diff --git a/Cargo.lock b/Cargo.lock
index b056181..bdc1fc5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -519,6 +519,12 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7655c9839580ee829dfacba1d1278c2b7883e50a277ff7541299489d6bdfdc45"
 
+[[package]]
+name = "itoa"
+version = "1.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1a46d1a171d865aa5f83f92695765caa047a9b4cbae2cbf37dbd613a793fd4c"
+
 [[package]]
 name = "libc"
 version = "0.2.153"
@@ -581,6 +587,28 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "mini-internal"
+version = "0.1.38"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f09fa787e06d071d09c2964b065eb7cb1b842a7af5382fc4c9142089f8383f08"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "miniserde"
+version = "0.1.38"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e19a2e17a11c24d44c84d7e1b61477e20cd503d024e4b0eb3e97eb9a4d24fa87"
+dependencies = [
+ "itoa",
+ "mini-internal",
+ "ryu",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.7.2"
@@ -685,6 +713,7 @@ version = "0.1.0"
 dependencies = [
  "futures",
  "miette",
+ "miniserde",
  "smol",
 ]
 
@@ -730,6 +759,12 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "ryu"
+version = "1.0.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e86697c916019a8588c99b5fac3cead74ec0b4b819707a682fd4d23fa0ce1ba1"
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.4.1"
diff --git a/Cargo.toml b/Cargo.toml
index 7edcf37..f4850f8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,4 +6,5 @@ edition = "2021"
 [dependencies]
 futures = "0.3.30"
 miette = { version = "5", features = ["fancy"] }
+miniserde = "0.1.38"
 smol = "1.3.0"
diff --git a/src/main.rs b/src/main.rs
index 5ab77da..2ec8c79 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,9 +1,161 @@
-use futures::{AsyncReadExt, StreamExt};
+use futures::{
+    future::ready, io::BufReader, AsyncBufReadExt, AsyncReadExt, AsyncWriteExt, StreamExt,
+    TryStreamExt,
+};
 use miette::IntoDiagnostic;
+use miniserde::{json::Number, Deserialize, Serialize};
+
+fn pow(a: u64, d: u64, n: u64) -> u64 {
+    let n: u128 = n.into();
+    let mut d: u128 = d.into();
+    let mut x: u128 = 1;
+    let mut q: u128 = a.into();
+    while d != 0 {
+        if d & 1 == 1 {
+            x *= q;
+            x %= n;
+        }
+        q *= q;
+        q %= n;
+        d >>= 1;
+    }
+    x as _
+}
+
+fn square(x: u64, n: u64) -> u64 {
+    let n: u128 = n.into();
+    let mut x: u128 = x.into();
+    x *= x;
+    x %= n;
+    x as _
+}
+
+fn is_prime(n: u64) -> bool {
+    const LOG_2_TO_E: [u64; 65] = [
+        0, 1, 2, 3, 3, 4, 5, 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 12, 13, 14, 14, 15, 16, 16, 17, 18,
+        19, 19, 20, 21, 21, 22, 23, 23, 24, 25, 25, 26, 27, 28, 28, 29, 30, 30, 31, 32, 32, 33, 34,
+        34, 35, 36, 37, 37, 38, 39, 39, 40, 41, 41, 42, 43, 43, 44, 45,
+    ];
+
+    match n {
+        0 => false,
+        1 => false,
+        2 => true,
+        3.. => {
+            let n1 = n - 1;
+            let s = n1.trailing_zeros();
+            let d = n1 >> s;
+            let log_e_approx = LOG_2_TO_E[(n.ilog2() + 1) as usize];
+            for a in 2..=(n - 2).min(2 * log_e_approx * log_e_approx) {
+                let mut x = pow(a, d, n);
+                for _ in 0..s {
+                    let y = square(x, n);
+                    if y == 1 && x != 1 && x != n1 {
+                        return false;
+                    }
+                    x = y;
+                }
+                if x != 1 {
+                    return false;
+                }
+            }
+            true
+        }
+    }
+}
+
+#[test]
+fn primes() {
+    assert!(!is_prime(0));
+    assert!(!is_prime(1));
+    assert!(is_prime(2));
+    assert!(is_prime(3));
+    assert!(!is_prime(4));
+    assert!(is_prime(5));
+    assert!(!is_prime(6));
+    assert!(is_prime(7));
+    assert!(!is_prime(8));
+    assert!(!is_prime(9));
+    assert!(!is_prime(10));
+    assert!(is_prime(11));
+    assert!(!is_prime(12));
+    assert!(is_prime(13));
+    assert!(!is_prime(14));
+    assert!(!is_prime(15));
+    assert!(!is_prime(16));
+    assert!(is_prime(17));
+    assert!(!is_prime(18));
+    assert!(is_prime(19));
+    assert!(!is_prime(20));
+    assert!(!is_prime(21));
+    assert!(!is_prime(22));
+    assert!(is_prime(23));
+    assert!(!is_prime(57));
+    assert!(is_prime(97));
+    assert!(is_prime(101));
+    assert!(is_prime(179));
+    assert!(!is_prime(216));
+    assert!(!is_prime(426));
+    assert!(is_prime(997));
+    assert!(is_prime(65537));
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+enum Method {
+    #[serde(rename = "isPrime")]
+    IsPrime,
+}
+
+#[derive(Debug, Deserialize)]
+struct Request {
+    method: Method,
+    number: Number,
+}
+
+#[derive(Debug, Serialize)]
+struct Response {
+    method: Method,
+    prime: bool,
+}
+
+fn json_prime(number: Number) -> bool {
+    match number {
+        Number::U64(n) => is_prime(n),
+        _ => false,
+    }
+}
+
+fn try_process(input: String) -> miniserde::Result<String> {
+    let Request {
+        method: Method::IsPrime,
+        number,
+    } = miniserde::json::from_str(&input)?;
+    let response = Response {
+        method: Method::IsPrime,
+        prime: json_prime(number),
+    };
+    Ok(miniserde::json::to_string(&response))
+}
+
+fn process(input: String) -> String {
+    try_process(input).unwrap_or_default()
+}
 
 async fn handle(stream: smol::io::Result<smol::net::TcpStream>) -> smol::io::Result<()> {
-    let (reader, mut writer) = stream?.split();
-    futures::io::copy(reader, &mut writer).await.map(|_| {})
+    let (reader, writer) = stream?.split();
+    let mut alive = true;
+    BufReader::new(reader)
+        .lines()
+        .map_ok(process)
+        .take_while(|item| {
+            ready(match item {
+                Ok(s) if s.is_empty() => std::mem::take(&mut alive),
+                _ => alive,
+            })
+        })
+        .map_ok(|s| s + "\n")
+        .forward(writer.into_sink::<String>())
+        .await
 }
 
 fn main() -> miette::Result<()> {