diff --git a/viz-core/src/body.rs b/viz-core/src/body.rs
index ecb37c4d..99e0108a 100644
--- a/viz-core/src/body.rs
+++ b/viz-core/src/body.rs
@@ -9,8 +9,8 @@ use hyper::body::{Body, Frame, Incoming, SizeHint};
 
 use crate::{Bytes, Error, Result};
 
-#[derive(Debug)]
 /// Incoming Body from request.
+#[derive(Debug)]
 pub enum IncomingBody {
     /// A empty body.
     Empty,
@@ -107,8 +107,8 @@ impl Stream for IncomingBody {
     }
 }
 
-#[derive(Debug)]
 /// Outgoing Body to response.
+#[derive(Debug)]
 pub enum OutgoingBody<D = Bytes> {
     /// A empty body.
     Empty,
diff --git a/viz-core/src/middleware/cookie.rs b/viz-core/src/middleware/cookie.rs
index 4fcb5244..4ba4a39b 100644
--- a/viz-core/src/middleware/cookie.rs
+++ b/viz-core/src/middleware/cookie.rs
@@ -15,8 +15,8 @@ pub struct Config {
 }
 
 impl Config {
-    #[cfg(any(feature = "cookie-signed", feature = "cookie-private"))]
     /// Creates a new config with the [`Key`][types::CookieKey].
+    #[cfg(any(feature = "cookie-signed", feature = "cookie-private"))]
     #[must_use]
     pub fn with_key(key: types::CookieKey) -> Self {
         Self {
diff --git a/viz-core/src/middleware/helper.rs b/viz-core/src/middleware/helper.rs
index 4b3630f9..351729aa 100644
--- a/viz-core/src/middleware/helper.rs
+++ b/viz-core/src/middleware/helper.rs
@@ -123,8 +123,8 @@ impl Default for CookieOptions {
     }
 }
 
-#[cfg(not(feature = "cookie-private"))]
 /// An interface for managing the cookies.
+#[cfg(not(feature = "cookie-private"))]
 pub trait Cookieable {
     /// Gets the options of the cookie.
     fn options(&self) -> &CookieOptions;
@@ -145,8 +145,8 @@ pub trait Cookieable {
     }
 }
 
-#[cfg(feature = "cookie-private")]
 /// An interface for managing the `private` cookies.
+#[cfg(feature = "cookie-private")]
 pub trait Cookieable {
     /// Gets the options of the cookie.
     fn options(&self) -> &CookieOptions;
diff --git a/viz-core/src/middleware/limits.rs b/viz-core/src/middleware/limits.rs
index 3fb37c68..2591ff41 100644
--- a/viz-core/src/middleware/limits.rs
+++ b/viz-core/src/middleware/limits.rs
@@ -27,8 +27,8 @@ impl Config {
         self
     }
 
-    #[cfg(feature = "multipart")]
     /// Sets a limits for the Multipart Form.
+    #[cfg(feature = "multipart")]
     #[must_use]
     pub fn multipart(mut self, limits: types::MultipartLimits) -> Self {
         *Arc::make_mut(&mut self.multipart) = limits;
diff --git a/viz-core/src/request.rs b/viz-core/src/request.rs
index c21b635e..19d795cf 100644
--- a/viz-core/src/request.rs
+++ b/viz-core/src/request.rs
@@ -129,8 +129,8 @@ pub trait RequestExt: Sized {
     #[cfg(feature = "multipart")]
     async fn multipart(&mut self) -> Result<Multipart, PayloadError>;
 
-    #[cfg(feature = "state")]
     /// Return a shared state by the specified type.
+    #[cfg(feature = "state")]
     fn state<T>(&self) -> Option<T>
     where
         T: Clone + Send + Sync + 'static;
diff --git a/viz-core/src/response.rs b/viz-core/src/response.rs
index 16decb52..b685c5f1 100644
--- a/viz-core/src/response.rs
+++ b/viz-core/src/response.rs
@@ -1,5 +1,3 @@
-#[cfg(feature = "json")]
-use bytes::{BufMut, BytesMut};
 use http_body_util::Full;
 
 use crate::{header, Bytes, Error, OutgoingBody, Response, Result, StatusCode};
@@ -40,17 +38,20 @@ pub trait ResponseExt: Sized {
         Self::with(body.into(), mime::TEXT_HTML_UTF_8.as_ref())
     }
 
-    #[cfg(feature = "json")]
     /// The response with `application/javascript; charset=utf-8` media type.
     ///
     /// # Errors
     ///
     /// Throws an error if serialization fails.
+    #[cfg(feature = "json")]
     fn json<T>(body: T) -> Result<Response, crate::types::PayloadError>
     where
         T: serde::Serialize,
     {
-        let mut buf = BytesMut::new().writer();
+        use bytes::{BufMut, BytesMut};
+
+        // See <https://docs.rs/serde_json/latest/src/serde_json/ser.rs.html#2179>
+        let mut buf = BytesMut::with_capacity(128).writer();
         serde_json::to_writer(&mut buf, &body)
             .map(|()| {
                 Self::with(