diff --git a/Cargo.lock b/Cargo.lock
index 2c3b7d5..8ee425f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -260,6 +260,8 @@ name = "cch23-8bit"
 version = "0.1.0"
 dependencies = [
  "axum 0.7.1",
+ "serde",
+ "serde_json",
  "shuttle-axum",
  "shuttle-runtime",
  "tokio",
diff --git a/Cargo.toml b/Cargo.toml
index 94be6ed..9196f30 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,6 +5,8 @@ edition = "2021"
 
 [dependencies]
 axum = "0.7.1"
+serde = { version = "1.0.193", features = ["derive"] }
+serde_json = "1.0.108"
 shuttle-axum = { version = "0.34.1", default-features = false, features = ["axum-0-7"] }
 shuttle-runtime = "0.34.1"
 tokio = "1.34.0"
diff --git a/src/cal/day04.rs b/src/cal/day04.rs
new file mode 100644
index 0000000..e8523cc
--- /dev/null
+++ b/src/cal/day04.rs
@@ -0,0 +1,71 @@
+use axum::{extract::Json, response::IntoResponse, routing::post, Router};
+
+pub(crate) fn router() -> Router {
+    Router::new()
+        .route("/4/strength", post(strength))
+        .route("/4/contest", post(contest))
+}
+
+#[allow(dead_code)]
+#[derive(serde::Deserialize)]
+struct Reindeer {
+    name: String,
+    strength: i32,
+}
+
+async fn strength(Json(reindeer): Json<Vec<Reindeer>>) -> impl IntoResponse {
+    reindeer
+        .into_iter()
+        .map(|r| r.strength)
+        .sum::<i32>()
+        .to_string()
+}
+
+#[derive(serde::Deserialize)]
+struct AdvReindeer {
+    name: String,
+    strength: i32,
+    speed: f32,
+    height: i32,
+    antler_width: i32,
+    snow_magic_power: i32,
+    favorite_food: String,
+    #[serde(rename = "cAnD13s_3ATeN-yesT3rdAy")]
+    candies: i32,
+}
+
+#[derive(serde::Serialize)]
+struct ContestResult {
+    fastest: String,
+    tallest: String,
+    magician: String,
+    consumer: String,
+}
+
+async fn contest(Json(reindeer): Json<Vec<AdvReindeer>>) -> Json<ContestResult> {
+    let fastest = reindeer
+        .iter()
+        .max_by(|l, r| l.speed.total_cmp(&r.speed))
+        .unwrap();
+    let tallest = reindeer.iter().max_by_key(|r| r.height).unwrap();
+    let magician = reindeer.iter().max_by_key(|r| r.snow_magic_power).unwrap();
+    let consumer = reindeer.iter().max_by_key(|r| r.candies).unwrap();
+    Json(ContestResult {
+        fastest: format!(
+            "Speeding past the finish line with a strength of {} is {}",
+            fastest.strength, fastest.name
+        ),
+        tallest: format!(
+            "{} is standing tall with his {} cm wide antlers",
+            tallest.name, tallest.antler_width
+        ),
+        magician: format!(
+            "{} could blast you away with a snow magic power of {}",
+            magician.name, magician.snow_magic_power
+        ),
+        consumer: format!(
+            "{} ate lots of candies, but also some {}",
+            consumer.name, consumer.favorite_food
+        ),
+    })
+}
diff --git a/src/cal/mod.rs b/src/cal/mod.rs
index 3384629..52a3bd8 100644
--- a/src/cal/mod.rs
+++ b/src/cal/mod.rs
@@ -1,8 +1,10 @@
 mod day00;
 mod day01;
+mod day04;
 
 pub(crate) fn router() -> axum::Router {
     axum::Router::new()
         .nest("/", day00::router())
         .nest("/", day01::router())
+        .nest("/", day04::router())
 }