diff --git a/docs/developer_guides/chap03_index_service.md b/docs/developer_guides/chap03_index_service.md
index b64d7452b9..ca690afc65 100644
--- a/docs/developer_guides/chap03_index_service.md
+++ b/docs/developer_guides/chap03_index_service.md
@@ -21,6 +21,7 @@ type IndexCoord interface {
 	GetIndexStates(ctx context.Context, req *indexpb.GetIndexStatesRequest) (*indexpb.GetIndexStatesResponse, error)
 	// GetIndexFilePaths gets the index files of the IndexBuildIDs in the request from RootCoordinator.
 	GetIndexFilePaths(ctx context.Context, req *indexpb.GetIndexFilePathsRequest) (*indexpb.GetIndexFilePathsResponse, error)
+  // GetMetrics gets the metrics about IndexCoord.
 	GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error)
 }
 ```