diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 690a5de..eb37be1 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -15,6 +15,14 @@ pytest
 ruff check .
 ```
 
+Auto-format and auto-fix what ruff can fix on its own:
+
+```bash
+scripts/format.sh
+```
+
+Use `scripts/format.sh --check` to verify formatting without writing changes.
+
 ## Documentation
 
 User-facing documentation lives in [docs/](docs/) and is built with MkDocs. If you change or add public behaviour, update the relevant page there.
diff --git a/scripts/format.sh b/scripts/format.sh
new file mode 100755
index 0000000..64f7816
--- /dev/null
+++ b/scripts/format.sh
@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Auto-format the codebase and fix auto-fixable lint issues with ruff.
+#
+# Usage:
+#   scripts/format.sh          # format in place
+#   scripts/format.sh --check  # fail if anything would change, don't write (for CI)
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+if [[ "${1:-}" == "--check" ]]; then
+    ruff format --check .
+    ruff check .
+else
+    ruff format .
+    ruff check --fix .
+fi
diff --git a/src/earthrs/processing/atmospheric.py b/src/earthrs/processing/atmospheric.py
index ea42ff6..533630b 100644
--- a/src/earthrs/processing/atmospheric.py
+++ b/src/earthrs/processing/atmospheric.py
@@ -18,4 +18,4 @@ def atmospheric_correction(scene: Scene, *, method: str = "default", **kwargs: A
     _ = kwargs
     raise NotImplementedError(
         "Atmospheric correction is not yet implemented. Check for a new version of earthrs."
-    )
\ No newline at end of file
+    )