diff --git a/.changepacks/changepack_log_theme_variable_clashes.json b/.changepacks/changepack_log_theme_variable_clashes.json
new file mode 100644
index 000000000..50dddbfd3
--- /dev/null
+++ b/.changepacks/changepack_log_theme_variable_clashes.json
@@ -0,0 +1,8 @@
+{
+  "changes": {
+    "bindings/devup-ui-wasm/package.json": "Patch",
+    "bindings/devup-ui-binding/package.json": "Patch"
+  },
+  "note": "Theme tokens of different kinds can no longer silently share a CSS variable: a color `card` and a shadow `card` both declared `--card`, so one replaced the other in `:root`. New build error: `theme: color token 'card' and shadow token 'card' both become the CSS variable --card: rename one`, raised when the theme is registered for any two of colors, `length` and `shadow` (names compared after dots become dashes, so `gray.100` and `gray-100` clash too)",
+  "date": "2026-11-15T00:00:00.000Z"
+}
diff --git a/apps/landing/src/app/(detail)/docs/devup/colors/page.mdx b/apps/landing/src/app/(detail)/docs/devup/colors/page.mdx
index f62a0709a..69b421f58 100644
--- a/apps/landing/src/app/(detail)/docs/devup/colors/page.mdx
+++ b/apps/landing/src/app/(detail)/docs/devup/colors/page.mdx
@@ -116,7 +116,7 @@ Each variant also sets the page's native color scheme — form controls, scrollb
 }
 ```
 
-Token names start with a letter, a digit or `_` and continue with letters, digits, `-`, `_` and `.` (`primary`, `text-primary`, `gray.100`); a dot becomes a dash in the CSS variable, so `gray.100` is `var(--gray-100)`. The build reports a name outside these characters, and two tokens of a variant that become the same variable (`a-b` and `a.b`), instead of emitting CSS the browser would drop.
+Token names start with a letter, a digit or `_` and continue with letters, digits, `-`, `_` and `.` (`primary`, `text-primary`, `gray.100`); a dot becomes a dash in the CSS variable, so `gray.100` is `var(--gray-100)`. The build reports a name outside these characters, and two tokens of a variant that become the same variable (`a-b` and `a.b`), instead of emitting CSS the browser would drop. Colors, `length` and `shadow` tokens share one namespace of CSS variables, so a color `card` and a shadow `card` (both `--card`) are a build error too: rename one.
 
 ## Semantic Color Naming
 
diff --git a/libs/sheet/src/atom_identity_tests/first_value.rs b/libs/sheet/src/atom_identity_tests/first_value.rs
index fb0fb592e..981206cfc 100644
--- a/libs/sheet/src/atom_identity_tests/first_value.rs
+++ b/libs/sheet/src/atom_identity_tests/first_value.rs
@@ -3,7 +3,7 @@ use super::*;
 fn token_theme(first: &str) -> Theme {
     serde_json::from_value(serde_json::json!({
         "length": {"default": {"space": [first, "2px"], "zero": ["0px", "4px"], "nullable": [null, "3px", "4px"]}},
-        "shadows": {"default": {"card": ["0 1px 2px black", "0 2px 4px black"], "space": ["0 3px 4px black", "0 4px 8px black"]}}
+        "shadows": {"default": {"card": ["0 1px 2px black", "0 2px 4px black"], "lift": ["0 3px 4px black", "0 4px 8px black"]}}
     }))
     .unwrap_or_else(|error| panic!("{error}"))
 }
@@ -28,7 +28,7 @@ fn first_value_refs_resolve_without_aliasing_responsive_variables() {
     // Given
     let source = r#"import {Box} from '@devup-ui/react'; export const A=<>
       <Box w="$space"/><Box w={["$space"]}/><Box boxShadow={["$card"]}/>
-      <Box boxShadow={["$space"]}/><Box w="0px"/><Box w={["$zero"]}/>
+      <Box boxShadow={["$lift"]}/><Box w="0px"/><Box w={["$zero"]}/>
       <Box w={["$missing"]}/><Box w={["$nullable"]}/></>;"#;
     for atom in [false, true] {
         let mut sheet = token_sheet(atom);
diff --git a/libs/sheet/src/theme.rs b/libs/sheet/src/theme.rs
index 6f50afebb..c558b4bfa 100644
--- a/libs/sheet/src/theme.rs
+++ b/libs/sheet/src/theme.rs
@@ -624,8 +624,10 @@ impl ColorScheme {
     }
 }
 
+/// The theme of `devup.json`. Deserializing it checks the tokens of every
+/// kind together, as the derived field-by-field reading cannot
 #[derive(Serialize, Deserialize, Debug)]
-#[serde(rename_all = "camelCase")]
+#[serde(rename_all = "camelCase", remote = "Self")]
 pub struct Theme {
     #[serde(default, deserialize_with = "deserialize_color_themes")]
     pub colors: BTreeMap<String, ColorTheme>,
@@ -651,6 +653,58 @@ pub struct Theme {
     pub tailwind_css: String,
 }
 
+impl Serialize for Theme {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        Theme::serialize(self, serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for Theme {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        let theme = Theme::deserialize(deserializer)?;
+        check_token_kinds(&theme).map_err(serde::de::Error::custom)?;
+        Ok(theme)
+    }
+}
+
+/// Check that no two tokens of different kinds become one CSS variable, as a
+/// color `card` and a shadow `card` would both set `--card`. Tokens of one
+/// kind are checked as they are read; the same name in two variants of one
+/// kind is the same variable on purpose.
+fn check_token_kinds(theme: &Theme) -> Result<(), String> {
+    let colors = theme.colors.values().flat_map(|variant| {
+        variant
+            .entries
+            .values()
+            .map(|entry| ("color", entry.interface_key.as_str(), entry.css_key.clone()))
+    });
+    let mut seen: BTreeMap<String, (&str, &str)> = BTreeMap::new();
+    for (kind, name, css_key) in colors
+        .chain(token_variables("length", &theme.length))
+        .chain(token_variables("shadow", &theme.shadows))
+    {
+        let (other_kind, other) = *seen.entry(css_key.clone()).or_insert((kind, name));
+        if other_kind != kind {
+            return Err(format!(
+                "theme: {other_kind} token '{other}' and {kind} token '{name}' both become the CSS variable --{css_key}: rename one"
+            ));
+        }
+    }
+    Ok(())
+}
+
+/// The kind, name and CSS variable of each token of every variant of `themes`
+fn token_variables<'t>(
+    kind: &'static str,
+    themes: &'t BTreeMap<String, BTreeMap<String, TokenValues>>,
+) -> impl Iterator<Item = (&'static str, &'t str, String)> + 't {
+    themes.values().flat_map(move |variant| {
+        variant
+            .keys()
+            .map(move |name| (kind, name.as_str(), css_key_from(name).into_owned()))
+    })
+}
+
 /// Deserialize the color variants, naming the variant a token error is in
 fn deserialize_color_themes<'de, D>(
     deserializer: D,
@@ -2734,6 +2788,42 @@ mod tests {
         }
     }
 
+    // A color `card` and a shadow `card` both set `--card`, so one would
+    // silently replace the other
+    #[rstest::rstest]
+    #[case(
+        r##"{"colors":{"default":{"card":"#111"}},"shadow":{"default":{"card":"0 1px #000"}}}"##,
+        "theme: color token 'card' and shadow token 'card' both become the CSS variable --card: rename one"
+    )]
+    #[case(
+        r##"{"colors":{"default":{"a":"#111"},"dark":{"gray":{"100":"#222"}}},"length":{"default":{"gray-100":"4px"}}}"##,
+        "theme: color token 'gray.100' and length token 'gray-100' both become the CSS variable --gray-100: rename one"
+    )]
+    #[case(
+        r#"{"length":{"default":{"gap":"4px"}},"shadow":{"sm":{"x":"0 1px #000"},"lg":{"gap.y":"0 1px #000","gap":"0 2px #000"}}}"#,
+        "theme: length token 'gap' and shadow token 'gap' both become the CSS variable --gap: rename one"
+    )]
+    fn test_tokens_of_different_kinds_cannot_share_a_variable(
+        #[case] json: &str,
+        #[case] error: &str,
+    ) {
+        assert!(
+            theme_error(json).starts_with(error),
+            "{}",
+            theme_error(json)
+        );
+    }
+
+    #[test]
+    fn test_one_token_in_variants_of_its_kind_shares_a_variable() {
+        let theme: Theme = serde_json::from_str(
+            r##"{"colors":{"default":{"card":"#111"},"dark":{"card":"#eee"}},"length":{"default":{"gap":"4px"},"wide":{"gap":"8px"}}}"##,
+        )
+        .unwrap();
+        let json = serde_json::to_string(&theme).unwrap();
+        assert!(json.contains("\"length\""), "{json}");
+    }
+
     #[test]
     fn test_dotted_length_and_shadow_names_become_dashed_variables() {
         assert_eq!(