diff --git a/blah-types/src/msg.rs b/blah-types/src/msg.rs
index c172639..3e1394c 100644
--- a/blah-types/src/msg.rs
+++ b/blah-types/src/msg.rs
@@ -1,5 +1,7 @@
 //! Core message subtypes.
 use std::fmt;
+use std::num::ParseIntError;
+use std::str::FromStr;
 
 use bitflags_serde_shim::impl_serde_for_bitflags;
 use serde::{de, ser, Deserialize, Serialize};
@@ -22,6 +24,14 @@ impl fmt::Display for Id {
     }
 }
 
+impl FromStr for Id {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        i64::from_str(s).map(Self)
+    }
+}
+
 impl Id {
     pub const MIN: Self = Id(i64::MIN);
     pub const MAX: Self = Id(i64::MAX);
diff --git a/blahd/src/lib.rs b/blahd/src/lib.rs
index f968792..7b22884 100644
--- a/blahd/src/lib.rs
+++ b/blahd/src/lib.rs
@@ -23,7 +23,7 @@ use blah_types::{get_timestamp, Id, Signed, UserKey};
 use database::{Transaction, TransactionOps};
 use feed::FeedData;
 use id::IdExt;
-use middleware::{Auth, MaybeAuth, ResultExt as _, SignedJson};
+use middleware::{Auth, ETag, MaybeAuth, ResultExt as _, SignedJson};
 use parking_lot::Mutex;
 use serde::{Deserialize, Deserializer, Serialize};
 use serde_inline_default::serde_inline_default;
@@ -434,11 +434,11 @@ async fn room_get_metadata(
 
 async fn room_get_feed<FT: feed::FeedType>(
     st: ArcState,
+    ETag(etag): ETag<Id>,
     R(OriginalUri(req_uri), _): RE<OriginalUri>,
     R(Path(rid), _): RE<Path<Id>>,
     R(Query(mut pagination), _): RE<Query<Pagination>>,
 ) -> Result<Response, ApiError> {
-    // TODO: If-None-Match.
     let self_url = st
         .config
         .base_url
@@ -460,6 +460,12 @@ async fn room_get_feed<FT: feed::FeedType>(
         Ok((title, msgs, skip_token))
     })?;
 
+    // Use `Id(0)` as the tag for an empty list.
+    let ret_etag = msgs.first().map_or(Id(0), |msg| msg.cid);
+    if etag == Some(ret_etag) {
+        return Ok(StatusCode::NOT_MODIFIED.into_response());
+    }
+
     let next_url = skip_token.map(|skip_token| {
         let next_params = Pagination {
             skip_token: Some(skip_token),
@@ -478,13 +484,14 @@ async fn room_get_feed<FT: feed::FeedType>(
         next_url
     });
 
-    Ok(FT::to_feed_response(FeedData {
+    let resp = FT::to_feed_response(FeedData {
         rid,
         title,
         msgs,
         self_url,
         next_url,
-    }))
+    });
+    Ok((ETag(Some(ret_etag)), resp).into_response())
 }
 
 /// Get room messages with pagination parameters,
diff --git a/blahd/src/middleware.rs b/blahd/src/middleware.rs
index 0faa5e5..9461071 100644
--- a/blahd/src/middleware.rs
+++ b/blahd/src/middleware.rs
@@ -1,12 +1,13 @@
 use std::backtrace::Backtrace;
 use std::convert::Infallible;
 use std::fmt;
+use std::str::FromStr;
 use std::sync::Arc;
 
 use axum::extract::rejection::{JsonRejection, PathRejection, QueryRejection};
 use axum::extract::{FromRef, FromRequest, FromRequestParts, Request};
-use axum::http::{header, request, StatusCode};
-use axum::response::{IntoResponse, Response};
+use axum::http::{header, request, HeaderValue, StatusCode};
+use axum::response::{IntoResponse, IntoResponseParts, Response, ResponseParts};
 use axum::{async_trait, Json};
 use blah_types::msg::AuthPayload;
 use blah_types::{Signed, UserKey};
@@ -244,3 +245,42 @@ where
         Ok(Self(data.signee.user))
     }
 }
+
+#[derive(Debug, Clone)]
+pub struct ETag<T>(pub Option<T>);
+
+#[async_trait]
+impl<S, T: FromStr> FromRequestParts<S> for ETag<T>
+where
+    S: Send + Sync,
+{
+    type Rejection = Infallible;
+
+    async fn from_request_parts(
+        parts: &mut request::Parts,
+        _state: &S,
+    ) -> Result<Self, Self::Rejection> {
+        let tag = parts
+            .headers
+            .get(header::IF_NONE_MATCH)
+            .and_then(|v| v.to_str().ok()?.strip_prefix('"')?.strip_suffix('"'))
+            .filter(|s| !s.is_empty())
+            .and_then(|s| s.parse::<T>().ok());
+        Ok(Self(tag))
+    }
+}
+
+impl<T: fmt::Display> IntoResponseParts for ETag<T> {
+    type Error = Infallible;
+
+    fn into_response_parts(self, mut res: ResponseParts) -> Result<ResponseParts, Self::Error> {
+        if let Some(tag) = &self.0 {
+            res.headers_mut().insert(
+                header::ETAG,
+                HeaderValue::from_str(&format!("\"{tag}\""))
+                    .expect("ETag must be a valid header value"),
+            );
+        }
+        Ok(res)
+    }
+}
diff --git a/blahd/tests/webapi.rs b/blahd/tests/webapi.rs
index 166d157..c693582 100644
--- a/blahd/tests/webapi.rs
+++ b/blahd/tests/webapi.rs
@@ -790,15 +790,60 @@ async fn room_feed(server: Server, #[case] typ: &'static str) {
         .join_room(rid, &BOB, MemberPermission::POST_CHAT)
         .await
         .unwrap();
-    server.post_chat(rid, &ALICE, "a").await.unwrap();
+    let feed_url = server.url(format!("/room/{rid}/feed.{typ}"));
+    let get_feed = |etag: Option<&str>| {
+        let mut req = server.client.get(&feed_url);
+        if let Some(etag) = etag {
+            req = req.header(header::IF_NONE_MATCH, etag);
+        }
+        async move {
+            let resp = req.send().await.unwrap().error_for_status().unwrap();
+            if resp.status() == StatusCode::NOT_MODIFIED {
+                None
+            } else {
+                let etag = resp.headers()[header::ETAG].to_str().unwrap().to_owned();
+                Some((etag, resp.text().await.unwrap()))
+            }
+        }
+    };
+
+    // Empty yet.
+    let etag_zero = "\"0\"";
+    assert_eq!(get_feed(None).await.unwrap().0, etag_zero);
+    // ETag should track from empty -> empty.
+    assert_eq!(get_feed(Some(etag_zero)).await, None);
+
+    // Post some chats.
+    let cid1 = server.post_chat(rid, &ALICE, "a").await.unwrap().cid;
+    // Got some response.
+    let etag_one = format!("\"{cid1}\"");
+    {
+        let resp1 = get_feed(None).await.unwrap();
+        // ETag should track from empty -> non-empty.
+        let resp2 = get_feed(Some(etag_zero)).await.unwrap();
+        // Idempotent.
+        assert_eq!(resp1, resp2);
+        assert_eq!(resp1.0, etag_one);
+    }
+
+    // Post more chats.
     let cid2 = server.post_chat(rid, &BOB, "b1").await.unwrap().cid;
-    server.post_chat(rid, &BOB, "b2").await.unwrap();
+    let cid3 = server.post_chat(rid, &BOB, "b2").await.unwrap().cid;
+
+    let etag_last = format!("\"{cid3}\"");
+    let resp = {
+        let resp1 = get_feed(None).await.unwrap();
+        // ETag should track from non-empty -> non-empty.
+        let resp2 = get_feed(Some(&etag_one)).await.unwrap();
+        // Idempotent.
+        assert_eq!(resp1, resp2);
+        assert_eq!(resp1.0, etag_last);
+        assert_eq!(get_feed(Some(&etag_last)).await, None);
+        resp1.1
+    };
 
     if typ == "json" {
-        let feed = server
-            .get::<serde_json::Value>(&format!("/room/{rid}/feed.json"), None)
-            .await
-            .unwrap();
+        let feed = serde_json::from_str::<serde_json::Value>(&resp).unwrap();
         // TODO: Ideally we should assert on the result, but it contains time and random id currently.
         assert_eq!(feed["title"].as_str().unwrap(), "public");
         assert_eq!(feed["items"].as_array().unwrap().len(), 2);
@@ -820,17 +865,6 @@ async fn room_feed(server: Server, #[case] typ: &'static str) {
         assert_eq!(items.len(), 1);
         assert_eq!(items[0]["content_html"].as_str().unwrap(), "a");
     } else {
-        let resp = server
-            .client
-            .get(server.url(format!("/room/{rid}/feed.atom")))
-            .send()
-            .await
-            .unwrap()
-            .error_for_status()
-            .unwrap()
-            .text()
-            .await
-            .unwrap();
         assert!(resp.starts_with(r#"<?xml version="1.0" encoding="utf-8"?>"#));
         assert_eq!(resp.matches("<entry>").count(), 2);
     }