diff --git a/API.en.md b/API.en.md
index 678e6b0..122d9c9 100644
--- a/API.en.md
+++ b/API.en.md
@@ -167,6 +167,7 @@ When `tools` is present, DS2API injects a tool prompt and parses tool-call paylo
 
 - Non-stream: if detected, returns `message.tool_calls`, `finish_reason=tool_calls`, and `message.content=null`
 - Stream: to avoid leaking raw tool-call JSON, DS2API buffers text first; if tool call is detected, only structured `delta.tool_calls` is emitted
+- Stream `delta.tool_calls` is strict-client compatible: each tool call object includes `index` (starting from `0`)
 
 Tool-call response example:
 
diff --git a/API.md b/API.md
index 55f34e5..e66ba30 100644
--- a/API.md
+++ b/API.md
@@ -171,6 +171,7 @@ data: [DONE]
 
 - 非流式：若识别到工具调用，返回 `message.tool_calls`，并设置 `finish_reason=tool_calls`，`message.content=null`
 - 流式：为防止原始 toolcall JSON 泄漏，正文会先缓冲；若识别到工具调用，仅输出结构化 `delta.tool_calls`
+- 流式 `delta.tool_calls` 兼容严格客户端：每个 tool call 对象都带 `index`（从 `0` 开始）
 
 工具调用响应示例：
 
diff --git a/DEPLOY.en.md b/DEPLOY.en.md
index 503efa7..bf09b31 100644
--- a/DEPLOY.en.md
+++ b/DEPLOY.en.md
@@ -94,6 +94,25 @@ This repo includes `.github/workflows/release-artifacts.yml`:
 - Builds Linux/macOS/Windows archives and uploads them to Release Assets
 - Generates `sha256sums.txt` for integrity checks
 
+## 3.2 Vercel Build Troubleshooting
+
+If you see an error like:
+
+```text
+Error: Command failed: go build -ldflags -s -w -o .../bootstrap .../main__vc__go__.go
+```
+
+it is usually caused by invalid Go build flag settings in Vercel
+(`-ldflags` not passed as a single argument).
+
+How to fix:
+
+1. Open Vercel Project Settings -> Build and Development Settings
+2. Clear custom Go Build Flags / Build Command (recommended)
+3. If ldflags must be used, set `-ldflags=\"-s -w\"` so it is passed as one argument
+4. Ensure `go.mod` uses a supported version (this repo uses `go 1.24`)
+5. Redeploy (preferably with cache cleared)
+
 ## 4. Reverse Proxy (Nginx)
 
 Disable buffering for SSE:
diff --git a/DEPLOY.md b/DEPLOY.md
index 1ccc080..fa75a36 100644
--- a/DEPLOY.md
+++ b/DEPLOY.md
@@ -94,6 +94,24 @@ docker-compose up -d --build
 - 自动构建 Linux/macOS/Windows 二进制包并上传到 Release Assets
 - 生成 `sha256sums.txt` 供校验
 
+## 3.2 Vercel 常见报错排查
+
+若看到类似报错：
+
+```text
+Error: Command failed: go build -ldflags -s -w -o .../bootstrap .../main__vc__go__.go
+```
+
+通常是 Vercel 项目里的 Go 构建参数配置不正确（`-ldflags` 没有作为一个整体字符串传递）。
+
+处理方式：
+
+1. 进入 Vercel Project Settings -> Build and Development Settings
+2. 清空自定义 Go Build Flags / Build Command（推荐）
+3. 若必须设置 ldflags，使用 `-ldflags=\"-s -w\"`（保证它是一个参数）
+4. 确认仓库 `go.mod` 为受支持版本（当前为 `go 1.24`）
+5. 重新部署（建议 `Redeploy` 并清缓存）
+
 ## 4. 反向代理（Nginx）
 
 如果在 Nginx 后挂载，建议关闭缓冲以保证 SSE：
diff --git a/internal/adapter/openai/handler.go b/internal/adapter/openai/handler.go
index d507849..d497659 100644
--- a/internal/adapter/openai/handler.go
+++ b/internal/adapter/openai/handler.go
@@ -246,7 +246,7 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 		if len(detected) > 0 {
 			finishReason = "tool_calls"
 			delta := map[string]any{
-				"tool_calls": util.FormatOpenAIToolCalls(detected),
+				"tool_calls": util.FormatOpenAIStreamToolCalls(detected),
 			}
 			if !firstChunkSent {
 				delta["role"] = "assistant"
diff --git a/internal/adapter/openai/handler_toolcall_test.go b/internal/adapter/openai/handler_toolcall_test.go
index df39d51..6bc8d30 100644
--- a/internal/adapter/openai/handler_toolcall_test.go
+++ b/internal/adapter/openai/handler_toolcall_test.go
@@ -209,6 +209,24 @@ func TestHandleStreamToolCallInterceptsWithoutRawContentLeak(t *testing.T) {
 	if !streamHasToolCallsDelta(frames) {
 		t.Fatalf("expected tool_calls delta, body=%s", rec.Body.String())
 	}
+	foundToolIndex := false
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			toolCalls, _ := delta["tool_calls"].([]any)
+			for _, tc := range toolCalls {
+				tcm, _ := tc.(map[string]any)
+				if _, ok := tcm["index"].(float64); ok {
+					foundToolIndex = true
+				}
+			}
+		}
+	}
+	if !foundToolIndex {
+		t.Fatalf("expected stream tool_calls item with index, body=%s", rec.Body.String())
+	}
 	if streamHasRawToolJSONContent(frames) {
 		t.Fatalf("raw tool_calls JSON leaked in content delta: %s", rec.Body.String())
 	}
@@ -236,6 +254,24 @@ func TestHandleStreamReasonerToolCallInterceptsWithoutRawContentLeak(t *testing.
 	if !streamHasToolCallsDelta(frames) {
 		t.Fatalf("expected tool_calls delta, body=%s", rec.Body.String())
 	}
+	foundToolIndex := false
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			toolCalls, _ := delta["tool_calls"].([]any)
+			for _, tc := range toolCalls {
+				tcm, _ := tc.(map[string]any)
+				if _, ok := tcm["index"].(float64); ok {
+					foundToolIndex = true
+				}
+			}
+		}
+	}
+	if !foundToolIndex {
+		t.Fatalf("expected stream tool_calls item with index, body=%s", rec.Body.String())
+	}
 	if streamHasRawToolJSONContent(frames) {
 		t.Fatalf("raw tool_calls JSON leaked in content delta: %s", rec.Body.String())
 	}
@@ -277,6 +313,24 @@ func TestHandleStreamUnknownToolStillIntercepted(t *testing.T) {
 	if !streamHasToolCallsDelta(frames) {
 		t.Fatalf("expected tool_calls delta, body=%s", rec.Body.String())
 	}
+	foundToolIndex := false
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			toolCalls, _ := delta["tool_calls"].([]any)
+			for _, tc := range toolCalls {
+				tcm, _ := tc.(map[string]any)
+				if _, ok := tcm["index"].(float64); ok {
+					foundToolIndex = true
+				}
+			}
+		}
+	}
+	if !foundToolIndex {
+		t.Fatalf("expected stream tool_calls item with index, body=%s", rec.Body.String())
+	}
 	if streamHasRawToolJSONContent(frames) {
 		t.Fatalf("raw tool_calls JSON leaked in content delta: %s", rec.Body.String())
 	}
diff --git a/internal/util/toolcalls.go b/internal/util/toolcalls.go
index a594a6a..9b9d4e6 100644
--- a/internal/util/toolcalls.go
+++ b/internal/util/toolcalls.go
@@ -298,3 +298,20 @@ func FormatOpenAIToolCalls(calls []ParsedToolCall) []map[string]any {
 	}
 	return out
 }
+
+func FormatOpenAIStreamToolCalls(calls []ParsedToolCall) []map[string]any {
+	out := make([]map[string]any, 0, len(calls))
+	for i, c := range calls {
+		args, _ := json.Marshal(c.Input)
+		out = append(out, map[string]any{
+			"index": i,
+			"id":    "call_" + strings.ReplaceAll(uuid.NewString(), "-", ""),
+			"type":  "function",
+			"function": map[string]any{
+				"name":      c.Name,
+				"arguments": string(args),
+			},
+		})
+	}
+	return out
+}