diff --git a/src/rpmroute/cli.py b/src/rpmroute/cli.py
index 468d929..2879603 100644
--- a/src/rpmroute/cli.py
+++ b/src/rpmroute/cli.py
@@ -94,11 +94,12 @@ def build_parser() -> argparse.ArgumentParser:
     parser.add_argument(
         "--engine",
         choices=sorted(ENGINE_OPTIONS),
-        default="grid",
+        default="exact",
         help=(
-            "routing track: grid (default; multi-layer rip-up maze, highest coverage), "
-            "exact (orthogonal, exact-geometry DRC-verified output), "
-            "room (continuous expansion rooms, routes off-grid channels)"
+            "routing track: exact (default; every route checked against exact pad and "
+            "copper shapes, DRC-clean output), grid (quick maze on the grid alone: its "
+            "copper is NOT clearance-checked and can short), room (continuous expansion "
+            "rooms, routes off-grid channels; not clearance-checked either)"
         ),
     )
     parser.add_argument(
@@ -386,6 +387,17 @@ def main(argv: list[str] | None = None) -> int:
         for net, a, b, zone in in_zone:
             print(f"  {net}: {a} to {b} (both in zone {zone})", file=sys.stderr)
 
+    if args.engine != "exact":
+        # These engines route on approximations and do not check the copper
+        # they write against exact shapes: a board can come out with shorts
+        # that this report would otherwise never mention.
+        print(
+            f"rpmroute: WARNING: the {args.engine} engine does not check its copper for "
+            "clearance or shorts; run KiCad's DRC on the result, or route with "
+            "--engine exact (the default)",
+            file=sys.stderr,
+        )
+
     if args.output:
         with open(args.output, "w", encoding="utf-8") as f:
             f.write(ses_text)
diff --git a/tests/test_cli.py b/tests/test_cli.py
index cc64dc7..f0d129e 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -71,13 +71,25 @@ def test_cli_every_engine_routes_a_fixture(engine, tmp_path):
     assert "(wire" in text
 
 
-def test_cli_default_engine_is_grid(tmp_path):
-    """The default must stay grid — the drop-in JAR replacement behaviour."""
+def test_cli_default_engine_is_exact(tmp_path):
+    """The default is the engine that checks its copper: grid output can short
+    and say nothing (a user routing with no flags shipped 15 crossings)."""
     default = tmp_path / "default.ses"
-    grid = tmp_path / "grid.ses"
+    exact = tmp_path / "exact.ses"
     assert main([str(FIXTURE), "-do", str(default)]) == 0
-    assert main([str(FIXTURE), "--engine", "grid", "-do", str(grid)]) == 0
-    assert default.read_text() == grid.read_text()
+    assert main([str(FIXTURE), "--engine", "exact", "-do", str(exact)]) == 0
+    assert default.read_text() == exact.read_text()
+
+
+@pytest.mark.parametrize("engine", ["grid", "room"])
+def test_unchecked_engines_say_so(tmp_path, capsys, engine):
+    assert main([str(FIXTURE), "--engine", engine, "-do", str(tmp_path / "out.ses")]) == 0
+    assert "does not check its copper" in capsys.readouterr().err
+
+
+def test_the_exact_engine_does_not_warn(tmp_path, capsys):
+    assert main([str(FIXTURE), "-do", str(tmp_path / "out.ses")]) == 0
+    assert "WARNING" not in capsys.readouterr().err
 
 
 def test_cli_room_pack_routes(tmp_path):