'repo', 'rev', 'hooks'},
+        warn_on_unknown_keys_at_top_level,
+    ),
 )
 DEFAULT_LANGUAGE_VERSION = cfgv.Map(
     'DefaultLanguageVersion', None,
diff --git a/tests/clientlib_test.py b/tests/clientlib_test.py
index 2cdc1528..069dca36 100644
--- a/tests/clientlib_test.py
+++ b/tests/clientlib_test.py
@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 
+import logging
+
 import cfgv
 import pytest
 
@@ -116,6 +118,27 @@ def test_validate_config_old_list_format_ok(tmpdir):
     assert not validate_config_main((f.strpath,))
 
 
+def test_validate_warn_on_unknown_keys_at_top_level(tmpdir, caplog):
+    f = tmpdir.join('cfg.yaml')
+    f.write(
+        '-   repo: https://gitlab.com/pycqa/flake8\n'
+        '    rev: 3.7.7\n'
+        '    hooks:\n'
+        '    -   id: flake8\n'
+        '    args: [--some-args]\n',
+    )
+    ret_val = validate_config_main((f.strpath,))
+    assert not ret_val
+    assert caplog.record_tuples == [
+        (
+            'pre_commit',
+            logging.WARNING,
+            'Your pre-commit-config contain these extra keys: args. '
+            'while the only valid keys are: hooks, repo, rev.',
+        ),
+    ]
+
+
 @pytest.mark.parametrize('fn', (validate_config_main, validate_manifest_main))
 def test_mains_not_ok(tmpdir, fn):
     not_yaml = tmpdir.join('f.notyaml')