diff --git a/frontend/src/components/workspace/input-box-helpers.ts b/frontend/src/components/workspace/input-box-helpers.ts
index f89610eb6..d771654aa 100644
--- a/frontend/src/components/workspace/input-box-helpers.ts
+++ b/frontend/src/components/workspace/input-box-helpers.ts
@@ -1,10 +1,11 @@
 import type { Skill } from "@/core/skills";
+export {
+  SUGGESTION_TEMPLATE_PLACEHOLDER_PATTERN,
+  findSuggestionTemplatePlaceholder,
+} from "@/core/suggestions/placeholders";
 
 export const MAX_SKILL_SUGGESTIONS = 6;
 
-export const SUGGESTION_TEMPLATE_PLACEHOLDER_PATTERN =
-  /\[(?:主题|来源|topic|source)\]/i;
-
 export type SlashSuggestion = {
   name: string;
   description: string;
@@ -100,18 +101,6 @@ export function isAbortError(error: unknown): boolean {
   );
 }
 
-export function findSuggestionTemplatePlaceholder(text: string) {
-  const match = SUGGESTION_TEMPLATE_PLACEHOLDER_PATTERN.exec(text);
-  if (!match) {
-    return null;
-  }
-
-  return {
-    start: match.index,
-    end: match.index + match[0].length,
-  };
-}
-
 export function getLeadingSlashSkillQuery(value: string): string | null {
   if (!value.startsWith("/")) {
     return null;
diff --git a/frontend/src/components/workspace/input-box.tsx b/frontend/src/components/workspace/input-box.tsx
index fcd4cb016..60403925a 100644
--- a/frontend/src/components/workspace/input-box.tsx
+++ b/frontend/src/components/workspace/input-box.tsx
@@ -23,7 +23,6 @@ import {
   useState,
   type ComponentProps,
   type KeyboardEvent,
-  type RefObject,
 } from "react";
 import { toast } from "sonner";
 
@@ -614,7 +613,7 @@ export function InputBox({
       }
       const placeholder = findSuggestionTemplatePlaceholder(message.text);
       if (placeholder) {
-        toast.error(t.inputBox.suggestionPlaceholderRequired);
+        toast.warning(t.inputBox.suggestionPlaceholderRequired);
         requestAnimationFrame(() => {
           const textarea = textareaRef.current;
           if (!textarea) {
@@ -1069,6 +1068,18 @@ export function InputBox({
     threadId,
   ]);
 
+  const onSelectPlaceholder = useCallback((newText: string) => {
+    const placeholder = findSuggestionTemplatePlaceholder(newText);
+    if (placeholder) {
+      requestAnimationFrame(() => {
+        const textarea = textareaRef.current;
+        if (!textarea) return;
+        textarea.focus();
+        textarea.setSelectionRange(placeholder.start, placeholder.end);
+      });
+    }
+  }, []);
+
   return (
     <div
       ref={promptRootRef}
@@ -1568,7 +1579,7 @@ export function InputBox({
         searchParams.get("mode") !== "skill" &&
         !showSkillSuggestions && (
           <div className="flex items-center justify-center pt-2">
-            <SuggestionList textareaRef={textareaRef} />
+            <SuggestionList onSelectPlaceholder={onSelectPlaceholder} />
           </div>
         )}
 
@@ -1598,9 +1609,9 @@ export function InputBox({
 }
 
 function SuggestionList({
-  textareaRef,
+  onSelectPlaceholder,
 }: {
-  textareaRef: RefObject<HTMLTextAreaElement | null>;
+  onSelectPlaceholder: (newText: string) => void;
 }) {
   const { t } = useI18n();
   const { textInput } = usePromptInputController();
@@ -1608,16 +1619,9 @@ function SuggestionList({
     (prompt: string | undefined) => {
       if (!prompt) return;
       textInput.setInput(prompt);
-      requestAnimationFrame(() => {
-        const textarea = textareaRef.current;
-        const placeholder = findSuggestionTemplatePlaceholder(prompt);
-        if (textarea && placeholder) {
-          textarea.focus();
-          textarea.setSelectionRange(placeholder.start, placeholder.end);
-        }
-      });
+      onSelectPlaceholder(prompt);
     },
-    [textareaRef, textInput],
+    [textInput, onSelectPlaceholder],
   );
   return (
     <Suggestions className="min-h-16 w-full max-w-full justify-center px-4 sm:w-fit sm:px-0">
diff --git a/frontend/src/core/suggestions/placeholders.ts b/frontend/src/core/suggestions/placeholders.ts
new file mode 100644
index 000000000..70d5a6c85
--- /dev/null
+++ b/frontend/src/core/suggestions/placeholders.ts
@@ -0,0 +1,30 @@
+/**
+ * Regex matching known suggestion template placeholders.
+ *
+ * These are the exact placeholder tokens used in suggestion prompt templates
+ * defined in the i18n locale files (e.g., zh-CN.ts, en-US.ts).
+ *
+ * Update this pattern whenever new placeholder tokens are added to templates.
+ */
+export const SUGGESTION_TEMPLATE_PLACEHOLDER_PATTERN =
+  /\[(?:主题|来源|topic|source)\]/i;
+
+/**
+ * Locates an unreplaced suggestion template placeholder in the given text.
+ *
+ * Returns the start/end character indices of the placeholder if found,
+ * or `null` if the text contains no known placeholder tokens.
+ */
+export function findSuggestionTemplatePlaceholder(
+  text: string,
+): { start: number; end: number } | null {
+  const match = SUGGESTION_TEMPLATE_PLACEHOLDER_PATTERN.exec(text);
+  if (!match) {
+    return null;
+  }
+
+  return {
+    start: match.index,
+    end: match.index + match[0].length,
+  };
+}
diff --git a/frontend/tests/unit/core/suggestions/placeholders.test.ts b/frontend/tests/unit/core/suggestions/placeholders.test.ts
new file mode 100644
index 000000000..3d6192492
--- /dev/null
+++ b/frontend/tests/unit/core/suggestions/placeholders.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, test } from "@rstest/core";
+
+import { findSuggestionTemplatePlaceholder } from "@/core/suggestions/placeholders";
+
+describe("findSuggestionTemplatePlaceholder", () => {
+  test("finds Chinese [主题] and returns correct range", () => {
+    const result = findSuggestionTemplatePlaceholder(
+      "深入浅出的研究一下[主题]，并总结发现。",
+    );
+    expect(result).toEqual({ start: 9, end: 13 });
+  });
+
+  test("finds English [topic] and returns correct range", () => {
+    const result = findSuggestionTemplatePlaceholder(
+      "Write a blog post about the latest trends on [topic]",
+    );
+    expect(result).toEqual({ start: 45, end: 52 });
+  });
+
+  test("finds Chinese [来源] placeholder", () => {
+    const result =
+      findSuggestionTemplatePlaceholder("从[来源]收集数据并创建报告。");
+    expect(result).not.toBeNull();
+  });
+
+  test("finds English [source] placeholder", () => {
+    const result = findSuggestionTemplatePlaceholder(
+      "Collect data from [source] and create a report.",
+    );
+    expect(result).not.toBeNull();
+  });
+
+  test("returns null for normal text without brackets", () => {
+    expect(
+      findSuggestionTemplatePlaceholder("研究一下2025年最流行的Python框架"),
+    ).toBeNull();
+  });
+
+  test("returns null for text with unrelated brackets", () => {
+    expect(
+      findSuggestionTemplatePlaceholder("check [this link] for details"),
+    ).toBeNull();
+  });
+
+  test("returns null for empty text", () => {
+    expect(findSuggestionTemplatePlaceholder("")).toBeNull();
+  });
+
+  test("detects placeholder case-insensitively for English", () => {
+    expect(
+      findSuggestionTemplatePlaceholder("Research [Topic] deeply"),
+    ).not.toBeNull();
+    expect(
+      findSuggestionTemplatePlaceholder("Research [TOPIC] deeply"),
+    ).not.toBeNull();
+  });
+});