diff --git a/buffer/file.md b/buffer/file.md
index 0d2db317..573cc9b7 100644
--- a/buffer/file.md
+++ b/buffer/file.md
@@ -2,6 +2,11 @@
 
 The `file` buffer plugin provides a persistent buffer implementation. It uses files to store buffer chunks on disk.
 
+{% hint style='info' %}
+In the following examples, it assumes pre-configured chunk keys by default with `<buffer>`.
+If you want to understand buffer behavior precisely, see [Buffer Section Configuration](../configuration/buffer-section.md) documentation.
+{% endhint %}
+
 ## Parameters
 
 * [Common Parameters](../configuration/plugin-common-parameters.md)
diff --git a/buffer/file_single.md b/buffer/file_single.md
index c623d823..90d99fd0 100644
--- a/buffer/file_single.md
+++ b/buffer/file_single.md
@@ -4,6 +4,11 @@ The `file_single` buffer plugin provides a persistent buffer implementation. It
 
 `file_single` is similar to `file_file` but it does not have the metadata file.
 
+{% hint style='info' %}
+In the following examples, it assumes pre-configured chunk keys by default with `<buffer>`.
+If you want to understand buffer behavior precisely, see [Buffer Section Configuration](../configuration/buffer-section.md) documentation.
+{% endhint %}
+
 ## Example Configuration
 
 ```text
diff --git a/buffer/memory.md b/buffer/memory.md
index faca37a3..126edea1 100644
--- a/buffer/memory.md
+++ b/buffer/memory.md
@@ -2,6 +2,11 @@
 
 The `memory` buffer plugin provides a fast buffer implementation. It uses memory to store buffer chunks. When Fluentd is shut down, buffered logs that cannot be written quickly are deleted.
 
+{% hint style='info' %}
+In the following examples, it assumes pre-configured chunk keys by default with `<buffer>`.
+If you want to understand buffer behavior precisely, see [Buffer Section Configuration](../configuration/buffer-section.md) documentation.
+{% endhint %}
+
 ## Parameters
 
 * [Common Parameters](../configuration/plugin-common-parameters.md)