diff --git a/internal/translator/openai/claude/openai_claude_request.go b/internal/translator/openai/claude/openai_claude_request.go
index 5a769ca41..2498f2f6e 100644
--- a/internal/translator/openai/claude/openai_claude_request.go
+++ b/internal/translator/openai/claude/openai_claude_request.go
@@ -313,7 +313,7 @@ func ConvertClaudeRequestToOpenAI(modelName string, inputRawJSON []byte, stream
 
 			// Convert Anthropic input_schema to OpenAI function parameters
 			if inputSchema := tool.Get("input_schema"); inputSchema.Exists() {
-				openAIToolJSON, _ = sjson.SetBytes(openAIToolJSON, "function.parameters", inputSchema.Value())
+				openAIToolJSON, _ = sjson.SetBytes(openAIToolJSON, "function.parameters", normalizeObjectSchemaProperties(inputSchema.Value()))
 			}
 
 			toolsJSON, _ = sjson.SetRawBytes(toolsJSON, "-1", openAIToolJSON)
@@ -352,6 +352,28 @@ func ConvertClaudeRequestToOpenAI(modelName string, inputRawJSON []byte, stream
 	return out
 }
 
+func normalizeObjectSchemaProperties(schema any) any {
+	switch value := schema.(type) {
+	case map[string]any:
+		if schemaType, ok := value["type"].(string); ok && schemaType == "object" {
+			if _, ok := value["properties"]; !ok {
+				value["properties"] = map[string]any{}
+			}
+		}
+		for key, child := range value {
+			value[key] = normalizeObjectSchemaProperties(child)
+		}
+		return value
+	case []any:
+		for i, child := range value {
+			value[i] = normalizeObjectSchemaProperties(child)
+		}
+		return value
+	default:
+		return schema
+	}
+}
+
 func shouldMapClaudeThinkingToGPTReasoning(part gjson.Result) bool {
 	signature := part.Get("signature")
 	if !signature.Exists() || strings.TrimSpace(signature.String()) == "" {
diff --git a/internal/translator/openai/claude/openai_claude_request_test.go b/internal/translator/openai/claude/openai_claude_request_test.go
index 34de754de..cbc57b527 100644
--- a/internal/translator/openai/claude/openai_claude_request_test.go
+++ b/internal/translator/openai/claude/openai_claude_request_test.go
@@ -496,6 +496,47 @@ func TestConvertClaudeRequestToOpenAI_SystemMessageScenarios(t *testing.T) {
 	}
 }
 
+func TestConvertClaudeRequestToOpenAI_ToolSchemaAddsMissingObjectProperties(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "claude-3-opus",
+		"tools": [
+			{
+				"name": "empty_params",
+				"description": "No args",
+				"input_schema": {"type": "object"}
+			},
+			{
+				"name": "nested_params",
+				"description": "Nested args",
+				"input_schema": {
+					"type": "object",
+					"properties": {
+						"nested": {"type": "object"},
+						"items": {
+							"type": "array",
+							"items": {"type": "object"}
+						}
+					}
+				}
+			}
+		],
+		"messages": [{"role": "user", "content": "hello"}]
+	}`)
+
+	output := ConvertClaudeRequestToOpenAI("test-model", inputJSON, false)
+	outputJSON := gjson.ParseBytes(output)
+
+	if got := outputJSON.Get("tools.0.function.parameters.properties"); !got.Exists() || !got.IsObject() {
+		t.Fatalf("root object properties missing or invalid: %s", outputJSON.Get("tools.0.function.parameters").Raw)
+	}
+	if got := outputJSON.Get("tools.1.function.parameters.properties.nested.properties"); !got.Exists() || !got.IsObject() {
+		t.Fatalf("nested object properties missing or invalid: %s", outputJSON.Get("tools.1.function.parameters").Raw)
+	}
+	if got := outputJSON.Get("tools.1.function.parameters.properties.items.items.properties"); !got.Exists() || !got.IsObject() {
+		t.Fatalf("array item object properties missing or invalid: %s", outputJSON.Get("tools.1.function.parameters").Raw)
+	}
+}
+
 func TestConvertClaudeRequestToOpenAI_ToolResultOrderAndContent(t *testing.T) {
 	inputJSON := `{
 		"model": "claude-3-opus",