1 files changed, 38 insertions, 0 deletions
diff --git a/pre_commit_hooks/check_json.py b/pre_commit_hooks/check_json.py
new file mode 100644
index 0000000..6a679fe
--- /dev/null
+++ b/pre_commit_hooks/check_json.py
@@ -0,0 +1,38 @@
+from __future__ import annotations
+
+import argparse
+import json
+from typing import Any
+from typing import Sequence
+
+
+def raise_duplicate_keys(
+        ordered_pairs: list[tuple[str, Any]],
+) -> dict[str, Any]:
+    d = {}
+    for key, val in ordered_pairs:
+        if key in d:
+            raise ValueError(f'Duplicate key: {key}')
+        else:
+            d[key] = val
+    return d
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*', help='Filenames to check.')
+    args = parser.parse_args(argv)
+
+    retval = 0
+    for filename in args.filenames:
+        with open(filename, 'rb') as f:
+            try:
+                json.load(f, object_pairs_hook=raise_duplicate_keys)
+            except ValueError as exc:
+                print(f'{filename}: Failed to json decode ({exc})')
+                retval = 1
+    return retval
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())