diff --git a/studio/frontend/src/features/recipe-studio/components/inline/inline-expression.tsx b/studio/frontend/src/features/recipe-studio/components/inline/inline-expression.tsx
index 16a36d1ad5..206a068a78 100644
--- a/studio/frontend/src/features/recipe-studio/components/inline/inline-expression.tsx
+++ b/studio/frontend/src/features/recipe-studio/components/inline/inline-expression.tsx
@@ -9,6 +9,7 @@ import {
 import type { ReactElement } from "react";
 import { useRecipeStudioStore } from "../../stores/recipe-studio";
 import type { ExpressionConfig, ExpressionDtype } from "../../types";
+import { findInvalidJinjaReferences } from "../../utils/refs";
 import { getAvailableVariableEntries } from "../../utils/variables";
 import { AvailableReferencesInline } from "../shared/available-references-inline";
 import { InlineField } from "./inline-field";
@@ -26,6 +27,10 @@ export function InlineExpression({
 }: InlineExpressionProps): ReactElement {
   const configs = useRecipeStudioStore((state) => state.configs);
   const vars = getAvailableVariableEntries(configs, config.id);
+  const invalidRefs = findInvalidJinjaReferences(
+    config.expr,
+    vars.map((entry) => entry.name),
+  );
 
   return (
     <div className="space-y-3">
@@ -52,6 +57,7 @@ export function InlineExpression({
         <InlineField label="Expression">
           <Input
             className="nodrag h-8 w-full text-xs"
+            aria-invalid={invalidRefs.length > 0}
             placeholder="{{ column_name }}"
             value={config.expr}
             onChange={(event) => onUpdate({ expr: event.target.value })}
diff --git a/studio/frontend/src/features/recipe-studio/components/recipe-graph-aux-node.tsx b/studio/frontend/src/features/recipe-studio/components/recipe-graph-aux-node.tsx
index 2aa1988102..bbb5dead41 100644
--- a/studio/frontend/src/features/recipe-studio/components/recipe-graph-aux-node.tsx
+++ b/studio/frontend/src/features/recipe-studio/components/recipe-graph-aux-node.tsx
@@ -13,6 +13,7 @@ import { useRecipeStudioStore } from "../stores/recipe-studio";
 import type { LlmConfig, Score, ScoreOption } from "../types";
 import { AUX_HANDLE_CLASS } from "../utils/handle-layout";
 import { HANDLE_IDS } from "../utils/handles";
+import { findInvalidJinjaReferences } from "../utils/refs";
 import { getAvailableVariableEntries } from "../utils/variables";
 import { AvailableReferencesInline } from "./shared/available-references-inline";
 import { BaseNode, BaseNodeContent, BaseNodeHeader, BaseNodeHeaderTitle } from "./rf-ui/base-node";
@@ -56,10 +57,12 @@ function updateOptionAt(
   );
 }
 
-function AuxVariableBadges({ llmId }: { llmId: string }): ReactElement | null {
-  const configs = useRecipeStudioStore((state) => state.configs);
-  const vars = getAvailableVariableEntries(configs, llmId);
-  return <AvailableReferencesInline entries={vars} />;
+function AuxVariableBadges({
+  entries,
+}: {
+  entries: ReturnType<typeof getAvailableVariableEntries>;
+}): ReactElement | null {
+  return <AvailableReferencesInline entries={entries} />;
 }
 
 function AuxNodeBase({
@@ -67,6 +70,7 @@ function AuxNodeBase({
   data,
 }: NodeProps<RecipeGraphAuxNodeType>): ReactElement | null {
   const config = useRecipeStudioStore((state) => state.configs[data.llmId]);
+  const configs = useRecipeStudioStore((state) => state.configs);
   const updateConfig = useRecipeStudioStore((state) => state.updateConfig);
   const updateNodeInternals = useUpdateNodeInternals();
 
@@ -117,6 +121,10 @@ function AuxNodeBase({
 
   if (data.kind === "llm-prompt-input") {
     const value = data.field === "prompt" ? config.prompt : config.system_prompt;
+    const variableEntries = getAvailableVariableEntries(configs, data.llmId);
+    const availableRefs = variableEntries.map((entry) => entry.name);
+    const hasInvalidRefs =
+      findInvalidJinjaReferences(value, availableRefs).length > 0;
     return (
       <BaseNode className="corner-squircle w-full min-w-0 rounded-lg border-border/60 bg-card shadow-sm">
         <BaseNodeHeader className="border-b border-border/50 px-3 py-2">
@@ -125,6 +133,7 @@ function AuxNodeBase({
         <BaseNodeContent className="gap-2 px-3 py-2">
           <Textarea
             className="corner-squircle nodrag nowheel max-h-40 min-h-[88px] w-full resize-none overflow-y-auto text-xs"
+            aria-invalid={hasInvalidRefs}
             value={value}
             onChange={(event) =>
               updateConfig(data.llmId, {
@@ -132,7 +141,7 @@ function AuxNodeBase({
               } as Partial<LlmConfig>)
             }
           />
-          <AuxVariableBadges llmId={data.llmId} />
+          <AuxVariableBadges entries={variableEntries} />
         </BaseNodeContent>
         {sourceHandles}
       </BaseNode>
diff --git a/studio/frontend/src/features/recipe-studio/dialogs/expression/expression-dialog.tsx b/studio/frontend/src/features/recipe-studio/dialogs/expression/expression-dialog.tsx
index 76579eff38..c734f67fae 100644
--- a/studio/frontend/src/features/recipe-studio/dialogs/expression/expression-dialog.tsx
+++ b/studio/frontend/src/features/recipe-studio/dialogs/expression/expression-dialog.tsx
@@ -7,7 +7,11 @@ import {
 } from "@/components/ui/select";
 import { Textarea } from "@/components/ui/textarea";
 import type { ReactElement } from "react";
+import { useMemo } from "react";
+import { useRecipeStudioStore } from "../../stores/recipe-studio";
 import type { ExpressionConfig, ExpressionDtype } from "../../types";
+import { findInvalidJinjaReferences } from "../../utils/refs";
+import { getAvailableVariables } from "../../utils/variables";
 import { AvailableVariables } from "../shared/available-variables";
 import { FieldLabel } from "../shared/field-label";
 import { NameField } from "../shared/name-field";
@@ -23,8 +27,21 @@ export function ExpressionDialog({
   config,
   onUpdate,
 }: ExpressionDialogProps): ReactElement {
+  const configs = useRecipeStudioStore((state) => state.configs);
   const dtypeId = `${config.id}-dtype`;
   const exprId = `${config.id}-expr`;
+  const validReferences = useMemo(
+    () => getAvailableVariables(configs, config.id),
+    [configs, config.id],
+  );
+  const invalidExprRefs = useMemo(
+    () => findInvalidJinjaReferences(config.expr, validReferences),
+    [config.expr, validReferences],
+  );
+  const invalidExprText = invalidExprRefs
+    .slice(0, 3)
+    .map((ref) => `{{ ${ref} }}`)
+    .join(", ");
   const updateField = <K extends keyof ExpressionConfig>(
     key: K,
     value: ExpressionConfig[K],
@@ -71,10 +88,19 @@ export function ExpressionDialog({
         <Textarea
           id={exprId}
           className="corner-squircle nodrag"
+          aria-invalid={invalidExprRefs.length > 0}
           placeholder="{{ category_1 }} - {{ subcategory_1 }}"
           value={config.expr}
           onChange={(event) => updateField("expr", event.target.value)}
         />
+        {invalidExprRefs.length > 0 && (
+          <p className="text-xs text-destructive">
+            Unknown reference: {invalidExprText}
+            {invalidExprRefs.length > 3
+              ? ` +${invalidExprRefs.length - 3} more`
+              : ""}
+          </p>
+        )}
         <p className="text-xs text-muted-foreground">
           Use Jinja2. Reference columns like {"{{ column_name }}"}.
         </p>
diff --git a/studio/frontend/src/features/recipe-studio/dialogs/llm/general-tab.tsx b/studio/frontend/src/features/recipe-studio/dialogs/llm/general-tab.tsx
index 04960354f4..1fbf267d47 100644
--- a/studio/frontend/src/features/recipe-studio/dialogs/llm/general-tab.tsx
+++ b/studio/frontend/src/features/recipe-studio/dialogs/llm/general-tab.tsx
@@ -14,8 +14,11 @@ import {
   SelectValue,
 } from "@/components/ui/select";
 import { Textarea } from "@/components/ui/textarea";
-import { type ReactElement, type RefObject } from "react";
+import { type ReactElement, type RefObject, useMemo } from "react";
+import { useRecipeStudioStore } from "../../stores/recipe-studio";
 import type { LlmConfig } from "../../types";
+import { findInvalidJinjaReferences } from "../../utils/refs";
+import { getAvailableVariables } from "../../utils/variables";
 import { AvailableVariables } from "../shared/available-variables";
 import { FieldLabel } from "../shared/field-label";
 import { NameField } from "../shared/name-field";
@@ -54,6 +57,7 @@ export function LlmGeneralTab({
   modelAliasAnchorRef,
   onUpdate,
 }: LlmGeneralTabProps): ReactElement {
+  const configs = useRecipeStudioStore((state) => state.configs);
   const modelAliasId = `${config.id}-model-alias`;
   const codeLangId = `${config.id}-code-lang`;
   const promptId = `${config.id}-prompt`;
@@ -61,6 +65,26 @@ export function LlmGeneralTab({
   const systemPromptId = `${config.id}-system-prompt`;
   const hasModelConfigs = modelConfigAliases.length > 0;
   const hasModelProviders = modelProviderOptions.length > 0;
+  const validReferences = useMemo(
+    () => getAvailableVariables(configs, config.id),
+    [configs, config.id],
+  );
+  const invalidPromptRefs = useMemo(
+    () => findInvalidJinjaReferences(config.prompt, validReferences),
+    [config.prompt, validReferences],
+  );
+  const invalidSystemRefs = useMemo(
+    () => findInvalidJinjaReferences(config.system_prompt, validReferences),
+    [config.system_prompt, validReferences],
+  );
+  const invalidPromptText = invalidPromptRefs
+    .slice(0, 3)
+    .map((ref) => `{{ ${ref} }}`)
+    .join(", ");
+  const invalidSystemText = invalidSystemRefs
+    .slice(0, 3)
+    .map((ref) => `{{ ${ref} }}`)
+    .join(", ");
 
   return (
     <div className="space-y-4">
@@ -148,9 +172,18 @@ export function LlmGeneralTab({
         <Textarea
           id={promptId}
           className="corner-squircle nodrag max-h-[450px] overflow-auto"
+          aria-invalid={invalidPromptRefs.length > 0}
           value={config.prompt}
           onChange={(event) => onUpdate({ prompt: event.target.value })}
         />
+        {invalidPromptRefs.length > 0 && (
+          <p className="text-xs text-destructive">
+            Unknown reference: {invalidPromptText}
+            {invalidPromptRefs.length > 3
+              ? ` +${invalidPromptRefs.length - 3} more`
+              : ""}
+          </p>
+        )}
       </div>
       {config.llm_type === "structured" && (
         <div className="grid gap-2">
@@ -178,9 +211,18 @@ export function LlmGeneralTab({
         <Textarea
           id={systemPromptId}
           className="corner-squircle nodrag max-h-[450px] overflow-auto"
+          aria-invalid={invalidSystemRefs.length > 0}
           value={config.system_prompt}
           onChange={(event) => onUpdate({ system_prompt: event.target.value })}
         />
+        {invalidSystemRefs.length > 0 && (
+          <p className="text-xs text-destructive">
+            Unknown reference: {invalidSystemText}
+            {invalidSystemRefs.length > 3
+              ? ` +${invalidSystemRefs.length - 3} more`
+              : ""}
+          </p>
+        )}
       </div>
     </div>
   );
diff --git a/studio/frontend/src/features/recipe-studio/utils/refs.ts b/studio/frontend/src/features/recipe-studio/utils/refs.ts
index 91f0e8e869..50f6c5b25f 100644
--- a/studio/frontend/src/features/recipe-studio/utils/refs.ts
+++ b/studio/frontend/src/features/recipe-studio/utils/refs.ts
@@ -1,4 +1,7 @@
 const JINJA_REF_RE = /{{\s*([a-zA-Z_][a-zA-Z0-9_]*)\s*}}/g;
+const JINJA_EXPR_RE = /{{\s*([^{}]+?)\s*}}/g;
+const SIMPLE_JINJA_EXPR_RE = /^[a-zA-Z_][a-zA-Z0-9_.]*$/;
+const PLAIN_JINJA_EXPR_RE = /^[a-zA-Z0-9_.\s-]+$/;
 
 function escapeRegExp(value: string): string {
   return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
@@ -17,6 +20,37 @@ export function extractRefs(template: string): string[] {
   return Array.from(refs);
 }
 
+export function findInvalidJinjaReferences(
+  template: string,
+  validReferences: string[],
+): string[] {
+  if (!template) {
+    return [];
+  }
+  const validSet = new Set(
+    validReferences.map((name) => name.trim()).filter(Boolean),
+  );
+  const invalid = new Set<string>();
+
+  for (const match of template.matchAll(JINJA_EXPR_RE)) {
+    const expr = (match[1] ?? "").trim();
+    if (!expr) {
+      continue;
+    }
+    if (SIMPLE_JINJA_EXPR_RE.test(expr)) {
+      if (!validSet.has(expr)) {
+        invalid.add(expr);
+      }
+      continue;
+    }
+    if (PLAIN_JINJA_EXPR_RE.test(expr)) {
+      invalid.add(expr);
+    }
+  }
+
+  return Array.from(invalid);
+}
+
 export function replaceRef(
   template: string,
   from: string,