diff --git a/crates/engine/src/cmd/slices.rs b/crates/engine/src/cmd/slices.rs
index cc8598a5c..c2092da0a 100644
--- a/crates/engine/src/cmd/slices.rs
+++ b/crates/engine/src/cmd/slices.rs
@@ -14,7 +14,7 @@ use vectorcraft_geom::{Rect, shapes};
 
 use super::{
     CommandSpec, EngineError, NodeId, Result, Session, bad, bool_or, cmd, f64_or, f64_req, has_doc, has_selection, id_param, ids_param, index,
-    targets,
+    switch_or, targets,
 };
 
 /// The most slices one Divide Slices makes.
@@ -593,7 +593,7 @@ fn options(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 fn clip_to_artboard(s: &mut Session, p: &Value) -> Result<Value> {
-    let on = p.get("on").and_then(Value::as_bool).unwrap_or(!s.doc()?.doc.slices_clip_to_artboard);
+    let on = switch_or(p, "on", !s.doc()?.doc.slices_clip_to_artboard, "object.slice.clipToArtboard")?;
     if on != s.doc()?.doc.slices_clip_to_artboard {
         s.edit("Clip to Artboard", |d, _| {
             d.slices_clip_to_artboard = on;
@@ -604,7 +604,7 @@ fn clip_to_artboard(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 fn hide(s: &mut Session, p: &Value) -> Result<Value> {
-    let v = p.get("hidden").and_then(Value::as_bool).unwrap_or(!s.menu.slices_hidden);
+    let v = switch_or(p, "hidden", !s.menu.slices_hidden, "view.slices.hide")?;
     s.menu.slices_hidden = v;
     if v {
         deselect_in_every_document(s);
@@ -613,7 +613,7 @@ fn hide(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 fn lock(s: &mut Session, p: &Value) -> Result<Value> {
-    let v = p.get("locked").and_then(Value::as_bool).unwrap_or(!s.menu.slices_locked);
+    let v = switch_or(p, "locked", !s.menu.slices_locked, "view.slices.lock")?;
     s.menu.slices_locked = v;
     if v {
         deselect_in_every_document(s);
diff --git a/crates/engine/src/tests/slices.rs b/crates/engine/src/tests/slices.rs
index 1576f50ce..87d0088d9 100644
--- a/crates/engine/src/tests/slices.rs
+++ b/crates/engine/src/tests/slices.rs
@@ -593,3 +593,27 @@ fn slice_commands_check_their_params() {
     assert!(s.doc().unwrap().doc.node(NodeId(a)).is_some(), "deleting an object slice keeps its object");
     assert_eq!(run(&mut s, "object.slice.select", json!({}))["selected"], json!([]));
 }
+
+#[test]
+fn invalid_slice_toggle_flags_do_not_change_state_or_selection() {
+    for (command, params) in [
+        ("object.slice.clipToArtboard", json!({"on": "false"})),
+        ("view.slices.hide", json!({"hidden": 0})),
+        ("view.slices.lock", json!({"locked": 1})),
+    ] {
+        let mut s = session();
+        let id = user_slice(&mut s, [10.0, 10.0, 20.0, 20.0]);
+        run(&mut s, "select.object.slices", json!({}));
+        let before_undo = s.doc().unwrap().history.undo.len();
+        assert!(s.execute(command, &params).is_err(), "{command} accepted {params}");
+        assert!(s.doc().unwrap().doc.slices_clip_to_artboard, "{command} changed the document");
+        assert!(!s.slices_hidden(), "{command} hid slices");
+        assert!(!s.slices_locked(), "{command} locked slices");
+        assert_eq!(s.doc().unwrap().selection.slices, vec![NodeId(id)], "{command} cleared the selection");
+        assert_eq!(s.doc().unwrap().history.undo.len(), before_undo, "{command} recorded an undo step");
+    }
+    // Left out, or null as for every command, the flag toggles.
+    let mut s = session();
+    assert_eq!(run(&mut s, "view.slices.hide", Value::Null)["hidden"], true);
+    assert_eq!(run(&mut s, "view.slices.hide", json!({"hidden": null}))["hidden"], false);
+}
diff --git a/docs/mcp.md b/docs/mcp.md
index ccc9147b7..5c9c5cb45 100644
--- a/docs/mcp.md
+++ b/docs/mcp.md
@@ -4466,6 +4466,7 @@ deselects the slices in every open document; unlocking or showing them again lea
 restore the selection that was cleared. While the slices are locked or hidden, a command that selects slices, such as
 `select.object.slices` (which replies `count: 0`), `object.slice.select`, `object.slice.create`, `edit.undo` or
 `edit.redo`, leaves them out; a selected object that is an object slice stays selected.
+`object.slice.clipToArtboard`, `view.slices.hide`, and `view.slices.lock` reject a flag that is not a boolean. Omitting the flag toggles its current value.
 
 ```json
 {"name":"run_command","arguments":{"command":"object.slice.make","params":{}}}