diff --git a/crates/engine/src/cmd/edit.rs b/crates/engine/src/cmd/edit.rs
index 45ed6950..f18010df 100644
--- a/crates/engine/src/cmd/edit.rs
+++ b/crates/engine/src/cmd/edit.rs
@@ -35,8 +35,13 @@ pub static COMMANDS: &[CommandSpec] = &[
         .params("feature: id|name → features deleted with it, and features that would fail without it"),
     CommandSpec::new("timeline.suppress", "Suppress Feature", suppress).params("feature: id|name, suppressed?: bool (default toggles)"),
     CommandSpec::new("timeline.edit", "Edit Feature", edit_feature).params(
-        "feature: id|name, set: {fields to change, e.g. {\"extent\": {\"distance\": \"30\"}}} → recomputed: features rebuilt, \
-             restored: features whose earlier result for the same inputs was reused",
+        "feature: id|name, set: {fields to change, merged into the feature's definition as timeline.inspect returns it, \
+         e.g. {\"extent\": {\"distance\": \"30\"}} (extrude), {\"angle\": \"90 deg\"} (revolve); \
+         expressions are text} → recomputed: features rebuilt, restored: features whose earlier result for the same inputs was reused",
+    ),
+    CommandSpec::new("timeline.inspect", "Inspect Feature", inspect_feature).noundo().params(
+        "feature: id|name → type, definition (the fields timeline.edit's set changes, with their current values), \
+         inputs: [{label, param, expression, unit}] (named inputs parameters.change can also set), error, warning",
     ),
     CommandSpec::new("select.set", "Select", select_set)
         .noundo()
@@ -190,6 +195,52 @@ fn merge(dst: &mut Value, src: &Value, depth: usize) {
     }
 }
 
+/// Fields of a stored feature left out of its definition: bookkeeping timeline.edit recomputes, and
+/// the name and suppression, which timeline.rename and timeline.suppress change.
+const NOT_EDITABLE: &[&str] = &["id", "type", "name", "suppressed", "param_names", "edge_refs", "edge_names", "face_names"];
+
+fn inspect_feature(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "timeline.inspect";
+    let id = feature_id(s, p.get("feature"), cmd)?;
+    let f = s.doc.feature(id).ok_or_else(|| bad(cmd, "feature"))?;
+    let mut def = serde_json::to_value(f).map_err(|e| EngineError::Other(e.to_string()))?;
+    let mut omitted = Vec::new();
+    if let Some(o) = def.as_object_mut() {
+        for k in NOT_EDITABLE {
+            o.remove(*k);
+        }
+        // Large payloads that timeline.edit cannot change.
+        let heavy: &[(&str, &str)] = match &f.kind {
+            FeatureKind::Sketch { .. } => &[("sketch", "the sketch geometry (sketch.inspect; edit it with the sketch commands)")],
+            FeatureKind::Import { .. } => &[("step", "the imported STEP text"), ("components", "the imported product tree")],
+            FeatureKind::MeshImport { .. } => &[("meshes", "the imported meshes")],
+            _ => &[],
+        };
+        for (k, why) in heavy {
+            if o.remove(*k).is_some() {
+                omitted.push(json!({"field": k, "what": why}));
+            }
+        }
+    }
+    let inputs: Vec<Value> = f
+        .kind
+        .inputs()
+        .into_iter()
+        .enumerate()
+        .map(|(i, (label, e, k))| {
+            json!({"label": label, "param": f.param_names.get(i).filter(|n| !n.is_empty()), "expression": e, "unit": k.default_unit()})
+        })
+        .collect();
+    let marker = s.doc.marker.unwrap_or(usize::MAX);
+    let rolled_back = s.doc.features.iter().position(|x| x.id == id).is_some_and(|i| i >= marker);
+    let r = s.model.result(id);
+    Ok(json!({
+        "id": f.id, "name": f.name, "type": f.kind.type_name(), "suppressed": f.suppressed, "rolled_back": rolled_back,
+        "definition": def, "omitted": omitted, "inputs": inputs,
+        "error": r.and_then(|r| r.error.clone()), "warning": r.and_then(|r| r.warning.clone()),
+    }))
+}
+
 fn edit_feature(s: &mut Session, p: &Value) -> Result<Value> {
     let cmd = "timeline.edit";
     let id = feature_id(s, p.get("feature"), cmd)?;
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index b16559dc..e087b067 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -419,6 +419,46 @@ fn sample_edges_chain_and_faces() {
     assert!(m.edge_faces.iter().all(|f| !f.is_empty()));
 }
 
+/// timeline.inspect returns a feature's definition in the shape timeline.edit's `set` takes, so
+/// an agent can read the field names instead of guessing them.
+#[test]
+fn timeline_inspect_shows_what_timeline_edit_changes() {
+    let mut s = Session::default();
+    run(&mut s, "sketch.create", json!({"plane": "XY", "name": "Base"}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [40, 30]}));
+    run(&mut s, "sketch.finish", json!({}));
+    run(&mut s, "solid.extrude", json!({"distance": 10, "name": "Slab"}));
+    run(&mut s, "solid.fillet", json!({"edges": [[20, 0, 10]], "radius": 2, "name": "Round"}));
+    let i = run(&mut s, "timeline.inspect", json!({"feature": "Slab"}));
+    assert_eq!(i["type"], "ExtrudeFeature", "{i}");
+    assert_eq!(i["definition"]["extent"]["distance"], "10", "{i}");
+    assert_eq!(i["definition"]["operation"], "new_body", "{i}");
+    assert!(i["definition"].get("type").is_none() && i["definition"].get("param_names").is_none(), "{i}");
+    assert_eq!(i["inputs"][0]["label"], "Distance", "{i}");
+    assert_eq!(i["inputs"][0]["unit"], "mm", "{i}");
+    let d = i["inputs"][0]["param"].as_str().unwrap().to_string();
+    // The definition's field names are what timeline.edit takes.
+    run(&mut s, "timeline.edit", json!({"feature": "Slab", "set": {"extent": {"distance": "12"}}}));
+    let i = run(&mut s, "timeline.inspect", json!({"feature": i["id"]}));
+    assert_eq!(i["definition"]["extent"]["distance"], "12", "{i}");
+    assert_eq!(i["inputs"][0]["param"], d.as_str(), "{i}");
+    let f = run(&mut s, "timeline.inspect", json!({"feature": "Round"}));
+    assert_eq!(f["definition"]["radius"], "2", "{f}");
+    run(&mut s, "timeline.edit", json!({"feature": "Round", "set": {"radius": "3"}}));
+    assert_eq!(run(&mut s, "timeline.inspect", json!({"feature": "Round"}))["definition"]["radius"], "3");
+    // A sketch leaves its geometry out (sketch.inspect has it) and says so.
+    let k = run(&mut s, "timeline.inspect", json!({"feature": "Base"}));
+    assert!(k["definition"].get("sketch").is_none() && k["definition"].get("plane").is_some(), "{k}");
+    assert_eq!(k["omitted"][0]["field"], "sketch", "{k}");
+    // Read-only: no undo step; bad input is refused.
+    let undo = s.undo.len();
+    run(&mut s, "timeline.inspect", json!({"feature": "Slab"}));
+    assert_eq!(s.undo.len(), undo);
+    for bad in [json!({}), json!({"feature": "Nope"}), json!({"feature": [1]}), json!({"feature": 1e300}), json!({"feature": null})] {
+        assert!(s.execute("timeline.inspect", &bad).is_err(), "{bad}");
+    }
+}
+
 #[test]
 fn timeline_edits_reresolve_references() {
     let mut s = Session::default();
diff --git a/docs/book/src/guide/features.md b/docs/book/src/guide/features.md
index 9aeff456..16124695 100644
--- a/docs/book/src/guide/features.md
+++ b/docs/book/src/guide/features.md
@@ -52,6 +52,45 @@ Feature references to faces and edges are stored by name, so an upstream edit th
 keeps them on the right face (see [Persistent naming](../dev/naming.md)). When a reference can't
 be found, the feature warns instead of silently picking another face.
 
+## Editing a feature from a script
+
+`timeline.inspect {feature}` returns a feature's `definition`: the fields `timeline.edit` changes,
+with their current values. `timeline.edit {feature, set}` merges `set` into that definition
+(objects are merged field by field, anything else replaces the value), rebuilds the feature and
+reports `recomputed` and `restored`. The feature's type cannot change, and sketch geometry is
+edited with the sketch commands. Expressions are text (`"30"`, `"30 mm"`, `"width / 2"`,
+`"45 deg"`); a bare number is a length in the design's units, or degrees for an angle.
+
+```json
+{"command": "timeline.inspect", "params": {"feature": "Slab"}}
+→ {"type": "ExtrudeFeature",
+   "definition": {"sketch": 1, "profiles": {"type": "all"}, "operation": "new_body",
+                  "extent": {"distance": "10", "direction": "positive"}},
+   "inputs": [{"label": "Distance", "param": "d1", "expression": "10", "unit": "mm"}], …}
+{"command": "timeline.edit", "params": {"feature": "Slab", "set": {"extent": {"distance": "12"}}}}
+```
+
+`inputs` lists the feature's named inputs. `parameters.change {name: "d1", expression}` sets one
+of those directly. Optional fields that are not set do not appear in the definition; they can
+still be added through `set`. The fields of the common features:
+
+| Feature | Fields |
+|---|---|
+| Extrude | `extent`: {`distance`, `direction`: positive\|negative\|symmetric, `distance2`, `start_offset`, `through_all`, `taper`, `to`, `to_offset`, `from`}; `operation`: new_body\|join\|cut\|intersect; `targets`; `profiles`; `sketch` |
+| Revolve | `angle`, `angle2`, `symmetric`, `axis`, `to`, `operation`, `targets`, `profiles`, `sketch` |
+| Fillet | `radius`, `edges` (a point on each edge), `body`, `style` |
+| Chamfer | `distance`, `distance2` or `angle`, `flip`, `edges`, `body` |
+| Box | `length`, `width`, `height`, `corner`, `operation` |
+| Cylinder | `radius`, `height`, `base`, `axis`, `operation` |
+| Hole | `diameter`, `depth`, `position`, `direction`, `hole` (simple, drilled, counterbore, countersink), `thread`, `to` |
+| Shell | `thickness`, `faces`, `direction`, `body`, `tangent_chain` |
+| Draft | `angle`, `faces`, `neutral`, `pull`, `body` |
+| Offset face | `distance`, `faces`, `body` |
+| Pattern | `pattern` (its kind and counts/spacing), `features`, `bodies` |
+| Mirror | `plane`, `features`, `bodies`, `combine` |
+
+For any other feature, `timeline.inspect` shows the fields.
+
 Press **Delete** on anything selected (bodies, faces, sketches, features, planes, components,
 canvases). It runs as one undoable step and lists the features that would go with it or fail.
 
diff --git a/docs/mcp.md b/docs/mcp.md
index 63370d71..d8bb0c49 100644
--- a/docs/mcp.md
+++ b/docs/mcp.md
@@ -62,6 +62,11 @@ Claude Desktop (`claude_desktop_config.json`), bridged to a running app:
 | `open` | `path` | Open a `.solvecraft` design, a STEP file (`.step`/`.stp`) as a new design holding its bodies (an Import base feature), or a 3MF/STL file as mesh bodies. |
 | `save` | `path?` | Save the design (to its current file without `path`). |
 
+To change a feature after it is made, read its definition with `execute` `timeline.inspect`
+(`{feature}`: id or name) and change fields with `timeline.edit` (`{feature, set}`; e.g.
+`{"extent": {"distance": "30"}}`). The fields per feature type are listed in the book's
+*Solid features* chapter.
+
 Resources: `solvecraft://design` (inspect JSON with measurements) and `solvecraft://commands`
 (the catalog).