diff --git a/backend/internal/service/gemini_messages_compat_service.go b/backend/internal/service/gemini_messages_compat_service.go
index 5b1abc11..45aa3599 100644
--- a/backend/internal/service/gemini_messages_compat_service.go
+++ b/backend/internal/service/gemini_messages_compat_service.go
@@ -3169,12 +3169,17 @@ func convertClaudeToolsToGeminiTools(tools any) []any {
 		return nil
 	}
 
+	hasWebSearch := false
 	funcDecls := make([]any, 0, len(arr))
 	for _, t := range arr {
 		tm, ok := t.(map[string]any)
 		if !ok {
 			continue
 		}
+		if isClaudeWebSearchToolMap(tm) {
+			hasWebSearch = true
+			continue
+		}
 
 		var name, desc string
 		var params any
@@ -3218,13 +3223,35 @@ func convertClaudeToolsToGeminiTools(tools any) []any {
 		})
 	}
 
-	if len(funcDecls) == 0 {
+	out := make([]any, 0, 2)
+	if len(funcDecls) > 0 {
+		out = append(out, map[string]any{
+			"functionDeclarations": funcDecls,
+		})
+	}
+	if hasWebSearch {
+		out = append(out, map[string]any{
+			"googleSearch": map[string]any{},
+		})
+	}
+	if len(out) == 0 {
 		return nil
 	}
-	return []any{
-		map[string]any{
-			"functionDeclarations": funcDecls,
-		},
+	return out
+}
+
+func isClaudeWebSearchToolMap(tool map[string]any) bool {
+	toolType, _ := tool["type"].(string)
+	if strings.HasPrefix(toolType, "web_search") || toolType == "google_search" {
+		return true
+	}
+
+	name, _ := tool["name"].(string)
+	switch strings.TrimSpace(name) {
+	case "web_search", "google_search", "web_search_20250305":
+		return true
+	default:
+		return false
 	}
 }
 
diff --git a/backend/internal/service/gemini_messages_compat_service_test.go b/backend/internal/service/gemini_messages_compat_service_test.go
index f659f0e6..0d132b48 100644
--- a/backend/internal/service/gemini_messages_compat_service_test.go
+++ b/backend/internal/service/gemini_messages_compat_service_test.go
@@ -164,6 +164,35 @@ func TestConvertClaudeToolsToGeminiTools_CustomType(t *testing.T) {
 	}
 }
 
+func TestConvertClaudeToolsToGeminiTools_PreservesWebSearchAlongsideFunctions(t *testing.T) {
+	tools := []any{
+		map[string]any{
+			"name":         "get_weather",
+			"description":  "Get weather info",
+			"input_schema": map[string]any{"type": "object"},
+		},
+		map[string]any{
+			"type": "web_search_20250305",
+			"name": "web_search",
+		},
+	}
+
+	result := convertClaudeToolsToGeminiTools(tools)
+	require.Len(t, result, 2)
+
+	functionDecl, ok := result[0].(map[string]any)
+	require.True(t, ok)
+	funcDecls, ok := functionDecl["functionDeclarations"].([]any)
+	require.True(t, ok)
+	require.Len(t, funcDecls, 1)
+
+	searchDecl, ok := result[1].(map[string]any)
+	require.True(t, ok)
+	googleSearch, ok := searchDecl["googleSearch"].(map[string]any)
+	require.True(t, ok)
+	require.Empty(t, googleSearch)
+}
+
 func TestGeminiHandleNativeNonStreamingResponse_DebugDisabledDoesNotEmitHeaderLogs(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	logSink, restore := captureStructuredLog(t)