diff --git a/crates/doc/src/dimension.rs b/crates/doc/src/dimension.rs
index 81713baf1..5ca27311e 100644
--- a/crates/doc/src/dimension.rs
+++ b/crates/doc/src/dimension.rs
@@ -123,7 +123,7 @@ pub enum TextAlignment {
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
-#[serde(default, rename_all = "camelCase", deny_unknown_fields)]
+#[serde(default, rename_all = "camelCase")]
 pub struct DimensionOptions {
     pub units: LengthUnit,
     pub precision: usize,
@@ -182,6 +182,18 @@ impl Default for DimensionOptions {
 }
 
 impl DimensionOptions {
+    /// Options given to a command or a tool: unknown keys are refused there, while files load
+    /// tolerantly so a newer version's options don't stop a document opening.
+    pub fn from_params(v: serde_json::Value) -> Result<Self, String> {
+        if let (Some(given), Ok(serde_json::Value::Object(known))) = (v.as_object(), serde_json::to_value(Self::default()))
+            && let Some(k) = given.keys().find(|k| !known.contains_key(*k))
+        {
+            return Err(format!("Unknown dimension option {k}"));
+        }
+        let o: Self = serde_json::from_value(v).map_err(|e| e.to_string())?;
+        o.validate()?;
+        Ok(o)
+    }
     pub fn factor(&self) -> Result<f64, String> {
         let (a, b) = self.scale.split_once(':').ok_or("Scale must be drawing:real, for example 1:10")?;
         let parse = |s: &str| s.trim().parse::<f64>().ok().filter(|n| n.is_finite() && *n > 0.0 && *n <= 1e9);
@@ -236,7 +248,7 @@ impl DimensionOptions {
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
-#[serde(rename_all = "camelCase", deny_unknown_fields)]
+#[serde(rename_all = "camelCase")]
 pub struct SegmentRef {
     pub node: NodeId,
     pub subpath: usize,
@@ -263,7 +275,7 @@ impl SegmentRef {
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
-#[serde(tag = "kind", rename_all = "camelCase", deny_unknown_fields)]
+#[serde(tag = "kind", rename_all = "camelCase")]
 pub enum DimensionSource {
     Segment {
         edge: SegmentRef,
@@ -312,7 +324,7 @@ impl DimensionSource {
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
-#[serde(rename_all = "camelCase", deny_unknown_fields)]
+#[serde(rename_all = "camelCase")]
 pub struct PointRef {
     pub node: NodeId,
     pub subpath: usize,
@@ -326,7 +338,7 @@ impl PointRef {
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
-#[serde(rename_all = "camelCase", deny_unknown_fields)]
+#[serde(rename_all = "camelCase")]
 pub struct Dimension {
     pub mode: DimensionMode,
     pub a: Point,
diff --git a/crates/engine/src/cmd/dimension.rs b/crates/engine/src/cmd/dimension.rs
index 2e3ffae73..efc3e5fc7 100644
--- a/crates/engine/src/cmd/dimension.rs
+++ b/crates/engine/src/cmd/dimension.rs
@@ -46,9 +46,7 @@ fn error(s: impl ToString) -> EngineError {
 fn options(s: &Session, p: &Value) -> Result<DimensionOptions> {
     let default = s.tool_options_of("dimension");
     let value = p.get("options").cloned().unwrap_or_else(|| default.get("style").cloned().unwrap_or(json!({})));
-    let o: DimensionOptions = serde_json::from_value(value).map_err(error)?;
-    o.validate().map_err(error)?;
-    Ok(o)
+    DimensionOptions::from_params(value).map_err(error)
 }
 
 fn point(p: &Value, key: &str) -> Result<Point> {
diff --git a/crates/engine/src/tooling.rs b/crates/engine/src/tooling.rs
index fc0ef5586..a2cf5c956 100644
--- a/crates/engine/src/tooling.rs
+++ b/crates/engine/src/tooling.rs
@@ -455,8 +455,7 @@ impl Session {
         }
         if tool.unwrap_or(self.tool_id()) == "dimension" {
             if let Some(style) = values.get("style") {
-                let options: vectorcraft_doc::dimension::DimensionOptions = serde_json::from_value(style.clone()).map_err(|e| e.to_string())?;
-                options.validate()?;
+                vectorcraft_doc::dimension::DimensionOptions::from_params(style.clone())?;
             }
             if let Some(mode) = values.get("mode")
                 && !mode.as_str().is_some_and(|m| ["linear", "angular", "radial", "radius", "diameter"].contains(&m))
diff --git a/crates/engine/tests/dimensions.rs b/crates/engine/tests/dimensions.rs
index 9826bd2af..f65a292c7 100644
--- a/crates/engine/tests/dimensions.rs
+++ b/crates/engine/tests/dimensions.rs
@@ -357,3 +357,35 @@ fn dimension_cannot_measure_its_own_generated_art() {
     let child = s.doc().unwrap().doc.node(NodeId(id)).unwrap().children().unwrap()[0].id;
     assert!(s.execute("dimension.create", &json!({"source":{"kind":"segment","edge":{"node":child,"subpath":0,"segment":0}}})).is_err());
 }
+
+#[test]
+fn unknown_dimension_options_are_refused_by_commands_but_a_newer_file_still_opens() {
+    let mut s = session();
+    let line = edge(&mut s);
+    let source = json!({"kind":"segment","edge":{"node":line,"subpath":0,"segment":0}});
+    let bad = s.execute("dimension.create", &json!({"source":source,"options":{"units":"in","color":"red"}}));
+    assert!(bad.unwrap_err().to_string().contains("Unknown dimension option color"));
+    assert!(s.set_tool_option_cmd(&json!({"tool":"dimension","values":{"style":{"precison":2}}})).is_err());
+    let id = dim(&mut s, line);
+    let saved = vectorcraft_format::save(&s.doc().unwrap().doc, false);
+    let mut v: Value = serde_json::from_slice(&saved).unwrap();
+    // A later version's dimension carries fields this one doesn't know.
+    fn add_unknown(v: &mut Value) {
+        match v {
+            Value::Object(m) => {
+                if let Some(Value::Object(d)) = m.get_mut("dimension") {
+                    d.insert("later".into(), json!(1));
+                    if let Some(Value::Object(o)) = d.get_mut("options") {
+                        o.insert("later".into(), json!(true));
+                    }
+                }
+                m.values_mut().for_each(add_unknown);
+            }
+            Value::Array(a) => a.iter_mut().for_each(add_unknown),
+            _ => {}
+        }
+    }
+    add_unknown(&mut v);
+    let doc = vectorcraft_format::load(&serde_json::to_vec(&v).unwrap()).unwrap();
+    assert!(doc.node(NodeId(id)).unwrap().extras().dimension.is_some());
+}
diff --git a/crates/ui-egui/src/i18n/cs.tsv b/crates/ui-egui/src/i18n/cs.tsv
index 570f3778b..5a223e467 100644
--- a/crates/ui-egui/src/i18n/cs.tsv
+++ b/crates/ui-egui/src/i18n/cs.tsv
@@ -4851,6 +4851,7 @@ mark-style	Japanese	Japonské
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Poměr měřítka musí být mezi 1:1000000 a 1000000:1
 @msg	Second measured segment no longer exists	Druhý měřený segment už neexistuje
 @msg	Unknown dimension mode	Neznámý režim kóty
+@msg	Unknown dimension option {k}	Neznámá volba kóty {k}
 @msg	Unknown dimension style	Neznámý styl kóty
 @msg	Unknown unit	Neznámá jednotka
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/de.tsv b/crates/ui-egui/src/i18n/de.tsv
index def112ce7..597e7056f 100644
--- a/crates/ui-egui/src/i18n/de.tsv
+++ b/crates/ui-egui/src/i18n/de.tsv
@@ -4380,6 +4380,7 @@ theme	Appearance	Erscheinungsbild
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Das Maßstabsverhältnis muss zwischen 1:1000000 und 1000000:1 liegen
 @msg	Second measured segment no longer exists	Das zweite gemessene Segment existiert nicht mehr
 @msg	Unknown dimension mode	Unbekannter Bemaßungsmodus
+@msg	Unknown dimension option {k}	Unbekannte Bemaßungsoption {k}
 @msg	Unknown dimension style	Unbekannter Bemaßungsstil
 @msg	Unknown unit	Unbekannte Einheit
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/es.tsv b/crates/ui-egui/src/i18n/es.tsv
index dd32182cf..8538bbf99 100644
--- a/crates/ui-egui/src/i18n/es.tsv
+++ b/crates/ui-egui/src/i18n/es.tsv
@@ -4792,6 +4792,7 @@ mark-style	Japanese	Japonesas
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	La relación de escala debe estar entre 1:1000000 y 1000000:1
 @msg	Second measured segment no longer exists	El segundo segmento medido ya no existe
 @msg	Unknown dimension mode	Modo de cota desconocido
+@msg	Unknown dimension option {k}	Opción de cota desconocida {k}
 @msg	Unknown dimension style	Estilo de cota desconocido
 @msg	Unknown unit	Unidad desconocida
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/fr.tsv b/crates/ui-egui/src/i18n/fr.tsv
index 7917f1950..2eb9d59ab 100644
--- a/crates/ui-egui/src/i18n/fr.tsv
+++ b/crates/ui-egui/src/i18n/fr.tsv
@@ -4850,6 +4850,7 @@ theme	Appearance	Apparence
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Le rapport d’échelle doit être compris entre 1:1000000 et 1000000:1
 @msg	Second measured segment no longer exists	Le second segment mesuré n’existe plus
 @msg	Unknown dimension mode	Mode de cote inconnu
+@msg	Unknown dimension option {k}	Option de cote inconnue {k}
 @msg	Unknown dimension style	Style de cote inconnu
 @msg	Unknown unit	Unité inconnue
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/hu.tsv b/crates/ui-egui/src/i18n/hu.tsv
index 184fa5c55..26655c258 100644
--- a/crates/ui-egui/src/i18n/hu.tsv
+++ b/crates/ui-egui/src/i18n/hu.tsv
@@ -4817,6 +4817,7 @@ imageTrace	Outline	Körvonal
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	A lépték aránya 1:1000000 és 1000000:1 között lehet
 @msg	Second measured segment no longer exists	A második mért szakasz már nem létezik
 @msg	Unknown dimension mode	Ismeretlen méretezési mód
+@msg	Unknown dimension option {k}	Ismeretlen méretezési beállítás: {k}
 @msg	Unknown dimension style	Ismeretlen méretezési stílus
 @msg	Unknown unit	Ismeretlen mértékegység
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/it.tsv b/crates/ui-egui/src/i18n/it.tsv
index 9cd975ed5..674ebb6ae 100644
--- a/crates/ui-egui/src/i18n/it.tsv
+++ b/crates/ui-egui/src/i18n/it.tsv
@@ -4425,6 +4425,7 @@ lighting	Light	Luce
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Il rapporto di scala deve essere compreso tra 1:1000000 e 1000000:1
 @msg	Second measured segment no longer exists	Il secondo segmento misurato non esiste più
 @msg	Unknown dimension mode	Modalità di quota sconosciuta
+@msg	Unknown dimension option {k}	Opzione di quota sconosciuta {k}
 @msg	Unknown dimension style	Stile di quota sconosciuto
 @msg	Unknown unit	Unità sconosciuta
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/ja.tsv b/crates/ui-egui/src/i18n/ja.tsv
index 0b6d27759..aea1c8059 100644
--- a/crates/ui-egui/src/i18n/ja.tsv
+++ b/crates/ui-egui/src/i18n/ja.tsv
@@ -4420,6 +4420,7 @@ lighting	Light	ライト
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	縮尺の比率は 1:1000000 から 1000000:1 の間にしてください
 @msg	Second measured segment no longer exists	2 番目の測定セグメントはもう存在しません
 @msg	Unknown dimension mode	寸法のモードが不明です
+@msg	Unknown dimension option {k}	不明な寸法オプション {k}
 @msg	Unknown dimension style	寸法のスタイルが不明です
 @msg	Unknown unit	単位が不明です
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/ko.tsv b/crates/ui-egui/src/i18n/ko.tsv
index 229be3ef0..0365abac3 100644
--- a/crates/ui-egui/src/i18n/ko.tsv
+++ b/crates/ui-egui/src/i18n/ko.tsv
@@ -4389,6 +4389,7 @@ lighting	Light	광원
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	축척 비율은 1:1000000에서 1000000:1 사이여야 합니다
 @msg	Second measured segment no longer exists	두 번째 측정 세그먼트가 더 이상 없습니다
 @msg	Unknown dimension mode	알 수 없는 치수 모드
+@msg	Unknown dimension option {k}	알 수 없는 치수 옵션 {k}
 @msg	Unknown dimension style	알 수 없는 치수 스타일
 @msg	Unknown unit	알 수 없는 단위
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/pl.tsv b/crates/ui-egui/src/i18n/pl.tsv
index ce9e2b268..98e0c3a15 100644
--- a/crates/ui-egui/src/i18n/pl.tsv
+++ b/crates/ui-egui/src/i18n/pl.tsv
@@ -4692,6 +4692,7 @@ mark-style	Japanese	Japońskie
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Współczynnik skali musi mieścić się między 1:1000000 a 1000000:1
 @msg	Second measured segment no longer exists	Drugi mierzony odcinek już nie istnieje
 @msg	Unknown dimension mode	Nieznany tryb wymiaru
+@msg	Unknown dimension option {k}	Nieznana opcja wymiaru {k}
 @msg	Unknown dimension style	Nieznany styl wymiaru
 @msg	Unknown unit	Nieznana jednostka
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/ru.tsv b/crates/ui-egui/src/i18n/ru.tsv
index 7a75c4bce..0eb092e65 100644
--- a/crates/ui-egui/src/i18n/ru.tsv
+++ b/crates/ui-egui/src/i18n/ru.tsv
@@ -4421,6 +4421,7 @@ lighting	Light	Свет
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Соотношение масштаба должно быть от 1:1000000 до 1000000:1
 @msg	Second measured segment no longer exists	Второй измеряемый сегмент больше не существует
 @msg	Unknown dimension mode	Неизвестный режим размера
+@msg	Unknown dimension option {k}	Неизвестный параметр размера {k}
 @msg	Unknown dimension style	Неизвестный стиль размера
 @msg	Unknown unit	Неизвестная единица
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/uk.tsv b/crates/ui-egui/src/i18n/uk.tsv
index 47ea60f9c..5d5902e11 100644
--- a/crates/ui-egui/src/i18n/uk.tsv
+++ b/crates/ui-egui/src/i18n/uk.tsv
@@ -4405,6 +4405,7 @@ lighting	Light	Світло
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Співвідношення масштабу має бути від 1:1000000 до 1000000:1
 @msg	Second measured segment no longer exists	Другий виміряний сегмент більше не існує
 @msg	Unknown dimension mode	Невідомий режим розміру
+@msg	Unknown dimension option {k}	Невідомий параметр розміру {k}
 @msg	Unknown dimension style	Невідомий стиль розміру
 @msg	Unknown unit	Невідома одиниця
 # Revolve cap description
diff --git a/crates/ui-egui/src/i18n/vi.tsv b/crates/ui-egui/src/i18n/vi.tsv
index dbf15afd9..9d0dd9292 100644
--- a/crates/ui-egui/src/i18n/vi.tsv
+++ b/crates/ui-egui/src/i18n/vi.tsv
@@ -4404,6 +4404,7 @@ theme	Appearance	Giao diện
 @msg	Scale ratio must be between 1:1000000 and 1000000:1	Tỷ lệ phải nằm trong khoảng 1:1000000 đến 1000000:1
 @msg	Second measured segment no longer exists	Đoạn được đo thứ hai không còn tồn tại
 @msg	Unknown dimension mode	Chế độ kích thước không xác định
+@msg	Unknown dimension option {k}	Tùy chọn kích thước không xác định {k}
 @msg	Unknown dimension style	Kiểu kích thước không xác định
 @msg	Unknown unit	Đơn vị không xác định
 # Revolve cap description