diff --git a/src/agents/base-agent.ts b/src/agents/base-agent.ts
index bb73df6..edbffcb 100644
--- a/src/agents/base-agent.ts
+++ b/src/agents/base-agent.ts
@@ -97,22 +97,20 @@ export abstract class BaseAgent<TSession extends BaseSession> {
         return '__PASSTHROUGH__';
       }
 
-      // 5. Single-shot: execute tool calls returned by AI
+      // 5. Single-shot: execute tool calls, then synthesize via AI
       let finalResponse = aiResult.response;
       if (this.getExecutionStrategy() === 'single-shot'
         && aiResult.toolCalls && aiResult.toolCalls.length > 0) {
-        const toolResults: string[] = [];
+        const toolCallResults: Array<{ name: string; args: Record<string, unknown>; result: string }> = [];
         for (const tc of aiResult.toolCalls) {
           const result = await this.executeToolCall(tc.name, tc.arguments, session, context);
-          toolResults.push(result);
+          toolCallResults.push({ name: tc.name, args: tc.arguments, result });
           aiResult.calledTools.push(tc.name);
         }
-        if (toolResults.length > 0) {
-          const cleanAiText = (aiResult.response || '')
-            .replace('__SESSION_END__', '').trim();
-          finalResponse = cleanAiText
-            ? cleanAiText + '\n\n' + toolResults.join('\n\n')
-            : toolResults.join('\n\n');
+        if (toolCallResults.length > 0 && env.OPENAI_API_KEY) {
+          finalResponse = await this.synthesizeToolResults(
+            session, userMessage, aiResult.response, toolCallResults, env
+          );
         }
       }
 
@@ -149,6 +147,75 @@ export abstract class BaseAgent<TSession extends BaseSession> {
     }
   }
 
+  // --- Synthesize tool results into natural language ---
+
+  private async synthesizeToolResults(
+    session: TSession,
+    userMessage: string,
+    aiText: string,
+    toolResults: Array<{ name: string; args: Record<string, unknown>; result: string }>,
+    env: Env
+  ): Promise<string> {
+    const log = createLogger(this.agentName);
+
+    try {
+      const systemPrompt = this.getSystemPrompt(session) + this.buildPromptSuffix(session);
+      const toolSummary = toolResults
+        .map(tr => `[${tr.name}] 결과:\n${tr.result}`)
+        .join('\n\n');
+
+      const messages = [
+        { role: 'system', content: systemPrompt },
+        ...session.messages.map(m => ({
+          role: m.role === 'user' ? 'user' as const : 'assistant' as const,
+          content: m.content,
+        })),
+        { role: 'user', content: userMessage },
+        {
+          role: 'assistant',
+          content: aiText || '도구를 호출하여 정보를 조회했습니다.',
+        },
+        {
+          role: 'user',
+          content: `위 도구 실행 결과를 바탕으로 고객에게 보기 좋게 안내해주세요. JSON을 그대로 보여주지 말고 자연어로 정리하세요.\n\n${toolSummary}`,
+        },
+      ];
+
+      const controller = new AbortController();
+      const timeoutId = setTimeout(() => controller.abort(), 15000);
+
+      try {
+        const response = await fetch(getOpenAIUrl(env), {
+          method: 'POST',
+          headers: {
+            'Content-Type': 'application/json',
+            'Authorization': `Bearer ${env.OPENAI_API_KEY}`,
+          },
+          signal: controller.signal,
+          body: JSON.stringify({
+            model: AI_CONFIG.model,
+            messages,
+            max_tokens: this.getMaxTokens(),
+            temperature: this.getTemperature(),
+          }),
+        });
+
+        if (!response.ok) {
+          log.error('Synthesize API error', new Error(`HTTP ${response.status}`));
+          return toolResults.map(tr => tr.result).join('\n\n');
+        }
+
+        const data = await response.json() as OpenAIAPIResponse;
+        return data.choices[0].message.content || toolResults.map(tr => tr.result).join('\n\n');
+      } finally {
+        clearTimeout(timeoutId);
+      }
+    } catch (error) {
+      log.error('Tool result synthesis failed', error as Error);
+      return toolResults.map(tr => tr.result).join('\n\n');
+    }
+  }
+
   // --- AI Call Loop ---
 
   protected async callExpertAI(