diff --git a/crates/tinymist-query/src/analysis/code_action.rs b/crates/tinymist-query/src/analysis/code_action.rs
index e59b6cf3..951b3854 100644
--- a/crates/tinymist-query/src/analysis/code_action.rs
+++ b/crates/tinymist-query/src/analysis/code_action.rs
@@ -99,7 +99,16 @@ impl<'a> CodeActionWorker<'a> {
     ) -> Option<()> {
         let cursor = (range.start + 1).min(self.source.text().len());
         let node = root.leaf_at_compat(cursor)?;
+        self.create_missing_variable(root, &node);
+        self.add_spaces_to_math_unknown_variable(&node);
+        Some(())
+    }
 
+    fn create_missing_variable(
+        &mut self,
+        root: &LinkedNode<'_>,
+        node: &LinkedNode<'_>,
+    ) -> Option<()> {
         let ident = 'determine_ident: {
             if let Some(ident) = node.cast::<ast::Ident>() {
                 break 'determine_ident ident.get().clone();
@@ -117,7 +126,7 @@ impl<'a> CodeActionWorker<'a> {
             Bad,
         }
 
-        let previous_decl = previous_items(node, |item| {
+        let previous_decl = previous_items(node.clone(), |item| {
             match item {
                 PreviousItem::Parent(parent, ..) => match parent.kind() {
                     SyntaxKind::LetBinding => {
@@ -198,6 +207,34 @@ impl<'a> CodeActionWorker<'a> {
         Some(())
     }
 
+    /// Add spaces between letters in an unknown math identifier: `$xyz$` -> `$x y z$`.
+    fn add_spaces_to_math_unknown_variable(&mut self, node: &LinkedNode<'_>) -> Option<()> {
+        let ident = node.cast::<ast::MathIdent>()?.get();
+
+        // Rewrite `a_ij` as `a_(i j)`, not `a_i j`.
+        // Likewise rewrite `ab/c` as `(a b)/c`, not `a b/c`.
+        let needs_parens = matches!(
+            node.parent_kind(),
+            Some(SyntaxKind::MathAttach | SyntaxKind::MathFrac)
+        );
+        let new_text = if needs_parens {
+            eco_format!("({})", ident.chars().join(" "))
+        } else {
+            ident.chars().join(" ").into()
+        };
+
+        let range = self.ctx.to_lsp_range(node.range(), &self.source);
+        let edit = self.local_edit(EcoSnippetTextEdit::new(range, new_text))?;
+        let action = CodeAction {
+            title: "Add spaces between letters".to_string(),
+            kind: Some(CodeActionKind::QUICKFIX),
+            edit: Some(edit),
+            ..CodeAction::default()
+        };
+        self.actions.push(action);
+        Some(())
+    }
+
     /// Automatically fixes file not found errors.
     pub fn autofix_file_not_found(
         &mut self,
diff --git a/crates/tinymist-query/src/check.rs b/crates/tinymist-query/src/check.rs
index c8d90180..58155f4e 100644
--- a/crates/tinymist-query/src/check.rs
+++ b/crates/tinymist-query/src/check.rs
@@ -14,6 +14,6 @@ impl SemanticRequest for CheckRequest {
 
     fn request(self, ctx: &mut LocalContext) -> Option<Self::Response> {
         let worker = DiagWorker::new(ctx);
-        Some(worker.check().convert_all(self.snap.diagnostics()))
+        Some(worker.full_check().convert_all(self.snap.diagnostics()))
     }
 }
diff --git a/crates/tinymist-query/src/code_action.rs b/crates/tinymist-query/src/code_action.rs
index c5a93cbd..568175bd 100644
--- a/crates/tinymist-query/src/code_action.rs
+++ b/crates/tinymist-query/src/code_action.rs
@@ -93,18 +93,22 @@ impl SemanticRequest for CodeActionRequest {
 
 #[cfg(test)]
 mod tests {
+    use typst::{diag::Warned, layout::PagedDocument};
+
     use super::*;
-    use crate::tests::*;
+    use crate::{DiagWorker, tests::*};
 
     #[test]
     fn test() {
         snapshot_testing("code_action", &|ctx, path| {
             let source = ctx.source_by_path(&path).unwrap();
 
+            let request_range = find_test_range(&source);
+            let code_action_ctx = compute_code_action_context(ctx, &source, &request_range);
             let request = CodeActionRequest {
                 path: path.clone(),
-                range: find_test_range(&source),
-                context: CodeActionContext::default(),
+                range: request_range,
+                context: code_action_ctx,
             };
 
             let result = request.request(ctx);
@@ -116,4 +120,37 @@ mod tests {
             })
         });
     }
+
+    fn compute_code_action_context(
+        ctx: &mut LocalContext,
+        source: &Source,
+        request_range: &LspRange,
+    ) -> CodeActionContext {
+        let Warned { output, warnings } = typst::compile::<PagedDocument>(&ctx.world);
+        let errors = output.err().unwrap_or_default();
+        let compiler_diagnostics = warnings.iter().chain(errors.iter());
+
+        // Run the linter for additional diagnostics as well.
+        let diagnostics = DiagWorker::new(ctx)
+            .check(source)
+            .convert_all(compiler_diagnostics)
+            .into_values()
+            .flatten();
+
+        CodeActionContext {
+            // The filtering here matches the LSP specification and VS Code behavior;
+            // see https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#codeActionContext:
+            //   `diagnostics`: An array of diagnostics known on the client side overlapping the range
+            //   provided to the textDocument/codeAction request [...]
+            diagnostics: diagnostics
+                .filter(|diag| ranges_overlap(&diag.range, request_range))
+                .collect(),
+            only: None,
+            trigger_kind: None,
+        }
+    }
+
+    fn ranges_overlap(r1: &LspRange, r2: &LspRange) -> bool {
+        !(r1.end <= r2.start || r2.end <= r1.start)
+    }
 }
diff --git a/crates/tinymist-query/src/diagnostics.rs b/crates/tinymist-query/src/diagnostics.rs
index 4304405b..9824bce0 100644
--- a/crates/tinymist-query/src/diagnostics.rs
+++ b/crates/tinymist-query/src/diagnostics.rs
@@ -46,8 +46,16 @@ impl<'w> DiagWorker<'w> {
         }
     }
 
-    /// Runs code check on the document.
-    pub fn check(mut self) -> Self {
+    /// Runs code check on the given document.
+    pub fn check(mut self, source: &Source) -> Self {
+        for diag in self.ctx.lint(&source) {
+            self.handle(&diag);
+        }
+        self
+    }
+
+    /// Runs code check on the main document and all its dependencies.
+    pub fn full_check(mut self) -> Self {
         for dep in self.ctx.world.depended_files() {
             if WorkspaceResolver::is_package_file(dep) {
                 continue;
diff --git a/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident.typ.snap b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident.typ.snap
new file mode 100644
index 00000000..85b38363
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident.typ.snap
@@ -0,0 +1,78 @@
+---
+source: crates/tinymist-query/src/code_action.rs
+description: "Code Action on $xy||z/* range "
+expression: "JsonRepr::new_redacted(result, &REDACT_LOC)"
+input_file: crates/tinymist-query/src/fixtures/code_action/unknown_math_ident.typ
+---
+[
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "\n\nlet xyz",
+      "range": "0:0:0:0"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Create missing variable"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "x y z",
+      "range": "0:1:0:4"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Add spaces between letters"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:4:0:22"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to block equation"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:4:0:22"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to multiple-line block equation"
+ }
+]
diff --git a/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident_frac.typ.snap b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident_frac.typ.snap
new file mode 100644
index 00000000..51a4d54c
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_ident_frac.typ.snap
@@ -0,0 +1,78 @@
+---
+source: crates/tinymist-query/src/code_action.rs
+description: Code Action on $a||b/c/* rang
+expression: "JsonRepr::new_redacted(result, &REDACT_LOC)"
+input_file: crates/tinymist-query/src/fixtures/code_action/unknown_math_ident_frac.typ
+---
+[
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "\n\nlet ab",
+      "range": "0:0:0:0"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Create missing variable"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "(a b)",
+      "range": "0:1:0:3"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Add spaces between letters"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:5:0:23"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to block equation"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:5:0:23"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to multiple-line block equation"
+ }
+]
diff --git a/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript.typ.snap b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript.typ.snap
new file mode 100644
index 00000000..e21e795a
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript.typ.snap
@@ -0,0 +1,78 @@
+---
+source: crates/tinymist-query/src/code_action.rs
+description: "Code Action on $a_i||j/* range "
+expression: "JsonRepr::new_redacted(result, &REDACT_LOC)"
+input_file: crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript.typ
+---
+[
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "\n\nlet ij",
+      "range": "0:0:0:0"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Create missing variable"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "(i j)",
+      "range": "0:3:0:5"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Add spaces between letters"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:5:0:23"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to block equation"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:5:0:23"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to multiple-line block equation"
+ }
+]
diff --git a/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript_paren.typ.snap b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript_paren.typ.snap
new file mode 100644
index 00000000..956cfc2f
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/snaps/test@unknown_math_subscript_paren.typ.snap
@@ -0,0 +1,78 @@
+---
+source: crates/tinymist-query/src/code_action.rs
+description: Code Action on $a_(i||j)/* range
+expression: "JsonRepr::new_redacted(result, &REDACT_LOC)"
+input_file: crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript_paren.typ
+---
+[
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "\n\nlet ij",
+      "range": "0:0:0:0"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Create missing variable"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 2,
+      "newText": "i j",
+      "range": "0:4:0:6"
+     }
+    ]
+   }
+  },
+  "kind": "quickfix",
+  "title": "Add spaces between letters"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": " ",
+      "range": "0:7:0:25"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to block equation"
+ },
+ {
+  "edit": {
+   "changes": {
+    "s0.typ": [
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:1:0:1"
+     },
+     {
+      "insertTextFormat": 1,
+      "newText": "\n",
+      "range": "0:7:0:25"
+     }
+    ]
+   }
+  },
+  "kind": "refactor.rewrite",
+  "title": "Convert to multiple-line block equation"
+ }
+]
diff --git a/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident.typ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident.typ
new file mode 100644
index 00000000..b4d94652
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident.typ
@@ -0,0 +1 @@
+$xyz/* range -1..-1 */$
diff --git a/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident_frac.typ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident_frac.typ
new file mode 100644
index 00000000..5c1ab385
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_ident_frac.typ
@@ -0,0 +1 @@
+$ab/c/* range -3..-3 */$
diff --git a/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript.typ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript.typ
new file mode 100644
index 00000000..0f32a345
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript.typ
@@ -0,0 +1 @@
+$a_ij/* range -1..-1 */$
diff --git a/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript_paren.typ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript_paren.typ
new file mode 100644
index 00000000..76330c4b
--- /dev/null
+++ b/crates/tinymist-query/src/fixtures/code_action/unknown_math_subscript_paren.typ
@@ -0,0 +1 @@
+$a_(ij)/* range -2..-2 */$