diff --git a/src/app/service/agent/core/providers/anthropic.test.ts b/src/app/service/agent/core/providers/anthropic.test.ts
index ceec67698..36697e7b9 100644
--- a/src/app/service/agent/core/providers/anthropic.test.ts
+++ b/src/app/service/agent/core/providers/anthropic.test.ts
@@ -555,4 +555,24 @@ describe("parseAnthropicStream", () => {
     expect(events).toHaveLength(2);
     expect(events[0]).toEqual({ type: "content_delta", delta: "ok" });
   });
+
+  it("tool_use block 的 input_json_delta 應帶上 id 和 index", async () => {
+    const reader = createMockReader([
+      'event: content_block_start\ndata: {"index":1,"content_block":{"type":"tool_use","id":"toolu_X","name":"f"}}\n\n',
+      'event: content_block_delta\ndata: {"index":1,"delta":{"type":"input_json_delta","partial_json":"{\\"a\\":1}"}}\n\n',
+      "event: message_stop\ndata: {}\n\n",
+    ]);
+
+    const events: ChatStreamEvent[] = [];
+    const controller = new AbortController();
+
+    await parseAnthropicStream(reader, (e) => events.push(e), controller.signal);
+
+    const d = events.find((e) => e.type === "tool_call_delta");
+    expect(d).toBeDefined();
+    if (d && d.type === "tool_call_delta") {
+      expect(d.id).toBe("toolu_X");
+      expect(d.index).toBe(1);
+    }
+  });
 });
diff --git a/src/app/service/agent/core/providers/anthropic.ts b/src/app/service/agent/core/providers/anthropic.ts
index b12a1792b..27486e164 100644
--- a/src/app/service/agent/core/providers/anthropic.ts
+++ b/src/app/service/agent/core/providers/anthropic.ts
@@ -187,6 +187,8 @@ export function parseAnthropicStream(
   // 跟踪图片块的累积 base64 数据
   let imageBlockData: { index: number; mediaType: string; base64Chunks: string[] } | null = null;
 
+  const toolUseByIndex = new Map<number, { id: string }>();
+
   return readSSEStream(
     reader,
     signal,
@@ -212,6 +214,7 @@ export function parseAnthropicStream(
             if (block?.type === "thinking") {
               // thinking block 开始，后续通过 content_block_delta 传输内容
             } else if (block?.type === "tool_use") {
+              toolUseByIndex.set(json.index, { id: block.id });
               onEvent({
                 type: "tool_call_start",
                 toolCall: {
@@ -245,9 +248,11 @@ export function parseAnthropicStream(
             } else if (delta?.type === "thinking_delta") {
               onEvent({ type: "thinking_delta", delta: delta.thinking });
             } else if (delta?.type === "input_json_delta") {
+              const tu = toolUseByIndex.get(json.index);
               onEvent({
                 type: "tool_call_delta",
-                id: "",
+                id: tu?.id || "",
+                index: json.index,
                 delta: delta.partial_json,
               });
             } else if (delta?.type === "image_delta" && imageBlockData) {
@@ -274,6 +279,10 @@ export function parseAnthropicStream(
               });
               imageBlockData = null;
             }
+            // tool_use block 结束后清理 index→id 映射，避免长会话下 map 持续增长
+            if (typeof json.index === "number") {
+              toolUseByIndex.delete(json.index);
+            }
             break;
           }
           case "message_delta": {
@@ -293,6 +302,7 @@ export function parseAnthropicStream(
             break;
           }
           case "message_stop": {
+            toolUseByIndex.clear();
             onEvent({ type: "done" });
             return true;
           }
diff --git a/src/app/service/agent/core/providers/openai.test.ts b/src/app/service/agent/core/providers/openai.test.ts
index a62b9fdf6..b145895fc 100644
--- a/src/app/service/agent/core/providers/openai.test.ts
+++ b/src/app/service/agent/core/providers/openai.test.ts
@@ -361,20 +361,25 @@ describe("parseOpenAIStream", () => {
 
     await parseOpenAIStream(reader, (e) => events.push(e), controller.signal);
 
-    expect(events).toHaveLength(3);
+    expect(events).toHaveLength(4);
     expect(events[0].type).toBe("tool_call_start");
     if (events[0].type === "tool_call_start") {
       expect(events[0].toolCall.name).toBe("dom_read_page");
-      expect(events[0].toolCall.arguments).toBe('{"tabId":123');
+      // 新行为：start 事件的 args 永远为空，首 chunk 的 args 通过 delta 发出
+      expect(events[0].toolCall.arguments).toBe("");
     }
-    // 关键：最后的 tool_call_delta 不应被 usage 检查吞掉
     expect(events[1].type).toBe("tool_call_delta");
     if (events[1].type === "tool_call_delta") {
-      expect(events[1].delta).toBe(',"mode":"summary"}');
+      expect(events[1].delta).toBe('{"tabId":123'); // 故意的 — 模拟 streaming 还没收完的状态
     }
-    expect(events[2].type).toBe("done");
-    if (events[2].type === "done") {
-      expect(events[2].usage).toEqual({ inputTokens: 40010, outputTokens: 154 });
+    // 关键：最后的 tool_call_delta 不应被 usage 检查吞掉
+    expect(events[2].type).toBe("tool_call_delta");
+    if (events[2].type === "tool_call_delta") {
+      expect(events[2].delta).toBe(',"mode":"summary"}');
+    }
+    expect(events[3].type).toBe("done");
+    if (events[3].type === "done") {
+      expect(events[3].usage).toEqual({ inputTokens: 40010, outputTokens: 154 });
     }
   });
 
@@ -529,13 +534,84 @@ describe("parseOpenAIStream", () => {
 
     await parseOpenAIStream(reader, (e) => events.push(e), controller.signal);
 
-    expect(events).toHaveLength(4);
+    expect(events).toHaveLength(5);
     expect(events[0]).toEqual({ type: "thinking_delta", delta: "分析页面" });
     expect(events[1]).toEqual({ type: "thinking_delta", delta: "结构" });
     expect(events[2].type).toBe("tool_call_start");
-    expect(events[3].type).toBe("done");
-    if (events[3].type === "done") {
-      expect(events[3].usage).toEqual({ inputTokens: 500, outputTokens: 50 });
+    if (events[2].type === "tool_call_start") {
+      expect(events[2].toolCall.name).toBe("dom_read_page");
+      expect(events[2].toolCall.arguments).toBe("");
+    }
+    expect(events[3].type).toBe("tool_call_delta");
+    if (events[3].type === "tool_call_delta") {
+      expect(events[3].delta).toBe('{"selector":".item"}');
+    }
+    expect(events[4].type).toBe("done");
+    if (events[4].type === "done") {
+      expect(events[4].usage).toEqual({ inputTokens: 500, outputTokens: 50 });
     }
   });
+
+  it("首 chunk 同时带 name 和 arguments 时：start 事件 args 为空，首 chunk args 作为 delta 发出", async () => {
+    const reader = createMockReader([
+      // gateway / 某些 model 会先发一个 arguments="{}" 占位再送真正 JSON
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_x","function":{"name":"agent","arguments":"{}"}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{\\"description\\":\\"r\\""}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":",\\"prompt\\":\\"do\\"}"}}]}}]}\n\n',
+      "data: [DONE]\n\n",
+    ]);
+    const events: ChatStreamEvent[] = [];
+    await parseOpenAIStream(reader, (e) => events.push(e), new AbortController().signal);
+
+    expect(events[0].type).toBe("tool_call_start");
+    if (events[0].type === "tool_call_start") {
+      // 关键断言：start 事件里的 args 必须为空，不能是 "{}"（避免前缀污染）
+      expect(events[0].toolCall.arguments).toBe("");
+      expect(events[0].toolCall.name).toBe("agent");
+    }
+    // 首 chunk 的 "{}" 作为第一段 delta 原样透传（模型问题：整体非合法 JSON，但解析器不吞字符）
+    const deltas = events.filter((e) => e.type === "tool_call_delta");
+    expect(deltas).toHaveLength(3);
+    expect(deltas[0].type === "tool_call_delta" && deltas[0].delta).toBe("{}");
+    expect(deltas[1].type === "tool_call_delta" && deltas[1].delta).toBe('{"description":"r"');
+    expect(deltas[2].type === "tool_call_delta" && deltas[2].delta).toBe(',"prompt":"do"}');
+  });
+
+  it("并发多个 tool_call（不同 index）arguments 不应互相串扰", async () => {
+    const reader = createMockReader([
+      // 两个 tool 同时开始
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"a","function":{"name":"f1","arguments":""}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":1,"id":"b","function":{"name":"f2","arguments":""}}]}}]}\n\n',
+      // 然后交错发 arguments delta（只带 index，不带 id）
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{\\"x\\":1}"}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":1,"function":{"arguments":"{\\"y\\":2}"}}]}}]}\n\n',
+      "data: [DONE]\n\n",
+    ]);
+    const events: ChatStreamEvent[] = [];
+    await parseOpenAIStream(reader, (e) => events.push(e), new AbortController().signal);
+    // 基础断言：两个 start + 两个 delta + done
+    const starts = events.filter((e) => e.type === "tool_call_start");
+    expect(starts).toHaveLength(2);
+    // （完整的 index 匹配需要 ChatStreamEvent 增加 index 字段，这里先确保 parser 不丢 event）
+  });
+
+  it("并行 tool_call 按 index 正确分派 arguments", async () => {
+    const reader = createMockReader([
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"a","function":{"name":"f1","arguments":""}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":1,"id":"b","function":{"name":"f2","arguments":""}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":1,"function":{"arguments":"{\\"y\\":2}"}}]}}]}\n\n',
+      'data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{\\"x\\":1}"}}]}}]}\n\n',
+      "data: [DONE]\n\n",
+    ]);
+    const events: ChatStreamEvent[] = [];
+    await parseOpenAIStream(reader, (e) => events.push(e), new AbortController().signal);
+
+    const deltas = events.filter((e) => e.type === "tool_call_delta");
+    expect(deltas).toHaveLength(2);
+    // 第一个 delta 对应 index=1（因为到达顺序）
+    expect((deltas[0] as any).index).toBe(1);
+    expect((deltas[0] as any).delta).toBe('{"y":2}');
+    expect((deltas[1] as any).index).toBe(0);
+    expect((deltas[1] as any).delta).toBe('{"x":1}');
+  });
 });
diff --git a/src/app/service/agent/core/providers/openai.ts b/src/app/service/agent/core/providers/openai.ts
index d1004eeff..619c14a17 100644
--- a/src/app/service/agent/core/providers/openai.ts
+++ b/src/app/service/agent/core/providers/openai.ts
@@ -263,19 +263,23 @@ export function parseOpenAIStream(
             // 工具调用
             if (delta.tool_calls) {
               for (const tc of delta.tool_calls) {
+                // OpenAI 约定：第一个 chunk 带 id + function.name，后续 chunk 只带 index + function.arguments
                 if (tc.function?.name) {
                   onEvent({
                     type: "tool_call_start",
                     toolCall: {
-                      id: tc.id || `tc_${Date.now()}`,
+                      id: tc.id || `tc_${Date.now()}_${tc.index ?? 0}`,
                       name: tc.function.name,
-                      arguments: tc.function.arguments || "",
+                      arguments: "", // 永远空启动，避免首 chunk 的 "{}" 作为 prefix 污染
                     },
                   });
-                } else if (tc.function?.arguments) {
+                }
+                // 首 chunk 带 arguments 也作为 delta 处理（不 else if！）
+                if (tc.function?.arguments !== undefined && tc.function.arguments !== "") {
                   onEvent({
                     type: "tool_call_delta",
-                    id: tc.id || "",
+                    id: tc.id || "", // 后续 chunk 大概率无 id，这里只保留接口兼容
+                    index: tc.index, // 用于匹配的字段
                     delta: tc.function.arguments,
                   });
                 }
diff --git a/src/app/service/agent/core/types.ts b/src/app/service/agent/core/types.ts
index 3afc4b0c5..54574d295 100644
--- a/src/app/service/agent/core/types.ts
+++ b/src/app/service/agent/core/types.ts
@@ -117,7 +117,7 @@ export type LLMStreamEvent =
   | { type: "content_delta"; delta: string }
   | { type: "thinking_delta"; delta: string }
   | { type: "tool_call_start"; toolCall: Omit<ToolCall, "result"> }
-  | { type: "tool_call_delta"; id: string; delta: string }
+  | { type: "tool_call_delta"; id: string; delta: string; index?: number }
   | { type: "tool_call_complete"; id: string; result: string; attachments?: Attachment[] }
   | { type: "content_block_start"; block: Omit<ImageBlock | FileBlock | AudioBlock, "attachmentId"> }
   | { type: "content_block_complete"; block: ImageBlock | FileBlock | AudioBlock; data?: string };
diff --git a/src/app/service/agent/service_worker/background.test.ts b/src/app/service/agent/service_worker/background.test.ts
index 4089d6b14..82db11843 100644
--- a/src/app/service/agent/service_worker/background.test.ts
+++ b/src/app/service/agent/service_worker/background.test.ts
@@ -410,6 +410,21 @@ describe("handleAttachToConversation 重连逻辑", () => {
 
     (service as any).bgSessionManager.delete("conv-empty");
   });
+
+  it("tool_call_delta 按 index 分派給正確的 tool call", () => {
+    const { service } = createTestService();
+    const rc = createRunningConversation();
+    const upd = (service as any).bgSessionManager.updateStreamingState.bind((service as any).bgSessionManager);
+
+    upd(rc, { type: "tool_call_start", toolCall: { id: "a", name: "f1", arguments: "" } });
+    upd(rc, { type: "tool_call_start", toolCall: { id: "b", name: "f2", arguments: "" } });
+    // 交錯到達
+    upd(rc, { type: "tool_call_delta", id: "", index: 1, delta: '{"y":2}' });
+    upd(rc, { type: "tool_call_delta", id: "", index: 0, delta: '{"x":1}' });
+
+    expect(rc.streamingState.toolCalls[0].arguments).toBe('{"x":1}');
+    expect(rc.streamingState.toolCalls[1].arguments).toBe('{"y":2}');
+  });
 });
 
 // ---- 后台运行会话 集成测试 ----
diff --git a/src/app/service/agent/service_worker/background_session_manager.ts b/src/app/service/agent/service_worker/background_session_manager.ts
index 7a7de4025..de92f558e 100644
--- a/src/app/service/agent/service_worker/background_session_manager.ts
+++ b/src/app/service/agent/service_worker/background_session_manager.ts
@@ -57,12 +57,35 @@ export class BackgroundSessionManager {
       case "tool_call_start":
         rc.streamingState.toolCalls.push({ ...event.toolCall, status: "running" });
         break;
-      case "tool_call_delta":
-        if (rc.streamingState.toolCalls.length > 0) {
-          const last = rc.streamingState.toolCalls[rc.streamingState.toolCalls.length - 1];
-          last.arguments += event.delta;
+      case "tool_call_delta": {
+        // 按 id 匹配（fallback 到最新 running 的 tc），不再盲目取 length-1。
+        // 并发 tool call 时（OpenAI 用 index 区分、Anthropic 的多个 tool_use block）length-1 会把 delta 写错工具。
+        if (rc.streamingState.toolCalls.length === 0) break;
+
+        let target: ToolCall | undefined = undefined;
+        // 1a. 按 id 匹配
+        if (event.id) {
+          target = rc.streamingState.toolCalls.find((t) => t.id === event.id);
         }
+        // 1b. 按 index 匹配（OpenAI 后续 chunk 无 id 只有 index）
+        if (!target && event.index !== undefined) {
+          target = rc.streamingState.toolCalls[event.index];
+        }
+
+        // 2. fallback：最新一个状态为 running 的 tool call
+        //    （OpenAI 后续 chunk 不带 id，但同一 index 的 tool 一定在 running）
+        if (!target) {
+          for (let i = rc.streamingState.toolCalls.length - 1; i >= 0; i--) {
+            if (rc.streamingState.toolCalls[i].status === "running") {
+              target = rc.streamingState.toolCalls[i];
+              break;
+            }
+          }
+        }
+
+        if (target) target.arguments += event.delta;
         break;
+      }
       case "tool_call_complete": {
         const tc = rc.streamingState.toolCalls.find((t) => t.id === event.id);
         if (tc) {
diff --git a/src/app/service/agent/service_worker/llm_client.ts b/src/app/service/agent/service_worker/llm_client.ts
index db79652db..ec076f115 100644
--- a/src/app/service/agent/service_worker/llm_client.ts
+++ b/src/app/service/agent/service_worker/llm_client.ts
@@ -128,7 +128,6 @@ export class LLMClient {
     let content = "";
     let thinking = "";
     const toolCalls: ToolCall[] = [];
-    let currentToolCall: ToolCall | null = null;
     let usage:
       | { inputTokens: number; outputTokens: number; cacheCreationInputTokens?: number; cacheReadInputTokens?: number }
       | undefined;
@@ -157,23 +156,34 @@ export class LLMClient {
             thinking += event.delta;
             break;
           case "tool_call_start":
-            // 如果已有一个正在收集的 tool call，先保存它（多个 tool_use 并行返回时）
-            if (currentToolCall) {
-              toolCalls.push(currentToolCall);
-            }
-            currentToolCall = { ...event.toolCall, arguments: event.toolCall.arguments || "" };
+            // 并发 tool_call 时 parser 会交错发 delta，这里立即 push 到数组，
+            // 由 tool_call_delta 通过 id/index 定位目标 tool，避免串扰。
+            toolCalls.push({ ...event.toolCall, arguments: event.toolCall.arguments || "", status: "running" });
             break;
-          case "tool_call_delta":
-            if (currentToolCall) {
-              currentToolCall.arguments += event.delta;
+          case "tool_call_delta": {
+            if (!toolCalls.length) break;
+            let target: ToolCall | undefined = undefined;
+            // 1a. 按 id 匹配
+            if (event.id) {
+              target = toolCalls.find((t) => t.id === event.id);
+            }
+            // 1b. 按 index 匹配（OpenAI 后续 chunk 无 id 只有 index）
+            if (!target && event.index !== undefined) {
+              target = toolCalls[event.index];
             }
+            // 2. fallback：最新一个状态为 running 的 tool call
+            if (!target) {
+              for (let i = toolCalls.length - 1; i >= 0; i--) {
+                if (toolCalls[i].status === "running") {
+                  target = toolCalls[i];
+                  break;
+                }
+              }
+            }
+            if (target) target.arguments += event.delta;
             break;
+          }
           case "done": {
-            // 保存当前的 tool call
-            if (currentToolCall) {
-              toolCalls.push(currentToolCall);
-              currentToolCall = null;
-            }
             if (event.usage) {
               usage = event.usage;
             }
diff --git a/src/app/service/agent/service_worker/sub_agent_service.ts b/src/app/service/agent/service_worker/sub_agent_service.ts
index fc3e18463..0cb7a8194 100644
--- a/src/app/service/agent/service_worker/sub_agent_service.ts
+++ b/src/app/service/agent/service_worker/sub_agent_service.ts
@@ -138,11 +138,21 @@ export class SubAgentService {
             status: "running",
           });
           break;
-        case "tool_call_delta":
-          if (currentMsg.toolCalls.length) {
-            currentMsg.toolCalls[currentMsg.toolCalls.length - 1].arguments += event.delta;
+        case "tool_call_delta": {
+          if (!currentMsg.toolCalls.length) break;
+          let t = event.id ? currentMsg.toolCalls.find((x) => x.id === event.id) : undefined;
+          if (!t && event.index !== undefined) t = currentMsg.toolCalls[event.index];
+          if (!t) {
+            for (let i = currentMsg.toolCalls.length - 1; i >= 0; i--) {
+              if (currentMsg.toolCalls[i].status === "running") {
+                t = currentMsg.toolCalls[i];
+                break;
+              }
+            }
           }
+          if (t) t.arguments += event.delta;
           break;
+        }
         case "tool_call_complete": {
           const tc = currentMsg.toolCalls.find((t) => t.id === event.id);
           if (tc) {
diff --git a/src/pages/options/routes/AgentChat/ChatArea.tsx b/src/pages/options/routes/AgentChat/ChatArea.tsx
index 362e6be00..32f5998ad 100644
--- a/src/pages/options/routes/AgentChat/ChatArea.tsx
+++ b/src/pages/options/routes/AgentChat/ChatArea.tsx
@@ -179,11 +179,21 @@ export default function ChatArea({
           case "tool_call_start":
             sa.currentToolCalls.push({ ...event.toolCall, status: "running" });
             break;
-          case "tool_call_delta":
-            if (sa.currentToolCalls.length) {
-              sa.currentToolCalls[sa.currentToolCalls.length - 1].arguments += event.delta;
+          case "tool_call_delta": {
+            if (!sa.currentToolCalls.length) break;
+            let t = event.id ? sa.currentToolCalls.find((x) => x.id === event.id) : undefined;
+            if (!t && event.index !== undefined) t = sa.currentToolCalls[event.index];
+            if (!t) {
+              for (let i = sa.currentToolCalls.length - 1; i >= 0; i--) {
+                if (sa.currentToolCalls[i].status === "running") {
+                  t = sa.currentToolCalls[i];
+                  break;
+                }
+              }
             }
+            if (t) t.arguments += event.delta;
             break;
+          }
           case "tool_call_complete": {
             const tc = sa.currentToolCalls.find((t) => t.id === event.id);
             if (tc) {
@@ -271,12 +281,21 @@ export default function ChatArea({
           if (!msg.toolCalls) msg.toolCalls = [];
           msg.toolCalls.push({ ...event.toolCall, status: "running" });
           break;
-        case "tool_call_delta":
-          if (msg.toolCalls?.length) {
-            const lastTc = msg.toolCalls[msg.toolCalls.length - 1];
-            lastTc.arguments += event.delta;
+        case "tool_call_delta": {
+          if (!msg.toolCalls?.length) break;
+          let t = event.id ? msg.toolCalls.find((x) => x.id === event.id) : undefined;
+          if (!t && event.index !== undefined) t = msg.toolCalls[event.index];
+          if (!t) {
+            for (let i = msg.toolCalls.length - 1; i >= 0; i--) {
+              if (msg.toolCalls[i].status === "running") {
+                t = msg.toolCalls[i];
+                break;
+              }
+            }
           }
+          if (t) t.arguments += event.delta;
           break;
+        }
         case "tool_call_complete": {
           const tc = msg.toolCalls?.find((t) => t.id === event.id);
           if (tc) {