diff --git a/backend/internal/pkg/antigravity/claude_types.go b/backend/internal/pkg/antigravity/claude_types.go
index 9cab4cea..01b805cd 100644
--- a/backend/internal/pkg/antigravity/claude_types.go
+++ b/backend/internal/pkg/antigravity/claude_types.go
@@ -37,8 +37,19 @@ type ClaudeMetadata struct {
 }
 
 // ClaudeTool Claude 工具定义
+// 支持两种格式：
+// 1. 标准格式: { "name": "...", "description": "...", "input_schema": {...} }
+// 2. Custom 格式 (MCP): { "type": "custom", "name": "...", "custom": { "description": "...", "input_schema": {...} } }
 type ClaudeTool struct {
-	Name        string         `json:"name"`
+	Type        string          `json:"type,omitempty"` // "custom" 或空（标准格式）
+	Name        string          `json:"name"`
+	Description string          `json:"description,omitempty"`  // 标准格式使用
+	InputSchema map[string]any  `json:"input_schema,omitempty"` // 标准格式使用
+	Custom      *CustomToolSpec `json:"custom,omitempty"`       // custom 格式使用
+}
+
+// CustomToolSpec MCP custom 工具规格
+type CustomToolSpec struct {
 	Description string         `json:"description,omitempty"`
 	InputSchema map[string]any `json:"input_schema"`
 }
diff --git a/backend/internal/pkg/antigravity/request_transformer.go b/backend/internal/pkg/antigravity/request_transformer.go
index 2ff0ec02..e0b5b886 100644
--- a/backend/internal/pkg/antigravity/request_transformer.go
+++ b/backend/internal/pkg/antigravity/request_transformer.go
@@ -3,6 +3,7 @@ package antigravity
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"strings"
 
 	"github.com/google/uuid"
@@ -205,6 +206,13 @@ func buildParts(content json.RawMessage, toolIDToName map[string]string, allowDu
 			// 保留原有 signature（Claude 模型需要有效的 signature）
 			if block.Signature != "" {
 				part.ThoughtSignature = block.Signature
+			} else if !allowDummyThought {
+				// Claude 模型需要有效 signature，跳过无 signature 的 thinking block
+				log.Printf("Warning: skipping thinking block without signature for Claude model")
+				continue
+			} else {
+				// Gemini 模型使用 dummy signature
+				part.ThoughtSignature = dummyThoughtSignature
 			}
 			parts = append(parts, part)
 
@@ -379,12 +387,40 @@ func buildTools(tools []ClaudeTool) []GeminiToolDeclaration {
 	// 普通工具
 	var funcDecls []GeminiFunctionDecl
 	for _, tool := range tools {
+		// 跳过无效工具名称
+		if tool.Name == "" {
+			log.Printf("Warning: skipping tool with empty name")
+			continue
+		}
+
+		var description string
+		var inputSchema map[string]any
+
+		// 检查是否为 custom 类型工具 (MCP)
+		if tool.Type == "custom" && tool.Custom != nil {
+			// Custom 格式: 从 custom 字段获取 description 和 input_schema
+			description = tool.Custom.Description
+			inputSchema = tool.Custom.InputSchema
+		} else {
+			// 标准格式: 从顶层字段获取
+			description = tool.Description
+			inputSchema = tool.InputSchema
+		}
+
 		// 清理 JSON Schema
-		params := cleanJSONSchema(tool.InputSchema)
+		params := cleanJSONSchema(inputSchema)
+
+		// 为 nil schema 提供默认值
+		if params == nil {
+			params = map[string]any{
+				"type":       "OBJECT",
+				"properties": map[string]any{},
+			}
+		}
 
 		funcDecls = append(funcDecls, GeminiFunctionDecl{
 			Name:        tool.Name,
-			Description: tool.Description,
+			Description: description,
 			Parameters:  params,
 		})
 	}
diff --git a/backend/internal/service/gemini_messages_compat_service.go b/backend/internal/service/gemini_messages_compat_service.go
index ee3ade16..a0bf1b6a 100644
--- a/backend/internal/service/gemini_messages_compat_service.go
+++ b/backend/internal/service/gemini_messages_compat_service.go
@@ -2245,12 +2245,40 @@ func convertClaudeToolsToGeminiTools(tools any) []any {
 		if !ok {
 			continue
 		}
-		name, _ := tm["name"].(string)
-		desc, _ := tm["description"].(string)
-		params := tm["input_schema"]
+
+		var name, desc string
+		var params any
+
+		// 检查是否为 custom 类型工具 (MCP)
+		toolType, _ := tm["type"].(string)
+		if toolType == "custom" {
+			// Custom 格式: 从 custom 字段获取 description 和 input_schema
+			custom, ok := tm["custom"].(map[string]any)
+			if !ok {
+				continue
+			}
+			name, _ = tm["name"].(string)
+			desc, _ = custom["description"].(string)
+			params = custom["input_schema"]
+		} else {
+			// 标准格式: 从顶层字段获取
+			name, _ = tm["name"].(string)
+			desc, _ = tm["description"].(string)
+			params = tm["input_schema"]
+		}
+
 		if name == "" {
 			continue
 		}
+
+		// 为 nil params 提供默认值
+		if params == nil {
+			params = map[string]any{
+				"type":       "object",
+				"properties": map[string]any{},
+			}
+		}
+
 		funcDecls = append(funcDecls, map[string]any{
 			"name":        name,
 			"description": desc,