diff --git a/crates/engine/src/cmd/edit.rs b/crates/engine/src/cmd/edit.rs
index 30437b15..229296c0 100644
--- a/crates/engine/src/cmd/edit.rs
+++ b/crates/engine/src/cmd/edit.rs
@@ -48,7 +48,7 @@ fn slides_scope(s: &Session, p: &Value) -> bool {
         || s.active().is_some_and(|d| d.selection.shapes.is_empty() && d.selection.text.is_none() && !d.selection.slides.is_empty())
 }
 
-fn media_of_shapes(shapes: &[Shape], out: &mut Vec<MediaId>) {
+pub(crate) fn media_of_shapes(shapes: &[Shape], out: &mut Vec<MediaId>) {
     deckcraft_model::walk(shapes, &mut |s, _| {
         match &s.kind {
             deckcraft_model::ShapeKind::Picture { fill } => out.push(fill.media),
diff --git a/crates/engine/src/cmd/review.rs b/crates/engine/src/cmd/review.rs
index 8e3a532c..b9f25d40 100644
--- a/crates/engine/src/cmd/review.rs
+++ b/crates/engine/src/cmd/review.rs
@@ -16,6 +16,10 @@ pub fn specs() -> Vec<CommandSpec> {
         cmd!("comment.resolve", "Resolve Thread", ["Comments"], None, "{index, resolved?: bool}", has_slide, resolve),
         cmd!(query "comment.list", "Comments", [], None, "{slide?} → comments", has_slide, list),
         cmd!(query "review.accessibility", "Check Accessibility", ["Review", "Accessibility"], None, "{} → [{slide, shape, issue}]", has_doc, accessibility),
+        cmd!(noundo "review.compare", "Compare", ["Review", "Compare"], None, "{path} | {name, data: base64} — compare with a revised copy → {name, changes}", has_doc, compare),
+        cmd!(query "review.revisions", "Revisions", [], None, "{} → {name, changes: [{kind: inserted|deleted|changed, slide, revised, details}]}", has_doc, revisions),
+        cmd!("review.accept", "Accept Revision", ["Review", "Compare"], None, "{index} | {all: true}", comparing, accept),
+        cmd!(noundo "review.endCompare", "End Review", ["Review", "Compare"], None, "{}", comparing, end_compare),
         cmd!(query "review.spelling", "Spelling", ["Review", "Proofing"], Some("F7"), "{} → [{slide, shape, word}] (words not in the built-in list)", has_doc, spelling),
         cmd!(noundo "show.fromStart", "Play from Start", ["Slide Show", "Start Slide Show"], Some("Cmd+Shift+Enter"), "{}", has_slide, |s, _| start(s, 0)),
         cmd!(noundo "show.fromCurrent", "Play from Current Slide", ["Slide Show", "Start Slide Show"], Some("Cmd+Enter"), "{}", has_slide, |s, _| {
@@ -264,3 +268,80 @@ fn custom_show(s: &mut Session, p: &Value) -> Result<Value> {
     })?;
     ok()
 }
+
+fn comparing(s: &Session) -> std::result::Result<(), String> {
+    if s.active().is_some_and(|d| d.compare.is_some()) { Ok(()) } else { Err("not comparing".into()) }
+}
+
+fn revised_bytes(p: &Value) -> Result<(String, Vec<u8>)> {
+    if let Some(data) = str_param(p, "data") {
+        let bytes = base64_decode(data).ok_or_else(|| bad("review.compare", "invalid base64 `data`"))?;
+        return Ok((str_param(p, "name").unwrap_or("Revised").to_string(), bytes));
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    if let Some(path) = str_param(p, "path") {
+        let bytes = std::fs::read(path).map_err(|e| crate::EngineError::Other(format!("{path}: {e}")))?;
+        return Ok((path.to_string(), bytes));
+    }
+    Err(bad("review.compare", "give `path` or `data`"))
+}
+
+fn revisions_json(st: &crate::DocState) -> Result<Value> {
+    let c = st.compare.as_ref().ok_or_else(|| bad("review.revisions", "not comparing"))?;
+    let name = std::path::Path::new(&c.name).file_name().map(|n| n.to_string_lossy().to_string()).unwrap_or_else(|| c.name.clone());
+    Ok(json!({"name": name, "changes": crate::compare::diff(&st.doc, &c.revised, c.by_position), "byPosition": c.by_position}))
+}
+
+fn compare(s: &mut Session, p: &Value) -> Result<Value> {
+    let (name, bytes) = revised_bytes(p)?;
+    let revised = super::file::open_presentation(&name, &bytes)?;
+    let st = s.doc_mut()?;
+    let by_position = crate::compare::unrelated(&st.doc, &revised);
+    st.compare = Some(crate::compare::Compare { name, revised: Arc::new(revised), by_position });
+    s.ui_requests.push(UiRequest::Pane { id: "revisions".into() });
+    revisions_json(s.doc()?)
+}
+
+fn revisions(s: &mut Session, _: &Value) -> Result<Value> {
+    revisions_json(s.doc()?)
+}
+
+fn accept(s: &mut Session, p: &Value) -> Result<Value> {
+    let (rev, by_pos) = s.doc()?.compare.as_ref().map(|c| (c.revised.clone(), c.by_position)).ok_or_else(|| bad("review.accept", "not comparing"))?;
+    let all = bool_param(p, "all").unwrap_or(false);
+    let index = usize_param(p, "index");
+    if !all && index.is_none() {
+        return Err(bad("review.accept", "give `index` or `all`"));
+    }
+    s.edit(|doc, sel| {
+        let mut accepted = 0usize;
+        // Each accept shifts indices, so the list is recomputed; bounded by the slide counts.
+        let limit = doc.slides.len().saturating_add(rev.slides.len()).saturating_add(1);
+        for _ in 0..limit {
+            let changes = crate::compare::diff(doc, &rev, by_pos);
+            let c = if all {
+                changes.into_iter().find(|c| !(c.kind == crate::compare::ChangeKind::Deleted && doc.slides.len() <= 1))
+            } else {
+                changes.into_iter().nth(index.unwrap_or(0))
+            };
+            let Some(c) = c else { break };
+            let Some(at) = crate::compare::accept(doc, &rev, &c) else { break };
+            accepted += 1;
+            sel.slide = at;
+            sel.shapes.clear();
+            sel.text = None;
+            if !all {
+                break;
+            }
+        }
+        if accepted == 0 {
+            return Err(bad("review.accept", "no such revision"));
+        }
+        Ok(json!({"accepted": accepted}))
+    })
+}
+
+fn end_compare(s: &mut Session, _: &Value) -> Result<Value> {
+    s.doc_mut()?.compare = None;
+    ok()
+}
diff --git a/crates/engine/src/compare.rs b/crates/engine/src/compare.rs
new file mode 100644
index 00000000..5d65c0cc
--- /dev/null
+++ b/crates/engine/src/compare.rs
@@ -0,0 +1,449 @@
+//! Review › Compare: the differences between the open presentation and a revised copy of it, slide
+//! by slide, and accepting a revised slide into the open one.
+//!
+//! Slides match by id (a revised copy of the same deck keeps them); when the two decks share no
+//! slide id at all, by position. Shapes match by id, then by name.
+
+use std::collections::{HashMap, HashSet};
+use std::sync::Arc;
+
+use deckcraft_model::{Fill, MediaId, Presentation, Shape, ShapeId, ShapeKind, Slide, SlideId};
+use serde::Serialize;
+
+/// The revised presentation a document is being compared with.
+#[derive(Clone, Debug)]
+pub struct Compare {
+    pub name: String,
+    pub revised: Arc<Presentation>,
+    /// Slides match by position (the decks shared no slide id when the compare started); fixed
+    /// for the session so accepting slides doesn't switch the matching half way.
+    pub by_position: bool,
+}
+
+/// Whether `cur` and `rev` share no slide id (then slides match by position).
+pub fn unrelated(cur: &Presentation, rev: &Presentation) -> bool {
+    let ids: HashSet<SlideId> = rev.slides.iter().map(|s| s.id).collect();
+    !cur.slides.iter().any(|s| ids.contains(&s.id))
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ChangeKind {
+    /// Only in the revised deck.
+    Inserted,
+    /// Only in the open deck.
+    Deleted,
+    /// In both, different.
+    Changed,
+}
+
+/// One slide-level revision.
+#[derive(Clone, Debug, PartialEq, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Change {
+    pub kind: ChangeKind,
+    /// Index in the open deck (for inserted: where it would go).
+    pub slide: usize,
+    /// Index in the revised deck (none for deleted).
+    pub revised: Option<usize>,
+    /// What differs, readable: `Title 1: text`, `Picture 3 inserted`, `notes`…
+    pub details: Vec<String>,
+}
+
+const MAX_DETAILS: usize = 50;
+
+/// Slide pairs (open index, revised index).
+fn pairs(cur: &Presentation, rev: &Presentation, by_position: bool) -> Vec<(usize, usize)> {
+    if by_position {
+        return (0..cur.slides.len().min(rev.slides.len())).map(|i| (i, i)).collect();
+    }
+    let rev_ids: HashMap<SlideId, usize> = rev.slides.iter().enumerate().map(|(i, s)| (s.id, i)).collect();
+    cur.slides.iter().enumerate().filter_map(|(i, s)| rev_ids.get(&s.id).map(|j| (i, *j))).collect()
+}
+
+pub fn diff(cur: &Presentation, rev: &Presentation, by_position: bool) -> Vec<Change> {
+    let pairs = pairs(cur, rev, by_position);
+    let cur_matched: HashSet<usize> = pairs.iter().map(|p| p.0).collect();
+    let rev_matched: HashSet<usize> = pairs.iter().map(|p| p.1).collect();
+    let mut out = vec![];
+    for (i, j) in &pairs {
+        let (Some(a), Some(b)) = (cur.slides.get(*i), rev.slides.get(*j)) else { continue };
+        let details = slide_details(cur, a, rev, b);
+        if !details.is_empty() {
+            out.push(Change { kind: ChangeKind::Changed, slide: *i, revised: Some(*j), details });
+        }
+    }
+    for (i, s) in cur.slides.iter().enumerate() {
+        if !cur_matched.contains(&i) {
+            out.push(Change { kind: ChangeKind::Deleted, slide: i, revised: None, details: vec![slide_title(s)] });
+        }
+    }
+    for (j, s) in rev.slides.iter().enumerate() {
+        if !rev_matched.contains(&j) {
+            // After the open slide that matches the revised slide before it.
+            let at = (0..j).rev().find_map(|k| pairs.iter().find(|p| p.1 == k).map(|p| p.0 + 1)).unwrap_or(0);
+            out.push(Change { kind: ChangeKind::Inserted, slide: at, revised: Some(j), details: vec![slide_title(s)] });
+        }
+    }
+    out.sort_by_key(|c| (c.slide, c.revised.unwrap_or(0)));
+    out
+}
+
+fn slide_title(s: &Slide) -> String {
+    let t = s
+        .shapes
+        .iter()
+        .find(|x| x.ph.as_ref().is_some_and(|p| matches!(p.kind, deckcraft_model::PhType::Title | deckcraft_model::PhType::CtrTitle)))
+        .and_then(|x| x.text.as_ref())
+        .map(|b| b.text())
+        .unwrap_or_default();
+    let t = t.trim();
+    if t.is_empty() { "Untitled slide".into() } else { t.chars().take(60).collect() }
+}
+
+fn shape_label(s: &Shape) -> String {
+    if s.name.trim().is_empty() { format!("Shape {}", s.id.0) } else { s.name.clone() }
+}
+
+fn media_bytes(p: &Presentation, id: MediaId) -> Option<&[u8]> {
+    p.media(id).map(|m| m.data.as_slice())
+}
+
+/// A shape without its ids (shape and media), for comparing across decks.
+fn plain_shape(s: &Shape) -> Shape {
+    let mut c = s.clone();
+    fn rec(shapes: &mut [Shape]) {
+        for s in shapes {
+            s.id = ShapeId(0);
+            if let Some(ch) = s.children_mut() {
+                rec(ch);
+            }
+        }
+    }
+    rec(std::slice::from_mut(&mut c));
+    c
+}
+
+fn shape_details(cp: &Presentation, a: &Shape, rp: &Presentation, b: &Shape, out: &mut Vec<String>) {
+    let label = shape_label(b);
+    let text = |s: &Shape| s.text.as_ref().map(|t| t.text()).unwrap_or_default();
+    let mut what = vec![];
+    if text(a) != text(b) {
+        what.push("text");
+    } else if a.text != b.text {
+        what.push("text formatting");
+    }
+    match (&a.xfrm, &b.xfrm) {
+        (Some(x), Some(y)) if (x.x, x.y) != (y.x, y.y) && (x.w, x.h) == (y.w, y.h) => what.push("moved"),
+        (Some(x), Some(y)) if (x.w, x.h) != (y.w, y.h) => what.push("resized"),
+        (x, y) if x.as_ref().map(|x| x.rot) != y.as_ref().map(|y| y.rot) => what.push("rotated"),
+        _ => {}
+    }
+    if a.fill != b.fill || a.line != b.line || a.style != b.style || a.effects != b.effects {
+        what.push("formatting");
+    }
+    let pic = |p: &Presentation, s: &Shape| match &s.kind {
+        ShapeKind::Picture { fill } => media_bytes(p, fill.media).map(|b| b.to_vec()),
+        _ => None,
+    };
+    if pic(cp, a) != pic(rp, b) {
+        what.push("picture");
+    }
+    if what.is_empty() {
+        let (mut x, mut y) = (plain_shape(a), plain_shape(b));
+        x.text = None;
+        y.text = None;
+        if let (ShapeKind::Picture { .. }, ShapeKind::Picture { .. }) = (&x.kind, &y.kind) {
+            x.kind = ShapeKind::Shape;
+            y.kind = ShapeKind::Shape;
+        }
+        if x != y {
+            what.push("properties");
+        }
+    }
+    if !what.is_empty() {
+        out.push(format!("{label}: {}", what.join(", ")));
+    }
+}
+
+fn slide_details(cp: &Presentation, a: &Slide, rp: &Presentation, b: &Slide) -> Vec<String> {
+    let mut out = vec![];
+    let mut used: HashSet<usize> = HashSet::new();
+    for sa in &a.shapes {
+        let k = b
+            .shapes
+            .iter()
+            .position(|x| x.id == sa.id)
+            .or_else(|| b.shapes.iter().enumerate().position(|(k, x)| !used.contains(&k) && x.name == sa.name && !x.name.is_empty()));
+        match k {
+            Some(k) if !used.contains(&k) => {
+                used.insert(k);
+                if let Some(sb) = b.shapes.get(k) {
+                    shape_details(cp, sa, rp, sb, &mut out);
+                }
+            }
+            _ => out.push(format!("{} deleted", shape_label(sa))),
+        }
+    }
+    for (k, sb) in b.shapes.iter().enumerate() {
+        if !used.contains(&k) {
+            out.push(format!("{} inserted", shape_label(sb)));
+        }
+    }
+    let order = |s: &Slide| s.shapes.iter().map(|x| x.name.clone()).collect::<Vec<_>>();
+    if out.is_empty() && order(a) != order(b) {
+        out.push("order of objects".into());
+    }
+    let layout_name = |p: &Presentation, s: &Slide| p.layout(s.layout).map(|(_, l)| l.name.clone());
+    if layout_name(cp, a) != layout_name(rp, b) {
+        out.push("layout".into());
+    }
+    if a.notes.text() != b.notes.text() {
+        out.push("notes".into());
+    }
+    if a.transition != b.transition {
+        out.push("transition".into());
+    }
+    if a.animations.len() != b.animations.len()
+        || a.animations
+            .iter()
+            .zip(&b.animations)
+            .any(|(x, y)| (&x.effect, x.class, x.start, x.duration_ms, x.delay_ms) != (&y.effect, y.class, y.start, y.duration_ms, y.delay_ms))
+    {
+        out.push("animations".into());
+    }
+    if a.background != b.background {
+        out.push("background".into());
+    }
+    if a.hidden != b.hidden {
+        out.push(if b.hidden { "hidden" } else { "shown" }.into());
+    }
+    out.truncate(MAX_DETAILS);
+    out
+}
+
+fn max_shape_id(shapes: &[Shape], m: &mut u32) {
+    deckcraft_model::walk(shapes, &mut |s, _| *m = (*m).max(s.id.0));
+}
+
+/// The revised slide made to live in `doc`: its media copied over (remapped on an id clash), shape
+/// ids kept unless another slide of `doc` uses them (then fresh, animations following), and its
+/// layout matched by id, then by name, then the first layout.
+pub fn adopt(doc: &mut Presentation, rev: &Presentation, slide: &Slide, replacing: Option<SlideId>) -> Slide {
+    let mut sl = slide.clone();
+    // Media.
+    let mut mids = vec![];
+    crate::cmd::edit::media_of_shapes(&sl.shapes, &mut mids);
+    let mut media_map: HashMap<MediaId, MediaId> = HashMap::new();
+    for id in mids {
+        let Some(m) = rev.media(id) else { continue };
+        match doc.media(id) {
+            Some(x) if x.data == m.data => {}
+            None => doc.media.push(m.clone()),
+            Some(_) => {
+                let new = doc.add_media(&m.name, &m.content_type, m.data.as_ref().clone());
+                media_map.insert(id, new);
+            }
+        }
+    }
+    // Shape ids used elsewhere in the open deck.
+    let mut taken: HashSet<u32> = HashSet::new();
+    for s in doc.slides.iter().filter(|s| Some(s.id) != replacing) {
+        deckcraft_model::walk(&s.shapes, &mut |x, _| {
+            taken.insert(x.id.0);
+        });
+    }
+    let mut id_map: HashMap<ShapeId, ShapeId> = HashMap::new();
+    fn rec(
+        doc: &mut Presentation,
+        shapes: &mut [Shape],
+        taken: &HashSet<u32>,
+        ids: &mut HashMap<ShapeId, ShapeId>,
+        media: &HashMap<MediaId, MediaId>,
+        depth: usize,
+    ) {
+        if depth > 64 {
+            return;
+        }
+        for s in shapes {
+            if taken.contains(&s.id.0) {
+                let new = ShapeId(doc.alloc_id());
+                ids.insert(s.id, new);
+                s.id = new;
+            }
+            let remap = |m: &mut MediaId| {
+                if let Some(n) = media.get(m) {
+                    *m = *n;
+                }
+            };
+            match &mut s.kind {
+                ShapeKind::Picture { fill } => remap(&mut fill.media),
+                ShapeKind::Media(m) => {
+                    remap(&mut m.media);
+                    if let Some(p) = m.poster.as_mut() {
+                        remap(p);
+                    }
+                }
+                _ => {}
+            }
+            if let Some(Fill::Picture(pf)) = &mut s.fill {
+                remap(&mut pf.media);
+            }
+            if let Some(ch) = s.children_mut() {
+                rec(doc, ch, taken, ids, media, depth + 1);
+            }
+        }
+    }
+    rec(doc, &mut sl.shapes, &taken, &mut id_map, &media_map, 0);
+    for a in &mut sl.animations {
+        if let Some(n) = id_map.get(&a.shape) {
+            a.shape = *n;
+        }
+        if let Some(t) = a.trigger.as_mut()
+            && let Some(n) = id_map.get(t)
+        {
+            *t = *n;
+        }
+    }
+    let mut max = 0;
+    max_shape_id(&sl.shapes, &mut max);
+    doc.next_id = doc.next_id.max(max);
+    // Layout.
+    if doc.layout(sl.layout).is_none() {
+        let name = rev.layout(slide.layout).map(|(_, l)| l.name.clone());
+        let by_name = name.and_then(|n| doc.masters.iter().flat_map(|m| &m.layouts).find(|l| l.name == n).map(|l| l.id));
+        sl.layout = by_name.or_else(|| doc.masters.first().and_then(|m| m.layouts.first()).map(|l| l.id)).unwrap_or_default();
+    }
+    match replacing {
+        Some(id) => sl.id = id,
+        None => {
+            if doc.slides.iter().any(|s| s.id == sl.id) || sl.id.0 == 0 {
+                sl.id = SlideId(doc.alloc_id());
+            }
+            doc.next_id = doc.next_id.max(sl.id.0);
+        }
+    }
+    sl
+}
+
+/// Apply `change` (from [`diff`] of `doc` against `rev`) to `doc`. Returns the slide index to show.
+pub fn accept(doc: &mut Presentation, rev: &Presentation, change: &Change) -> Option<usize> {
+    match change.kind {
+        ChangeKind::Changed => {
+            let b = rev.slides.get(change.revised?)?.clone();
+            let id = doc.slides.get(change.slide)?.id;
+            let sl = adopt(doc, rev, &b, Some(id));
+            *doc.slides.get_mut(change.slide)? = Arc::new(sl);
+            Some(change.slide)
+        }
+        ChangeKind::Inserted => {
+            let b = rev.slides.get(change.revised?)?.clone();
+            let sl = adopt(doc, rev, &b, None);
+            let at = change.slide.min(doc.slides.len());
+            doc.slides.insert(at, Arc::new(sl));
+            Some(at)
+        }
+        ChangeKind::Deleted => {
+            if change.slide >= doc.slides.len() || doc.slides.len() <= 1 {
+                return None;
+            }
+            doc.slides.remove(change.slide);
+            Some(change.slide.min(doc.slides.len().saturating_sub(1)))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::{Value, json};
+
+    use crate::Session;
+
+    /// The sample deck, and a revised copy of it as base64 `.deckcraft` bytes: slide 1's title
+    /// retyped, slide 2 deleted, a new slide at the end, a shape moved on slide 3.
+    fn decks() -> (Session, String, usize) {
+        let mut s = Session::new();
+        crate::sample::open_sample(&mut s).unwrap();
+        let n = s.doc().unwrap().doc.slides.len();
+        let orig = s.execute("file.saveBytes", &json!({})).unwrap()["data"].as_str().unwrap().to_string();
+        // Make the revision in a second document.
+        s.execute("file.openBytes", &json!({"name": "rev.deckcraft", "data": orig})).unwrap();
+        let first = s.doc().unwrap().doc.slides[0].shapes.iter().find(|x| x.text.is_some()).unwrap().id.0;
+        s.execute("edit.select", &json!({"ids": [first]})).unwrap();
+        s.execute("text.edit", &json!({"id": first})).unwrap();
+        s.execute("edit.selectAll", &json!({})).unwrap();
+        s.execute("text.insert", &json!({"text": "Revised title"})).unwrap();
+        s.execute("text.exit", &json!({})).unwrap();
+        s.execute("slide.delete", &json!({"index": 1})).unwrap();
+        s.execute("slide.go", &json!({"index": 1})).ok();
+        let moved = s.doc().unwrap().doc.slides[1].shapes[0].id.0;
+        s.execute("shape.move", &json!({"ids": [moved], "dx": 30, "dy": 0})).ok();
+        s.execute("slide.go", &json!({"index": n - 2})).ok();
+        s.execute("slide.new", &json!({"layout": "titleAndContent", "title": "Brand new", "body": "x"})).unwrap();
+        let rev = s.execute("file.saveBytes", &json!({})).unwrap()["data"].as_str().unwrap().to_string();
+        s.close_document(1);
+        s.set_active(0);
+        (s, rev, n)
+    }
+
+    fn kinds(v: &Value) -> Vec<String> {
+        v["changes"].as_array().unwrap().iter().map(|c| c["kind"].as_str().unwrap().to_string()).collect()
+    }
+
+    #[test]
+    fn lists_inserted_deleted_and_changed_slides() {
+        let (mut s, rev, n) = decks();
+        let v = s.execute("review.compare", &json!({"name": "rev.deckcraft", "data": rev})).unwrap();
+        let k = kinds(&v);
+        assert!(k.contains(&"deleted".into()) && k.contains(&"inserted".into()) && k.contains(&"changed".into()), "{v}");
+        let ch = &v["changes"].as_array().unwrap()[0];
+        assert_eq!(ch["slide"], 0);
+        assert!(ch["details"].to_string().contains("text"), "{ch}");
+        let ins = v["changes"].as_array().unwrap().iter().find(|c| c["kind"] == "inserted").unwrap();
+        assert_eq!(ins["details"][0], "Brand new");
+        let at = ins["slide"].as_u64().unwrap() as usize;
+        assert_eq!(at, n, "after the open slide matching the revised one before it");
+        assert_eq!(s.doc().unwrap().doc.slides.len(), n, "comparing alone changes nothing");
+    }
+
+    #[test]
+    fn accept_one_then_all_makes_the_decks_equal_and_undoes() {
+        let (mut s, rev, n) = decks();
+        s.execute("review.compare", &json!({"name": "rev.deckcraft", "data": rev})).unwrap();
+        let before = s.execute("review.revisions", &json!({})).unwrap()["changes"].as_array().unwrap().len();
+        s.execute("review.accept", &json!({"index": 0})).unwrap();
+        let after = s.execute("review.revisions", &json!({})).unwrap()["changes"].as_array().unwrap().len();
+        assert_eq!(after, before - 1);
+        assert!(s.doc().unwrap().doc.slides[0].shapes.iter().any(|x| x.text.as_ref().is_some_and(|t| t.text().contains("Revised title"))));
+        s.execute("review.accept", &json!({"all": true})).unwrap();
+        let left = s.execute("review.revisions", &json!({})).unwrap();
+        assert!(left["changes"].as_array().unwrap().is_empty(), "{left}");
+        assert!(s.doc().unwrap().doc.validate().is_empty(), "{:?}", s.doc().unwrap().doc.validate());
+        assert_eq!(s.doc().unwrap().doc.slides.len(), n);
+        s.execute("edit.undo", &json!({})).unwrap();
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(s.execute("review.revisions", &json!({})).unwrap()["changes"].as_array().unwrap().len(), before);
+        s.execute("review.endCompare", &json!({})).unwrap();
+        assert!(s.execute("review.revisions", &json!({})).is_err());
+        assert!(s.execute("review.accept", &json!({"all": true})).is_err());
+    }
+
+    #[test]
+    fn unrelated_decks_match_by_position_and_bad_input_fails() {
+        let mut s = Session::with_new();
+        s.execute("slide.new", &json!({"layout": "title", "title": "A"})).unwrap();
+        let mut other = Session::with_new();
+        other.execute("slide.new", &json!({"layout": "title", "title": "B"})).unwrap();
+        other.execute("slide.new", &json!({"layout": "title", "title": "C"})).unwrap();
+        let data = other.execute("file.saveBytes", &json!({"format": "pptx"})).unwrap()["data"].as_str().unwrap().to_string();
+        let v = s.execute("review.compare", &json!({"name": "o.pptx", "data": data})).unwrap();
+        assert!(kinds(&v).contains(&"inserted".into()), "{v}");
+        s.execute("review.accept", &json!({"all": true})).unwrap();
+        assert!(s.execute("review.revisions", &json!({})).unwrap()["changes"].as_array().unwrap().is_empty());
+        assert!(s.doc().unwrap().doc.validate().is_empty());
+        assert!(s.execute("review.compare", &json!({"data": "!!"})).is_err());
+        assert!(s.execute("review.compare", &json!({"name": "x.bin", "data": "AAAA"})).is_err());
+        assert!(s.execute("review.compare", &json!({})).is_err());
+        assert!(s.execute("review.accept", &json!({"index": 999})).is_err());
+    }
+}
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index c2b56c7f..2c4df3cd 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -8,6 +8,7 @@
 #![forbid(unsafe_code)]
 
 pub mod cmd;
+pub mod compare;
 pub mod connect;
 pub mod fonts;
 pub mod guard;
@@ -173,6 +174,8 @@ pub struct DocState {
     pub missing_fonts: Vec<String>,
     /// An input method's composition in progress ([`Composition`]).
     pub composition: Option<Composition>,
+    /// Review › Compare in progress: the revised copy.
+    pub compare: Option<compare::Compare>,
 }
 
 static NEXT_UID: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(1);
@@ -192,6 +195,7 @@ impl DocState {
             title,
             missing_fonts: Vec::new(),
             composition: None,
+            compare: None,
         }
     }
     pub fn is_dirty(&self) -> bool {
diff --git a/crates/ui-egui/src/compare_tests.rs b/crates/ui-egui/src/compare_tests.rs
new file mode 100644
index 00000000..9108b4de
--- /dev/null
+++ b/crates/ui-egui/src/compare_tests.rs
@@ -0,0 +1,61 @@
+//! Review › Compare: the Revisions pane lists a revised copy's changes and accepts them.
+
+use deckcraft_engine::Session;
+use egui_kittest::Harness;
+use egui_kittest::kittest::Queryable;
+use serde_json::json;
+
+use crate::{Services, SlideApp};
+
+/// The sample deck compared with a copy whose slide 2 is gone and that has a new last slide.
+fn harness() -> (Harness<'static, SlideApp>, usize) {
+    let mut s = Session::new();
+    deckcraft_engine::sample::open_sample(&mut s).unwrap();
+    let n = s.doc().unwrap().doc.slides.len();
+    let data = s.execute("file.saveBytes", &json!({})).unwrap()["data"].as_str().unwrap().to_string();
+    s.execute("file.openBytes", &json!({"name": "rev.deckcraft", "data": data})).unwrap();
+    s.execute("slide.delete", &json!({"index": 1})).unwrap();
+    s.execute("slide.go", &json!({"index": n - 2})).unwrap();
+    s.execute("slide.new", &json!({"layout": "titleAndContent", "title": "From the reviewer", "body": "x"})).unwrap();
+    let rev = s.execute("file.saveBytes", &json!({})).unwrap()["data"].as_str().unwrap().to_string();
+    s.close_document(1);
+    s.set_active(0);
+    s.execute("review.compare", &json!({"name": "Q3 review.deckcraft", "data": rev})).unwrap();
+    let app = SlideApp::new(s, Services::default());
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).with_step_dt(1.0 / 60.0).build_ui_state(
+        |ui, app: &mut SlideApp| {
+            app.logic(ui.ctx());
+            app.ui(ui);
+        },
+        app,
+    );
+    h.run_steps(4);
+    (h, n)
+}
+
+#[test]
+fn pane_opens_lists_changes_and_accept_all_applies_them() {
+    let (mut h, n) = harness();
+    assert_eq!(h.state().ui.pane.as_deref(), Some("revisions"), "compare opens the Revisions pane");
+    assert!(h.query_by_label("Compared with Q3 review.deckcraft").is_some());
+    assert!(h.query_by_label("Slide 2 deleted").is_some());
+    assert!(h.query_by_label_contains("Slide inserted after").is_some());
+    h.get_by_label_contains("Accept All").click();
+    h.run_steps(3);
+    let st = h.state().session.active().unwrap();
+    assert_eq!(st.doc.slides.len(), n, "one slide gone, one slide added");
+    assert!(h.query_by_label("No differences left.").is_some());
+    h.get_by_label("End Review").click();
+    h.run_steps(3);
+    assert!(h.state().session.active().unwrap().compare.is_none());
+}
+
+#[test]
+#[ignore = "writes a screenshot for review"]
+fn screenshot() {
+    let (mut h, _) = harness();
+    // Review tab.
+    h.state_mut().ui.tab = "Review".into();
+    h.run_steps(4);
+    h.render().unwrap().save("/tmp/compare.png").unwrap();
+}
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index ec97e6e6..9f28b35d 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -167,6 +167,7 @@ pub const UI_COMMANDS: &[(&str, &str, Option<&str>, &str)] = &[
     ("app.insertVideoDialog", "Video from File…", None, "{}"),
     ("app.saveAsDialog", "Save As…", None, "{}"),
     ("app.exportDialog", "Export…", None, "{}"),
+    ("app.compareDialog", "Compare…", None, "{}"),
     ("app.dialog", "Open Dialog", None, "{id}"),
     ("app.links", "Community Links", None, "{}"),
 ];
@@ -541,6 +542,17 @@ impl SlideApp {
             "app.insertVideoDialog" => self.pick_and_insert("video", "insert.video"),
             "app.saveAsDialog" => self.save_as_dialog("deckcraft"),
             "app.exportDialog" => self.dialog = Some(dialogs::Dialog::new("export")),
+            "app.compareDialog" => {
+                if self.session.active().is_none() {
+                    return Err("open the presentation to compare first".into());
+                }
+                if self.services.pick_open.is_some() {
+                    self.pick_and_insert("open", "review.compare");
+                } else {
+                    // The browser's asynchronous picker would open the file as a new document.
+                    self.set_status("Compare needs the desktop app for now".to_string());
+                }
+            }
             "app.dialog" => {
                 let d = p.get("id").and_then(Value::as_str).ok_or("missing `id`")?;
                 self.dialog = Some(dialogs::Dialog::new(d));
@@ -1127,6 +1139,8 @@ fn js_now() -> f64 {
     js_sys::Date::now()
 }
 
+#[cfg(test)]
+mod compare_tests;
 #[cfg(test)]
 mod ime_tests;
 
diff --git a/crates/ui-egui/src/panes.rs b/crates/ui-egui/src/panes.rs
index 2b3ada3a..fac96b69 100644
--- a/crates/ui-egui/src/panes.rs
+++ b/crates/ui-egui/src/panes.rs
@@ -27,6 +27,7 @@ pub fn show(app: &mut SlideApp, ui: &mut Ui) {
                 "selection" => "Selection",
                 "comments" => "Comments",
                 "designer" => "Design Ideas",
+                "revisions" => "Revisions",
                 _ => "Pane",
             };
             ui.horizontal(|ui| {
@@ -50,6 +51,7 @@ pub fn show(app: &mut SlideApp, ui: &mut Ui) {
                 "selection" => crate::selpane::show(app, ui),
                 "comments" => comments(app, ui),
                 "designer" => designer(app, ui),
+                "revisions" => revisions(app, ui),
                 _ => {}
             });
         });
@@ -549,6 +551,61 @@ fn animation(app: &mut SlideApp, ui: &mut Ui) {
     let _ = Stroke::NONE;
 }
 
+/// Review › Compare: the revised copy's slide-level changes; click to go there, Accept to take it.
+fn revisions(app: &mut SlideApp, ui: &mut Ui) {
+    let t = Tokens::get(ui.ctx());
+    let Ok(v) = app.session.execute("review.revisions", &json!({})) else {
+        ui.label(egui::RichText::new("Compare this presentation with a revised copy from Review › Compare.").color(t.text_dim));
+        return;
+    };
+    let changes = v["changes"].as_array().cloned().unwrap_or_default();
+    ui.label(egui::RichText::new(format!("Compared with {}", v["name"].as_str().unwrap_or("?"))).color(t.text_dim));
+    if v["byPosition"].as_bool() == Some(true) {
+        ui.label(egui::RichText::new("Not a copy of this presentation: slides are matched by position.").size(11.0).color(t.text_faint));
+    }
+    ui.add_space(4.0);
+    if changes.is_empty() {
+        ui.label("No differences left.");
+        if ui.button("End Review").clicked() {
+            run(app, "review.endCompare", json!({}));
+            app.ui.pane = None;
+        }
+        return;
+    }
+    if ui.button(format!("Accept All ({})", changes.len())).clicked() {
+        run(app, "review.accept", json!({"all": true}));
+    }
+    ui.separator();
+    for (i, c) in changes.iter().enumerate() {
+        let slide = c["slide"].as_u64().unwrap_or(0);
+        let (head, col) = match c["kind"].as_str().unwrap_or("") {
+            "inserted" => (format!("Slide inserted after {slide}"), Color32::from_rgb(0x2E, 0xA3, 0x6F)),
+            "deleted" => (format!("Slide {} deleted", slide.saturating_add(1)), Color32::from_rgb(0xD8, 0x3F, 0x6B)),
+            _ => (format!("Slide {} changed", slide.saturating_add(1)), Color32::from_rgb(0x2E, 0x6F, 0xD8)),
+        };
+        egui::Frame::NONE.fill(t.chrome).corner_radius(CornerRadius::same(6)).inner_margin(egui::Margin::same(8)).show(ui, |ui| {
+            ui.set_width(ui.available_width());
+            ui.horizontal(|ui| {
+                let (r, _) = ui.allocate_exact_size(vec2(4.0, 16.0), Sense::hover());
+                ui.painter().rect_filled(r, CornerRadius::same(2), col);
+                if ui.link(egui::RichText::new(&head).font(theme::bold(12.5))).clicked() {
+                    let max = app.session.active().map(|d| d.doc.slides.len().saturating_sub(1)).unwrap_or(0);
+                    run(app, "slide.go", json!({"index": (slide as usize).min(max)}));
+                }
+                ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                    if ui.small_button("Accept").clicked() {
+                        run(app, "review.accept", json!({"index": i}));
+                    }
+                });
+            });
+            for d in c["details"].as_array().into_iter().flatten().filter_map(Value::as_str).take(8) {
+                ui.label(egui::RichText::new(format!("• {d}")).size(11.5).color(t.text_dim));
+            }
+        });
+        ui.add_space(4.0);
+    }
+}
+
 fn comments(app: &mut SlideApp, ui: &mut Ui) {
     let t = Tokens::get(ui.ctx());
     if ui.button("+ New Comment").clicked() {
diff --git a/crates/ui-egui/src/ribbon.rs b/crates/ui-egui/src/ribbon.rs
index 428eff0b..e4670704 100644
--- a/crates/ui-egui/src/ribbon.rs
+++ b/crates/ui-egui/src/ribbon.rs
@@ -1791,6 +1791,19 @@ fn review(app: &mut SlideApp, ui: &mut Ui) {
         let _ = r.on_hover_text("Translation needs a language model (not bundled)");
         big(app, ui, Icon::Language, "Language", "app.dialog", json!({"id": "language"}));
     });
+    group(ui, |ui| {
+        big(app, ui, Icon::Compare, "Compare", "app.compareDialog", json!({}));
+        let comparing = enabled(app, "review.endCompare");
+        if big_button(ui, Icon::Check, "Accept\nAll", comparing).clicked() {
+            run(app, "review.accept", json!({"all": true}));
+        }
+        if big_button(ui, Icon::Close, "End\nReview", comparing).clicked() {
+            run(app, "review.endCompare", json!({}));
+            if app.ui.pane.as_deref() == Some("revisions") {
+                app.ui.pane = None;
+            }
+        }
+    });
     group(ui, |ui| {
         big(app, ui, Icon::NewComment, "New\nComment", "app.dialog", json!({"id": "comment"}));
         big(app, ui, Icon::DeleteComment, "Delete", "comment.delete", json!({}));
diff --git a/docs/gaps.md b/docs/gaps.md
index a2894b42..5188f10c 100644
--- a/docs/gaps.md
+++ b/docs/gaps.md
@@ -187,7 +187,8 @@ Detail in [animation-parity.md](animation-parity.md). 10–16 h; the pane is a *
 Zoom (summary/section/slide, 6–10 h), reuse slides (2–4 h), laser pointer (1–2 h), transition
 sounds (1–2 h), artistic effects (6–10 h), remove background (6–10 h; needs a model or a classical
 matte), compress pictures (2–3 h), insert screenshot (2–3 h), record audio/screen and record slide
-show (8–12 h), compare presentations (6–10 h), password protection (4–6 h, ECMA-376 agile
+show (8–12 h), compare presentations beyond slide-level accept (reject, per-object accept,
+markers on the slide: 3–5 h), password protection (4–6 h, ECMA-376 agile
 encryption), ink to shape/text (6–10 h), icons and 3-D models (8–14 h, needs an open icon set).
 
 ## UI/UX
diff --git a/docs/parity-checklist.md b/docs/parity-checklist.md
index 2a3d450c..f00fa766 100644
--- a/docs/parity-checklist.md
+++ b/docs/parity-checklist.md
@@ -9,7 +9,7 @@ The summary between `<!-- SUMMARY -->
 |---|---|---|---|---|---|
 | P0 | 72 | 61 | 11 | 0 | 92% |
 | P1 | 65 | 38 | 21 | 6 | 75% |
-| P2 | 54 | 13 | 15 | 26 | 38% |
+| P2 | 54 | 13 | 16 | 25 | 39% |
 
 | Area | Parity |
 |---|---|
@@ -30,7 +30,7 @@ The summary between `<!-- SUMMARY -->
 | Transitions | 92% |
 | Animations | 79% |
 | Slide show | 66% |
-| Review | 60% |
+| Review | 70% |
 | Draw | 33% |
 | Undo & clipboard | 88% |
 | Automation (✱) | 100% |
@@ -221,7 +221,7 @@ Open P0 items: Contextual tabs (Shape Format, Picture Format, Table Design/Layou
 | Slide show | Multi-monitor presenting | P1 | M |
 | Review | Comments (add, reply, resolve, delete) | P1 | D |
 | Review | Accessibility checker | P2 | D |
-| Review | Compare presentations | P2 | M |
+| Review | Compare presentations | P2 | P |
 | Review | Track changes / version history | P2 | M |
 | Draw | Ink pens, highlighter, eraser | P1 | P |
 | Draw | Ink to shape / text | P2 | M |