diff --git a/tests/test_review.py b/tests/test_review.py
new file mode 100644
index 0000000..5fb9d2a
--- /dev/null
+++ b/tests/test_review.py
@@ -0,0 +1,59 @@
+from hef.catalog import Record, validate
+from hef.selection import Coordinate
+from tools.review import approve, proposed_records
+
+
+def make_record(**o):
+    base = dict(
+        id="a",
+        title="t",
+        source_url="u",
+        source_archive="nasa",
+        license="public_domain",
+        mode="video",
+        left=0,
+        right=0,
+        dark=0,
+        light=0,
+        duration_s=1,
+        file_path="p",
+    )
+    base.update(o)
+    return Record(**base)
+
+
+def test_proposed_records_filters():
+    a = make_record(id="a", review_status="proposed")
+    b = make_record(id="b", review_status="approved")
+    assert [r.id for r in proposed_records([a, b])] == ["a"]
+
+
+def test_approve_sets_status_and_timestamp():
+    r = make_record(review_status="proposed")
+    out = approve(r, reviewed_at="2026-06-04T13:00:00+00:00")
+    assert out.review_status == "approved"
+    assert out.reviewed_at == "2026-06-04T13:00:00+00:00"
+
+
+def test_approve_can_override_coordinates():
+    r = make_record(left=0, right=0, dark=0, light=0, review_status="proposed")
+    out = approve(r, reviewed_at="t", coordinate=Coordinate(4, 1, 2, 3))
+    assert (out.left, out.right, out.dark, out.light) == (4, 1, 2, 3)
+
+
+def test_approve_does_not_mutate_input():
+    r = make_record(review_status="proposed")
+    approve(r, reviewed_at="t")
+    assert r.review_status == "proposed" and r.reviewed_at is None
+
+
+def test_approve_can_set_rationale():
+    r = make_record(review_status="proposed", rationale="auto")
+    out = approve(r, reviewed_at="t", rationale="human note")
+    assert out.rationale == "human note"
+
+
+def test_approved_record_revalidates():
+    r = make_record(review_status="proposed")
+    out = approve(r, reviewed_at="t", coordinate=Coordinate(2, 2, 1, 1))
+    validate(out)  # must not raise
diff --git a/tools/review.py b/tools/review.py
new file mode 100644
index 0000000..90467b9
--- /dev/null
+++ b/tools/review.py
@@ -0,0 +1,34 @@
+"""Review state-transition core (pure, tested): proposed -> approved.
+
+No I/O, no clock — the timestamp is injected so the logic stays deterministic.
+The CLI persists the result via hef.catalog.save_catalog after re-validating.
+"""
+
+from __future__ import annotations
+
+from dataclasses import replace
+
+
+def proposed_records(records):
+    """Records still awaiting review."""
+    return [r for r in records if r.review_status == "proposed"]
+
+
+def approve(record, *, reviewed_at, coordinate=None, rationale=None):
+    """Return an approved copy of `record` (the input is not mutated).
+
+    review_status -> 'approved' and reviewed_at is stamped. Optionally override
+    the four coordinates with a human correction and/or replace the rationale.
+    The caller re-validates before saving.
+    """
+    changes = {"review_status": "approved", "reviewed_at": reviewed_at}
+    if coordinate is not None:
+        changes.update(
+            left=coordinate.left,
+            right=coordinate.right,
+            dark=coordinate.dark,
+            light=coordinate.light,
+        )
+    if rationale is not None:
+        changes["rationale"] = rationale
+    return replace(record, **changes)