diff --git a/crates/engine/src/fx_view_cmds.rs b/crates/engine/src/fx_view_cmds.rs
index 76bbc781ee..af550a367b 100644
--- a/crates/engine/src/fx_view_cmds.rs
+++ b/crates/engine/src/fx_view_cmds.rs
@@ -10,10 +10,12 @@ use crate::{EngineError, Result, Session};
 
 const ID: &str = "layer.setEffectsExpanded";
 
+/// A `layer.setEffectsExpanded` parameter error.
 fn bad(msg: impl Into<String>) -> EngineError {
     EngineError::BadParams { cmd: ID.into(), msg: msg.into() }
 }
 
+/// The command is available while some layer has effects or Smart Filters to disclose.
 fn has_effects(s: &Session) -> std::result::Result<(), String> {
     let d = s.active().ok_or("no document open")?;
     if d.doc.walk().iter().any(|(_, _, l)| has_children(l)) { Ok(()) } else { Err("no layer has effects or smart filters".into()) }
@@ -24,6 +26,7 @@ fn has_children(l: &Layer) -> bool {
     !l.effects.items.is_empty() || matches!(&l.content, LayerContent::Smart(sm) if !sm.smart_filters.is_empty())
 }
 
+/// An optional boolean param: `None` when absent or null, an error when it is anything but true or false.
 fn opt_bool(p: &Value, key: &str) -> Result<Option<bool>> {
     match p.get(key) {
         None | Some(Value::Null) => Ok(None),
@@ -64,6 +67,7 @@ fn set_expanded(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({"expanded": expanded, "layers": targets.len()}))
 }
 
+/// Register `layer.setEffectsExpanded`: view state, so it is not journaled and adds no undo step.
 pub fn specs() -> Vec<CommandSpec> {
     vec![CommandSpec {
         id: ID,
@@ -93,6 +97,7 @@ mod tests {
         (s, a, b)
     }
 
+    /// Whether the layer's effects list is shown, i.e. it is not in the document's collapsed set.
     fn open(s: &Session, id: u64) -> bool {
         !s.active().unwrap().fx_collapsed.contains(&LayerId(id))
     }
@@ -120,6 +125,7 @@ mod tests {
         assert!(s.active().unwrap().fx_collapsed.is_empty());
     }
 
+    /// Toggling one layer or all of them flips only the disclosure state: no history step, no duplicates, and the document stays clean.
     #[test]
     fn toggles_one_layer_or_all_without_history() {
         let (mut s, a, b) = session();
diff --git a/crates/engine/src/smart_cmds/tests.rs b/crates/engine/src/smart_cmds/tests.rs
index 3666a4818c..f955a21ee5 100644
--- a/crates/engine/src/smart_cmds/tests.rs
+++ b/crates/engine/src/smart_cmds/tests.rs
@@ -77,6 +77,7 @@ fn non_normal_coverage_changes_retain_source_over_semantics() {
     }
 }
 
+/// A `depth`-bit document with one empty layer.
 fn session(depth: u64) -> Session {
     let mut s = Session::new();
     s.execute("file.new", json!({"width": W, "height": H, "depth": depth})).unwrap();
diff --git a/crates/engine/tests/photoshop_oracles.rs b/crates/engine/tests/photoshop_oracles.rs
index 1b3e37d3e9..b1f0a133a1 100644
--- a/crates/engine/tests/photoshop_oracles.rs
+++ b/crates/engine/tests/photoshop_oracles.rs
@@ -93,6 +93,7 @@ fn screen_motion_blur_retains_input_coverage() {
     assert!(error <= PASS_TOL, "Screen/Motion Blur error {error}, {bad}% pixels exceed 2/255");
 }
 
+/// Re-render every Photoshop oracle in the corpus with PhotoCraft's filters and compare it with Photoshop's own merged composite.
 #[test]
 fn photoshop_oracles_rerendered() {
     let root = Path::new(env!("CARGO_MANIFEST_DIR")).join("../../corpus/photoshop");
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 584d0928df..893401ba85 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -2330,6 +2330,7 @@ impl PhotocraftApp {
         id
     }
 
+    /// The cached thumbnail of `mask`, the layer mask of layer `id`.
     pub fn mask_thumb(&mut self, ctx: &egui::Context, doc: &Document, id: photocraft_doc::LayerId, mask: &photocraft_doc::LayerMask) -> egui::TextureId {
         self.mask_thumb_kind(ctx, doc, id, mask, mask_thumbs_ui::THUMB_MASK)
     }
diff --git a/crates/ui-egui/src/smart_ui.rs b/crates/ui-egui/src/smart_ui.rs
index 1d8e6d68ce..8afc3578ea 100644
--- a/crates/ui-egui/src/smart_ui.rs
+++ b/crates/ui-egui/src/smart_ui.rs
@@ -206,6 +206,7 @@ pub fn filter_rows(app: &mut PhotocraftApp, ui: &mut egui::Ui, doc: &Document, l
 /// Filters row, all of them). Also what a click selects.
 pub(crate) type FilterDrag = (u64, Option<usize>);
 
+/// Memory key of the smart filter row being dragged.
 pub(crate) fn drag_key() -> egui::Id {
     egui::Id::new("smart-filter-drag")
 }