diff --git a/Cargo.lock b/Cargo.lock
index ad74e4df..1719c394 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -170,6 +170,12 @@ dependencies = [
  "syn 2.0.53",
 ]
 
+[[package]]
+name = "auto-future"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c1e7e457ea78e524f48639f551fd79703ac3f2237f5ecccdf4708f8a75ad373"
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
@@ -217,7 +223,7 @@ dependencies = [
  "http 1.1.0",
  "http-body 1.0.0",
  "http-body-util",
- "hyper 1.2.0",
+ "hyper 1.3.1",
  "hyper-util",
  "itoa",
  "matchit",
@@ -298,6 +304,35 @@ dependencies = [
  "tower-http",
 ]
 
+[[package]]
+name = "axum-test"
+version = "14.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c5dd01c3ff7d926efc6db38bc9a2a5fe82ebe3bf85e44200a7ae3b6bda5f4e5"
+dependencies = [
+ "anyhow",
+ "async-trait",
+ "auto-future",
+ "axum 0.7.5",
+ "bytes",
+ "cookie",
+ "http 1.1.0",
+ "http-body-util",
+ "hyper 1.3.1",
+ "hyper-util",
+ "mime",
+ "pretty_assertions",
+ "reserve-port",
+ "rust-multipart-rfc7578_2",
+ "serde",
+ "serde_json",
+ "serde_urlencoded",
+ "smallvec",
+ "tokio",
+ "tower",
+ "url",
+]
+
 [[package]]
 name = "backtrace"
 version = "0.3.70"
@@ -340,7 +375,7 @@ dependencies = [
  "bitflags 2.5.0",
  "cexpr",
  "clang-sys",
- "itertools 0.11.0",
+ "itertools 0.12.1",
  "lazy_static",
  "lazycell",
  "log",
@@ -453,9 +488,9 @@ checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
 
 [[package]]
 name = "bytes"
-version = "1.5.0"
+version = "1.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a2bd12c1caf447e69cd4528f47f94d203fd2582878ecb9e9465484c4148a8223"
+checksum = "514de17de45fdb8dc022b1a7975556c53c86f9f0aa5f534b98977b171857c2c9"
 
 [[package]]
 name = "cast"
@@ -493,6 +528,7 @@ version = "0.7.8"
 dependencies = [
  "axum 0.7.5",
  "axum-prometheus",
+ "axum-test",
  "base64 0.22.1",
  "clap",
  "config",
@@ -708,6 +744,16 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "cookie"
+version = "0.18.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ddef33a339a91ea89fb53151bd0a4689cfce27055c291dfa69945475d22c747"
+dependencies = [
+ "time",
+ "version_check",
+]
+
 [[package]]
 name = "core-foundation"
 version = "0.9.4"
@@ -953,6 +999,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "diff"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -980,15 +1032,15 @@ checksum = "1435fa1053d8b2fbbe9be7e97eca7f33d37b28409959813daefc1446a14247f1"
 
 [[package]]
 name = "duration-str"
-version = "0.7.1"
+version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a8bb6a301a95ba86fa0ebaf71d49ae4838c51f8b84cb88ed140dfb66452bb3c4"
+checksum = "7c1a2e028bbf7921549873b291ddc0cfe08b673d9489da81ac28898cd5a0e6e0"
 dependencies = [
- "nom",
  "rust_decimal",
  "serde",
  "thiserror",
  "time",
+ "winnow 0.6.8",
 ]
 
 [[package]]
@@ -1509,9 +1561,9 @@ dependencies = [
 
 [[package]]
 name = "hyper"
-version = "1.2.0"
+version = "1.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "186548d73ac615b32a73aafe38fb4f56c0d340e110e5a200bcadbaf2e199263a"
+checksum = "fe575dd17d0862a9a33781c8c4696a55c320909004a67a00fb286ba8b1bc496d"
 dependencies = [
  "bytes",
  "futures-channel",
@@ -1548,7 +1600,7 @@ checksum = "70206fc6890eaca9fde8a0bf71caa2ddfc9fe045ac9e5c70df101a7dbde866e0"
 dependencies = [
  "bytes",
  "http-body-util",
- "hyper 1.2.0",
+ "hyper 1.3.1",
  "hyper-util",
  "native-tls",
  "tokio",
@@ -1567,7 +1619,7 @@ dependencies = [
  "futures-util",
  "http 1.1.0",
  "http-body 1.0.0",
- "hyper 1.2.0",
+ "hyper 1.3.1",
  "pin-project-lite",
  "socket2",
  "tokio",
@@ -1740,6 +1792,15 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba291022dbbd398a455acf126c1e341954079855bc60dfdda641363bd6922569"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itertools"
 version = "0.13.0"
@@ -1915,6 +1976,16 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "mime_guess"
+version = "2.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4192263c238a5f0d0c6bfd21f336a313a4ce1c450542449ca191bb657b4642ef"
+dependencies = [
+ "mime",
+ "unicase",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -2530,6 +2601,16 @@ dependencies = [
  "termtree",
 ]
 
+[[package]]
+name = "pretty_assertions"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af7cee1a6c8a5b9208b3cb1061f10c0cb689087b3d8ce85fb9d2dd7a29b6ba66"
+dependencies = [
+ "diff",
+ "yansi",
+]
+
 [[package]]
 name = "prettyplease"
 version = "0.2.16"
@@ -2646,7 +2727,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "81bddcdb20abf9501610992b6759a4c888aef7d1a7247ef75e2404275ac24af1"
 dependencies = [
  "anyhow",
- "itertools 0.11.0",
+ "itertools 0.12.1",
  "proc-macro2",
  "quote",
  "syn 2.0.53",
@@ -2890,7 +2971,7 @@ dependencies = [
  "http 1.1.0",
  "http-body 1.0.0",
  "http-body-util",
- "hyper 1.2.0",
+ "hyper 1.3.1",
  "hyper-tls",
  "hyper-util",
  "ipnet",
@@ -2917,6 +2998,16 @@ dependencies = [
  "winreg",
 ]
 
+[[package]]
+name = "reserve-port"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9838134a2bfaa8e1f40738fcc972ac799de6e0e06b5157acb95fc2b05a0ea283"
+dependencies = [
+ "lazy_static",
+ "thiserror",
+]
+
 [[package]]
 name = "rgb"
 version = "0.8.37"
@@ -2992,6 +3083,22 @@ dependencies = [
  "ordered-multimap",
 ]
 
+[[package]]
+name = "rust-multipart-rfc7578_2"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "03b748410c0afdef2ebbe3685a6a862e2ee937127cdaae623336a459451c8d57"
+dependencies = [
+ "bytes",
+ "futures-core",
+ "futures-util",
+ "http 0.2.12",
+ "mime",
+ "mime_guess",
+ "rand",
+ "thiserror",
+]
+
 [[package]]
 name = "rust_decimal"
 version = "1.34.3"
@@ -3786,7 +3893,7 @@ dependencies = [
  "serde",
  "serde_spanned",
  "toml_datetime",
- "winnow 0.6.5",
+ "winnow 0.6.8",
 ]
 
 [[package]]
@@ -3978,6 +4085,15 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
 
+[[package]]
+name = "unicase"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7d2d4dafb69621809a81864c9c1b864479e1235c0dd4e199924b9742439ed89"
+dependencies = [
+ "version_check",
+]
+
 [[package]]
 name = "unicode-bidi"
 version = "0.3.15"
@@ -4427,9 +4543,9 @@ dependencies = [
 
 [[package]]
 name = "winnow"
-version = "0.6.5"
+version = "0.6.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dffa400e67ed5a4dd237983829e66475f0a4a26938c4b04c21baede6262215b8"
+checksum = "c3c52e9c97a68071b23e836c9380edae937f17b9c4667bd021973efc689f618d"
 dependencies = [
  "memchr",
 ]
@@ -4462,6 +4578,12 @@ dependencies = [
  "linked-hash-map",
 ]
 
+[[package]]
+name = "yansi"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09041cd90cf85f7f8b2df60c646f853b7f535ce68f85244eb6731cf89fa498ec"
+
 [[package]]
 name = "yasna"
 version = "0.5.2"
diff --git a/certifier/Cargo.toml b/certifier/Cargo.toml
index 180f1c7e..24bca737 100644
--- a/certifier/Cargo.toml
+++ b/certifier/Cargo.toml
@@ -26,8 +26,8 @@ rand = "0.8.5"
 serde_json = "1.0.117"
 base64 = "0.22.1"
 axum-prometheus = "0.6.1"
-tower = { version = "0.4.13", features = ["limit"] }
-duration-str = { version = "0.7.1", default-features = false, features = [
+tower = { version = "0.4.13", features = ["limit", "load-shed", "buffer"] }
+duration-str = { version = "0.10.0", default-features = false, features = [
     "serde",
     "time",
 ] }
@@ -35,5 +35,6 @@ parity-scale-codec = { version = "3.6.12", features = ["derive", "serde"] }
 mockall = "0.12.1"
 
 [dev-dependencies]
+axum-test = "14.9.1"
 reqwest = { version = "0.12.4", features = ["json"] }
 tempfile = "3.8.1"
diff --git a/certifier/README.md b/certifier/README.md
index 5ba4539f..4e146535 100644
--- a/certifier/README.md
+++ b/certifier/README.md
@@ -45,6 +45,15 @@ init_cfg:
 
 metrics: "127.0.0.1:9090"
 randomx_mode: Fast
+
+limits:
+  # How many requests can be processed in parallel.
+  # As PoST verification is CPU-bound, it defaults to the number of CPUs.
+  max_concurrent_requests: 4
+  # How many requests can be queued, waiting to be processed.
+  max_pending_requests: 1000
+  # Maximum size of request body (the proof JSON)
+  max_body_size: 1024
 ```
 
 Each field can also be provided as env variable prefixed with CERTIFIER. For example, `CERTIFIER_SIGNING_KEY`.
diff --git a/certifier/src/certifier.rs b/certifier/src/certifier.rs
index 6b132385..f93b05b4 100644
--- a/certifier/src/certifier.rs
+++ b/certifier/src/certifier.rs
@@ -1,7 +1,11 @@
 use std::sync::Arc;
 use std::time::{Duration, SystemTime};
 
+use axum::error_handling::HandleErrorLayer;
+use axum::extract::DefaultBodyLimit;
 use axum::http::StatusCode;
+use axum::response::{IntoResponse, Response};
+use axum::BoxError;
 use axum::{extract::State, Json};
 use axum::{routing::post, Router};
 use ed25519_dalek::{Signature, Signer, SigningKey};
@@ -11,9 +15,14 @@ use post::pow::randomx::PoW;
 use post::verification::Mode;
 use serde::{Deserialize, Serialize};
 use serde_with::{base64::Base64, serde_as};
+use tower::buffer::BufferLayer;
+use tower::limit::ConcurrencyLimitLayer;
+use tower::load_shed::error::Overloaded;
+use tower::load_shed::LoadShedLayer;
+use tower::ServiceBuilder;
 use tracing::instrument;
 
-use crate::configuration::RandomXMode;
+use crate::configuration::{Limits, RandomXMode};
 use crate::time::unix_timestamp;
 
 #[derive(Debug, Deserialize, Serialize)]
@@ -161,6 +170,32 @@ pub fn new(
         .with_state(Arc::new(certifier))
 }
 
+pub trait RouterLimiter {
+    fn apply_limits(self, limits: Limits) -> Self;
+}
+
+impl RouterLimiter for Router {
+    fn apply_limits(self, limits: Limits) -> Self {
+        self.layer(
+            ServiceBuilder::new()
+                .layer(DefaultBodyLimit::max(limits.max_body_size))
+                .layer(HandleErrorLayer::new(handle_error))
+                .layer(LoadShedLayer::new())
+                .layer(BufferLayer::new(limits.max_pending_requests))
+                .layer(ConcurrencyLimitLayer::new(limits.max_concurrent_requests))
+                .into_inner(),
+        )
+    }
+}
+
+async fn handle_error(error: BoxError) -> Response {
+    if error.is::<Overloaded>() {
+        StatusCode::TOO_MANY_REQUESTS.into_response()
+    } else {
+        StatusCode::INTERNAL_SERVER_ERROR.into_response()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::{
@@ -168,13 +203,14 @@ mod tests {
         time::{Duration, SystemTime},
     };
 
-    use crate::time::unix_timestamp;
+    use crate::{certifier::RouterLimiter, configuration::Limits, time::unix_timestamp};
 
     use super::{Certificate, Certifier, MockVerifier};
+    use axum::{body::Bytes, routing::post, Router};
+    use axum_test::TestServer;
     use ed25519_dalek::SigningKey;
     use parity_scale_codec::Decode;
     use post::{metadata::ProofMetadata, prove::Proof};
-
     #[test]
     fn certify_invalid_post() {
         let mut verifier = MockVerifier::new();
@@ -259,4 +295,20 @@ mod tests {
         assert!(expiration >= unix_timestamp(started + expiry));
         assert!(expiration <= unix_timestamp(SystemTime::now() + expiry));
     }
+
+    #[tokio::test]
+    async fn limit_max_body_size() {
+        let my_app = Router::new()
+            .route("/", post(|_: Bytes| async {}))
+            .apply_limits(Limits {
+                max_concurrent_requests: 1,
+                max_pending_requests: 1,
+                max_body_size: 5,
+            });
+
+        let server = TestServer::new(my_app).unwrap();
+
+        let response = server.post("/").text("i'm a very long text").await;
+        assert_eq!(response.status_code(), 413);
+    }
 }
diff --git a/certifier/src/configuration.rs b/certifier/src/configuration.rs
index 6b17f0ac..b9a9a13a 100644
--- a/certifier/src/configuration.rs
+++ b/certifier/src/configuration.rs
@@ -39,10 +39,7 @@ pub struct Config {
     /// The address to listen on for incoming requests.
     pub listen: std::net::SocketAddr,
 
-    /// The maximum number of requests to process in parallel.
-    /// Typically set to the number of cores, which is the default (if not set).
-    #[serde(default = "max_concurrency")]
-    pub max_concurrent_requests: usize,
+    pub limits: Limits,
 
     #[serde_as(as = "Base64")]
     /// The base64-encoded secret key used to sign the proofs.
@@ -66,6 +63,26 @@ pub struct Config {
     pub metrics: Option<std::net::SocketAddr>,
 }
 
+#[derive(Debug, serde::Deserialize, Clone)]
+pub struct Limits {
+    /// The maximum number of requests to process in parallel.
+    /// Typically set to the number of cores, which is the default (if not set).
+    #[serde(default = "max_concurrency")]
+    pub max_concurrent_requests: usize,
+
+    /// The maximum number of requests to queue up before rejecting new requests.
+    /// Rejected requests have 429 TOO_MANY_REQUESTS status code.
+    pub max_pending_requests: usize,
+
+    /// The maximum size of a request body (the proof JSON)
+    #[serde(default = "default_max_body")]
+    pub max_body_size: usize,
+}
+
+fn default_max_body() -> usize {
+    1024
+}
+
 pub fn get_configuration(config_path: &Path) -> Result<Config, config::ConfigError> {
     info!("loading configuration from {config_path:?}");
 
diff --git a/certifier/src/main.rs b/certifier/src/main.rs
index 1e3f3463..72ab428d 100644
--- a/certifier/src/main.rs
+++ b/certifier/src/main.rs
@@ -3,10 +3,10 @@ use std::{future::IntoFuture, path::PathBuf};
 use axum::routing::get;
 use axum_prometheus::PrometheusMetricLayerBuilder;
 use base64::{engine::general_purpose, Engine as _};
+use certifier::certifier::RouterLimiter;
 use clap::{arg, Parser, Subcommand};
 use ed25519_dalek::SigningKey;
 use tokio::net::TcpListener;
-use tower::limit::ConcurrencyLimitLayer;
 use tracing::info;
 use tracing_log::LogTracer;
 use tracing_subscriber::{EnvFilter, FmtSubscriber};
@@ -77,10 +77,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     info!("POST proof configuration: {:?}", config.post_cfg);
     info!("POST init configuration: {:?}", config.init_cfg);
     info!("RandomX mode: {:?}", config.randomx_mode);
-    info!(
-        "max concurrent requests: {}",
-        config.max_concurrent_requests
-    );
+    info!("{:?}", config.limits);
     if let Some(expiry) = config.certificate_expiration {
         info!("generated certificates will expire after {expiry:?}");
     } else {
@@ -94,7 +91,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         config.randomx_mode,
         config.certificate_expiration,
     )
-    .layer(ConcurrencyLimitLayer::new(config.max_concurrent_requests));
+    .apply_limits(config.limits);
 
     if let Some(addr) = config.metrics {
         info!("metrics enabled on: http://{addr:?}/metrics");