diff --git a/package/visualization/plot_contour/README.md b/package/visualization/plot_contour/README.md
index 31079903..efeabdb9 100644
--- a/package/visualization/plot_contour/README.md
+++ b/package/visualization/plot_contour/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Contour Plot'
 description: 'Plot the parameter relationship as contour plot in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_edf/README.md b/package/visualization/plot_edf/README.md
index 6b14ecca..ce2256ff 100644
--- a/package/visualization/plot_edf/README.md
+++ b/package/visualization/plot_edf/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Empirical Distribution Function Plot'
 description: 'Plot the objective value EDF (empirical distribution function) of a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_hypervolume_history/README.md b/package/visualization/plot_hypervolume_history/README.md
index 6a1916a4..fd67fcbb 100644
--- a/package/visualization/plot_hypervolume_history/README.md
+++ b/package/visualization/plot_hypervolume_history/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Hypervolume History Plot'
 description: 'Plot hypervolume history of all trials in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_intermediate_values/README.md b/package/visualization/plot_intermediate_values/README.md
index d06b6013..36ad2339 100644
--- a/package/visualization/plot_intermediate_values/README.md
+++ b/package/visualization/plot_intermediate_values/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Intermediate Values Plot'
 description: 'Plot intermediate values of all trials in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_optimization_history/README.md b/package/visualization/plot_optimization_history/README.md
index bf99f530..acba814c 100644
--- a/package/visualization/plot_optimization_history/README.md
+++ b/package/visualization/plot_optimization_history/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Optimization History Plot'
 description: 'Plot optimization history of all trials in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_parallel_coordinate/README.md b/package/visualization/plot_parallel_coordinate/README.md
index a815a457..495f72b5 100644
--- a/package/visualization/plot_parallel_coordinate/README.md
+++ b/package/visualization/plot_parallel_coordinate/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Parallel Coordinate Plot'
 description: 'Plot the high-dimensional parameter relationships in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_param_importances/README.md b/package/visualization/plot_param_importances/README.md
index 6b1c203d..746796be 100644
--- a/package/visualization/plot_param_importances/README.md
+++ b/package/visualization/plot_param_importances/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Hyperparameter Importances Plot'
 description: 'Plot hyperparameter importances.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_pareto_front/README.md b/package/visualization/plot_pareto_front/README.md
index ff8f662b..a3d8a1bf 100644
--- a/package/visualization/plot_pareto_front/README.md
+++ b/package/visualization/plot_pareto_front/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Pareto-front Plot'
 description: 'Plot the Pareto front of a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_rank/README.md b/package/visualization/plot_rank/README.md
index e1485956..3cfbd958 100644
--- a/package/visualization/plot_rank/README.md
+++ b/package/visualization/plot_rank/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Rank Plot'
 description: 'Plot parameter relations as scatter plots with colors indicating ranks of target value.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_slice/README.md b/package/visualization/plot_slice/README.md
index 2410ed3d..dac58e8f 100644
--- a/package/visualization/plot_slice/README.md
+++ b/package/visualization/plot_slice/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Slice Plot'
 description: 'Plot the parameter relationship as slice plot in a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_terminator_improvement/README.md b/package/visualization/plot_terminator_improvement/README.md
index adfdb256..aef31816 100644
--- a/package/visualization/plot_terminator_improvement/README.md
+++ b/package/visualization/plot_terminator_improvement/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Terminator Improvement Plot'
 description: 'Plot the potentials for future objective improvement.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---
diff --git a/package/visualization/plot_timeline/README.md b/package/visualization/plot_timeline/README.md
index 396c5a49..c5c96f5c 100644
--- a/package/visualization/plot_timeline/README.md
+++ b/package/visualization/plot_timeline/README.md
@@ -2,7 +2,7 @@
 author: 'Optuna team'
 title: 'Timeline Plot'
 description: 'Plot the timeline of a study.'
-tags: ['visualization']
+tags: ['visualization', "built-in"]
 optuna_versions: ['3.6.1']
 license: 'MIT License'
 ---