diff --git a/gpx-rs/engine/src/core/gpx/segment.rs b/gpx-rs/engine/src/core/gpx/segment.rs
index f06aeb30f..fe6ebdf83 100644
--- a/gpx-rs/engine/src/core/gpx/segment.rs
+++ b/gpx-rs/engine/src/core/gpx/segment.rs
@@ -32,12 +32,77 @@ pub struct TrackSegment {
 
 impl TrackSegment {
     pub fn push(&mut self, chunk: TrackpointChunk) {
+        self.push_shared(Rc::new(chunk));
+    }
+
+    fn push_shared(&mut self, chunk: Rc<TrackpointChunk>) {
         if chunk.trkpt.is_empty() {
             return;
         }
         self.cumul_length
             .push(self.cumul_length.last().copied().unwrap_or_default() + chunk.trkpt.len());
-        self.chunks.push(Rc::new(chunk));
+        self.chunks.push(chunk);
+    }
+
+    /// Replaces the points in `start..end` by `points`. Panics if the range is out of bounds.
+    ///
+    /// Chunks that are not concerned are kept as they are (shared), only the chunks around the
+    /// range are copied and refilled.
+    pub fn splice(&mut self, start: usize, end: usize, points: Vec<Trackpoint>) {
+        assert!(
+            start <= end && end <= self.len(),
+            "splice range out of bounds"
+        );
+        let old = std::mem::take(&mut self.chunks);
+        self.cumul_length.clear();
+
+        let mut pending = TrackpointChunk::default();
+        let mut inserted = false;
+        let mut offset = 0;
+        for chunk in old {
+            let (lo, hi) = (offset, offset + chunk.trkpt.len());
+            offset = hi;
+            // a chunk ending at `start` is extended unless it is full, to avoid tiny chunks
+            if hi < start || (hi == start && chunk.is_full()) {
+                self.push_shared(chunk);
+                continue;
+            }
+            if !inserted {
+                self.fill(&mut pending, chunk.trkpt[..start - lo].iter().cloned());
+                self.fill(&mut pending, points.iter().cloned());
+                inserted = true;
+            }
+            if hi <= end {
+                continue;
+            }
+            if lo >= end {
+                self.flush(&mut pending);
+                self.push_shared(chunk);
+            } else {
+                self.fill(&mut pending, chunk.trkpt[end - lo..].iter().cloned());
+            }
+        }
+        if !inserted {
+            self.fill(&mut pending, points);
+        }
+        self.flush(&mut pending);
+    }
+
+    fn fill(
+        &mut self,
+        pending: &mut TrackpointChunk,
+        points: impl IntoIterator<Item = Trackpoint>,
+    ) {
+        for trkpt in points {
+            pending.trkpt.push(trkpt);
+            if pending.is_full() {
+                self.flush(pending);
+            }
+        }
+    }
+
+    fn flush(&mut self, pending: &mut TrackpointChunk) {
+        self.push(std::mem::take(pending));
     }
 
     pub fn len(&self) -> usize {
@@ -193,6 +258,81 @@ mod tests {
         trkseg
     }
 
+    fn eles(trkseg: &TrackSegment) -> Vec<f64> {
+        trkseg.iter().map(|p| p.ele).collect()
+    }
+
+    fn points(eles: &[f64]) -> Vec<Trackpoint> {
+        eles.iter()
+            .map(|&ele| Trackpoint {
+                ele,
+                ..Default::default()
+            })
+            .collect()
+    }
+
+    #[test]
+    fn test_splice_replace_insert_delete_append() {
+        // chunks of 1..=5 points: [0] [1 2] [3 4 5] [6 7 8 9] [10..=14]
+        let mut trkseg = create_track_segment(5);
+        trkseg.splice(4, 8, points(&[-1.0, -2.0]));
+        let mut expected: Vec<f64> = (0..4).map(f64::from).collect();
+        expected.extend([-1.0, -2.0]);
+        expected.extend((8..15).map(f64::from));
+        assert_eq!(eles(&trkseg), expected);
+        assert_eq!(trkseg.len(), expected.len());
+        for i in 0..trkseg.len() {
+            assert_eq!(trkseg[i].ele, expected[i]);
+        }
+
+        trkseg.splice(2, 2, points(&[100.0]));
+        expected.insert(2, 100.0);
+        assert_eq!(eles(&trkseg), expected);
+
+        trkseg.splice(0, 3, vec![]);
+        expected.drain(..3);
+        assert_eq!(eles(&trkseg), expected);
+
+        let len = trkseg.len();
+        trkseg.splice(len, len, points(&[7.0, 8.0]));
+        expected.extend([7.0, 8.0]);
+        assert_eq!(eles(&trkseg), expected);
+
+        let len = trkseg.len();
+        trkseg.splice(0, len, vec![]);
+        assert_eq!(trkseg.len(), 0);
+        assert!(trkseg.first_index().is_none());
+    }
+
+    #[test]
+    fn test_splice_keeps_untouched_chunks_shared() {
+        let mut trkseg = create_track_segment(5);
+        let before = trkseg.chunks.clone();
+        // inside the third chunk only
+        trkseg.splice(4, 5, points(&[-1.0]));
+        assert!(Rc::ptr_eq(&trkseg.chunks[0], &before[0]));
+        assert!(Rc::ptr_eq(&trkseg.chunks[1], &before[1]));
+        assert!(Rc::ptr_eq(trkseg.chunks.last().unwrap(), &before[4]));
+        assert!(Rc::ptr_eq(
+            &trkseg.chunks[trkseg.chunks.len() - 2],
+            &before[3]
+        ));
+    }
+
+    #[test]
+    fn test_splice_append_extends_last_chunk_and_respects_max_size() {
+        let mut trkseg = TrackSegment::default();
+        for i in 0..10_000 {
+            let len = trkseg.len();
+            trkseg.splice(len, len, points(&[i as f64]));
+        }
+        assert_eq!(trkseg.len(), 10_000);
+        assert!(trkseg.chunks.len() <= 3);
+        assert!(trkseg.chunks.iter().all(|c| c.trkpt.len() <= 4096));
+        assert_eq!(trkseg[9_999].ele, 9_999.0);
+        assert_eq!(*trkseg.cumul_length.last().unwrap(), 10_000);
+    }
+
     #[test]
     fn test_len() {
         let nb_chunks = 10;
diff --git a/gpx-rs/engine/src/core/gpx/trackpoint.rs b/gpx-rs/engine/src/core/gpx/trackpoint.rs
index 32ee7a23a..f724df429 100644
--- a/gpx-rs/engine/src/core/gpx/trackpoint.rs
+++ b/gpx-rs/engine/src/core/gpx/trackpoint.rs
@@ -1,6 +1,6 @@
 use crate::LngLat;
 
-#[derive(Debug, Default)]
+#[derive(Debug, Default, Clone)]
 pub struct Trackpoint {
     pub coordinates: LngLat,
     pub ele: f64,
diff --git a/gpx-rs/engine/src/engine/command/tools/splice_trackpoints.rs b/gpx-rs/engine/src/engine/command/tools/splice_trackpoints.rs
index 18207a574..e45cdfc75 100644
--- a/gpx-rs/engine/src/engine/command/tools/splice_trackpoints.rs
+++ b/gpx-rs/engine/src/engine/command/tools/splice_trackpoints.rs
@@ -1,5 +1,13 @@
-use crate::{Apply, CommandError, State};
+use std::rc::Rc;
 
+use crate::{Apply, CommandError, File, FileId, LngLat, Selection, State, Trackpoint};
+
+/// Replaces the trackpoints `start..end` of the last track segment of the selection by the
+/// given ones (a pure insertion when `start == end`, a pure removal when there are no new
+/// points).
+///
+/// The selection can be made of several files, tracks or track segments: the indices are
+/// meant for its very last segment, in file order, then track order, then segment order.
 #[derive(Debug)]
 pub struct SpliceTrackpoints<'a> {
     pub start: u32,
@@ -10,8 +18,288 @@ pub struct SpliceTrackpoints<'a> {
 }
 
 impl Apply for SpliceTrackpoints<'_> {
-    fn apply(self, _state: &mut State) -> Result<(), CommandError> {
-        // TODO
-        Err(CommandError::NotImplemented("splice_trackpoints"))
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let (start, end) = (self.start as usize, self.end as usize);
+        if start > end || self.lng.len() != self.lat.len() || self.lat.len() != self.ele.len() {
+            return Err(CommandError::InvalidData(
+                "invalid trackpoints range".into(),
+            ));
+        }
+        let (file_id, trk, seg) = last_segment(state).ok_or(CommandError::NothingToDo)?;
+        let mut file = (*state.files[&file_id]).clone();
+        let segment = &mut file.trk[trk].trkseg[seg];
+        if end > segment.len() {
+            return Err(CommandError::InvalidData(
+                "trackpoints range out of bounds".into(),
+            ));
+        }
+        if start == end && self.lng.is_empty() {
+            return Err(CommandError::NothingToDo);
+        }
+        let points = (0..self.lng.len())
+            .map(|i| Trackpoint {
+                coordinates: LngLat {
+                    lng: self.lng[i],
+                    lat: self.lat[i],
+                },
+                ele: self.ele[i],
+                ..Default::default()
+            })
+            .collect();
+        segment.splice(start, end, points);
+        segment.rev_id = Default::default();
+        state.files.insert(file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+/// Position (file, track index, segment index) of the last segment of the selection.
+fn last_segment(state: &State) -> Option<(FileId, usize, usize)> {
+    let last_of_track = |file: &File, trk: usize| file.trk[trk].trkseg.len().checked_sub(1);
+    let last_of_file = |file: &File, filter: &dyn Fn(usize) -> bool| {
+        (0..file.trk.len())
+            .rev()
+            .filter(|&trk| filter(trk))
+            .find_map(|trk| last_of_track(file, trk).map(|seg| (trk, seg)))
+    };
+    match &*state.selection {
+        Selection::File { file_ids } => state
+            .order
+            .0
+            .iter()
+            .rev()
+            .filter(|id| file_ids.contains(id))
+            .find_map(|id| {
+                let (trk, seg) = last_of_file(state.files.get(id)?, &|_| true)?;
+                Some((*id, trk, seg))
+            }),
+        Selection::Track { file_id, trk_ids } => {
+            let file = state.files.get(file_id)?;
+            let (trk, seg) = last_of_file(file, &|trk| trk_ids.contains(&file.trk[trk].id))?;
+            Some((*file_id, trk, seg))
+        }
+        Selection::TrackSegment {
+            file_id,
+            trk_id,
+            trkseg_ids,
+        } => {
+            let file = state.files.get(file_id)?;
+            let trk = file.trk.iter().position(|trk| trk.id == *trk_id)?;
+            let seg = file.trk[trk]
+                .trkseg
+                .iter()
+                .rposition(|seg| trkseg_ids.contains(&seg.id))?;
+            Some((*file_id, trk, seg))
+        }
+        Selection::Empty | Selection::Waypoints { .. } | Selection::Waypoint { .. } => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let id = fx.order.0[0];
+        let trk = &fx.files[&id].trk[0];
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trk.trkseg[0].id]),
+        };
+        (fx, id)
+    }
+
+    fn splice<'a>(
+        start: u32,
+        end: u32,
+        lng: &'a [f64],
+        lat: &'a [f64],
+        ele: &'a [f64],
+    ) -> SpliceTrackpoints<'a> {
+        SpliceTrackpoints {
+            start,
+            end,
+            lng,
+            lat,
+            ele,
+        }
+    }
+
+    #[test]
+    fn test_splice_replaces_points_of_selected_segment_only() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let len = before.trk[0].trkseg[0].len();
+        assert!(len >= 3);
+
+        splice(1, 3, &[1.0, 2.0, 3.0], &[4.0, 5.0, 6.0], &[7.0, 8.0, 9.0])
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after = &fx.files[&id];
+        let (old, new) = (&before.trk[0].trkseg[0], &after.trk[0].trkseg[0]);
+        assert_eq!(new.len(), len + 1);
+        assert_eq!(new[0].coordinates.lng, old[0].coordinates.lng);
+        assert_eq!(new[1].coordinates.lng, 1.0);
+        assert_eq!(new[3].coordinates.lat, 6.0);
+        assert_eq!(new[3].ele, 9.0);
+        assert_eq!(new[4].coordinates.lng, old[3].coordinates.lng);
+        assert_ne!(new.rev_id, old.rev_id);
+        assert_eq!(new.id, old.id);
+        // other segments and tracks keep their revision
+        for (b, a) in before.trk.iter().zip(&after.trk) {
+            for (b, a) in b.trkseg.iter().zip(&a.trkseg) {
+                if a.id != new.id {
+                    assert_eq!(a.rev_id, b.rev_id);
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_splice_append_and_remove() {
+        let (mut fx, id) = loaded();
+        let len = fx.files[&id].trk[0].trkseg[0].len() as u32;
+        splice(len, len, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let seg = &fx.files[&id].trk[0].trkseg[0];
+        assert_eq!(seg.len(), len as usize + 1);
+        assert_eq!(seg[len as usize].ele, 3.0);
+
+        splice(0, len + 1, &[], &[], &[])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(fx.files[&id].trk[0].trkseg[0].len(), 0);
+    }
+
+    #[test]
+    fn test_splice_invalid_arguments_change_nothing() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let len = before.trk[0].trkseg[0].len() as u32;
+        let results = [
+            splice(2, 1, &[], &[], &[]).apply(&mut fx.state()),
+            splice(0, 0, &[1.0], &[], &[]).apply(&mut fx.state()),
+            splice(0, len + 1, &[], &[], &[]).apply(&mut fx.state()),
+        ];
+        assert!(
+            results
+                .iter()
+                .all(|r| matches!(r, Err(CommandError::InvalidData(_))))
+        );
+        assert_eq!(
+            splice(0, 0, &[], &[], &[]).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(std::rc::Rc::ptr_eq(&fx.files[&id], &before));
+    }
+
+    #[test]
+    fn test_splice_needs_a_segment_selection() {
+        let (mut fx, _) = loaded();
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            splice(0, 0, &[1.0], &[1.0], &[1.0]).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_splice_targets_last_segment_of_the_selection() {
+        let (mut fx, id) = loaded();
+        let file = fx.files[&id].clone();
+        assert!(file.trk.len() >= 2);
+        let last_trk = file.trk.len() - 1;
+        let last_seg = file.trk[last_trk].trkseg.len() - 1;
+
+        // whole file selected: last segment of its last track
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        splice(0, 0, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let after = &fx.files[&id];
+        for (t, (b, a)) in file.trk.iter().zip(&after.trk).enumerate() {
+            for (s, (b, a)) in b.trkseg.iter().zip(&a.trkseg).enumerate() {
+                let target = (t, s) == (last_trk, last_seg);
+                assert_eq!(a.len(), b.len() + usize::from(target));
+                assert_eq!(a.rev_id != b.rev_id, target);
+            }
+        }
+
+        // several tracks selected: last selected one (in file order, whatever the set order)
+        let ids: Vec<_> = file.trk.iter().map(|t| t.id).collect();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([ids[1], ids[0]]),
+        };
+        let len = |fx: &Fixture, t: usize| {
+            let trk = &fx.files[&id].trk[t];
+            trk.trkseg.last().unwrap().len()
+        };
+        let (l0, l1) = (len(&fx, 0), len(&fx, 1));
+        splice(0, 0, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(len(&fx, 0), l0);
+        assert_eq!(len(&fx, 1), l1 + 1);
+
+        // several segments selected
+        let trk = &fx.files[&id].trk[0];
+        let seg_ids: Vec<_> = trk.trkseg.iter().map(|s| s.id).collect();
+        if seg_ids.len() >= 2 {
+            fx.selection = Selection::TrackSegment {
+                file_id: id,
+                trk_id: trk.id,
+                trkseg_ids: seg_ids.iter().copied().collect(),
+            };
+            let lens: Vec<_> = trk.trkseg.iter().map(|s| s.len()).collect();
+            splice(0, 0, &[1.0], &[2.0], &[3.0])
+                .apply(&mut fx.state())
+                .unwrap();
+            let after: Vec<_> = fx.files[&id].trk[0]
+                .trkseg
+                .iter()
+                .map(|s| s.len())
+                .collect();
+            let n = lens.len();
+            assert_eq!(after[..n - 1], lens[..n - 1]);
+            assert_eq!(after[n - 1], lens[n - 1] + 1);
+        }
+    }
+
+    #[test]
+    fn test_splice_on_multiple_files_uses_last_in_file_order() {
+        let (mut fx, first) = loaded();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let second = fx.order.0[1];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([second, first]),
+        };
+        let total = |fx: &Fixture, id: FileId| -> usize {
+            fx.files[&id]
+                .trk
+                .iter()
+                .flat_map(|t| &t.trkseg)
+                .map(|s| s.len())
+                .sum()
+        };
+        let (a, b) = (total(&fx, first), total(&fx, second));
+        splice(0, 0, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(total(&fx, first), a);
+        assert_eq!(total(&fx, second), b + 1);
     }
 }