diff --git a/tests/server/datastar.rs b/tests/server/datastar.rs
new file mode 100644
index 0000000..e1aace5
--- /dev/null
+++ b/tests/server/datastar.rs
@@ -0,0 +1,513 @@
+//! Integration tests for Datastar partial rendering.
+//!
+//! These tests verify that endpoints return HTML fragments with correct
+//! Datastar headers when the `datastar-request: true` header is present.
+
+use crate::helpers::{
+    assert_datastar_headers, assert_full_page, assert_html_fragment, create_default_bag,
+    create_default_roast, create_default_roaster, spawn_app_with_auth,
+};
+use brewlog::domain::bags::UpdateBag;
+use brewlog::domain::roasters::NewRoaster;
+use brewlog::domain::roasts::NewRoast;
+use reqwest::Client;
+
+// ============================================================================
+// Roasters
+// ============================================================================
+
+#[tokio::test]
+async fn roasters_list_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    create_default_roaster(&app).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/roasters", app.address))
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to fetch roasters");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roaster-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+    assert!(
+        body.contains("id=\"roaster-list\""),
+        "Fragment should contain the selector element"
+    );
+}
+
+#[tokio::test]
+async fn roasters_list_without_datastar_header_returns_full_page() {
+    let app = spawn_app_with_auth().await;
+    create_default_roaster(&app).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/roasters", app.address))
+        .send()
+        .await
+        .expect("failed to fetch roasters");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let body = response.text().await.expect("failed to read body");
+    assert_full_page(&body);
+}
+
+#[tokio::test]
+async fn roasters_create_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let client = Client::new();
+
+    let new_roaster = NewRoaster {
+        name: "Datastar Test Roasters".to_string(),
+        country: "UK".to_string(),
+        city: None,
+        homepage: None,
+        notes: None,
+    };
+
+    let response = client
+        .post(app.api_url("/roasters"))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .json(&new_roaster)
+        .send()
+        .await
+        .expect("failed to create roaster");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roaster-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+    assert!(
+        body.contains("Datastar Test Roasters"),
+        "Fragment should include created roaster"
+    );
+}
+
+#[tokio::test]
+async fn roasters_create_without_datastar_header_returns_json() {
+    let app = spawn_app_with_auth().await;
+    let client = Client::new();
+
+    let new_roaster = NewRoaster {
+        name: "JSON Test Roasters".to_string(),
+        country: "UK".to_string(),
+        city: None,
+        homepage: None,
+        notes: None,
+    };
+
+    let response = client
+        .post(app.api_url("/roasters"))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .json(&new_roaster)
+        .send()
+        .await
+        .expect("failed to create roaster");
+
+    assert_eq!(response.status(), 201);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let roaster: brewlog::domain::roasters::Roaster =
+        response.json().await.expect("failed to parse JSON");
+    assert_eq!(roaster.name, "JSON Test Roasters");
+}
+
+#[tokio::test]
+async fn roasters_delete_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let client = Client::new();
+
+    let response = client
+        .delete(app.api_url(&format!("/roasters/{}", roaster.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to delete roaster");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roaster-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn roasters_delete_without_datastar_header_returns_204() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let client = Client::new();
+
+    let response = client
+        .delete(app.api_url(&format!("/roasters/{}", roaster.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .send()
+        .await
+        .expect("failed to delete roaster");
+
+    assert_eq!(response.status(), 204);
+    assert!(response.headers().get("datastar-selector").is_none());
+}
+
+// ============================================================================
+// Roasts
+// ============================================================================
+
+#[tokio::test]
+async fn roasts_list_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/roasts", app.address))
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to fetch roasts");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roast-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+    assert!(
+        body.contains("id=\"roast-list\""),
+        "Fragment should contain the selector element"
+    );
+}
+
+#[tokio::test]
+async fn roasts_list_without_datastar_header_returns_full_page() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/roasts", app.address))
+        .send()
+        .await
+        .expect("failed to fetch roasts");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let body = response.text().await.expect("failed to read body");
+    assert_full_page(&body);
+}
+
+#[tokio::test]
+async fn roasts_create_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let client = Client::new();
+
+    let new_roast = NewRoast {
+        roaster_id: roaster.id,
+        name: "Datastar Roast".to_string(),
+        origin: "Ethiopia".to_string(),
+        region: "Yirgacheffe".to_string(),
+        producer: "Test Farm".to_string(),
+        tasting_notes: vec!["Blueberry".to_string()],
+        process: "Washed".to_string(),
+    };
+
+    let response = client
+        .post(app.api_url("/roasts"))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .json(&new_roast)
+        .send()
+        .await
+        .expect("failed to create roast");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roast-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+    assert!(
+        body.contains("Datastar Roast"),
+        "Fragment should include created roast"
+    );
+}
+
+#[tokio::test]
+async fn roasts_delete_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let response = client
+        .delete(app.api_url(&format!("/roasts/{}", roast.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to delete roast");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roast-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn roast_options_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(app.api_url(&format!("/roasts?roaster_id={}", roaster.id)))
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to fetch roast options");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#roast-select-options");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn roast_options_without_datastar_header_returns_json() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(app.api_url(&format!("/roasts?roaster_id={}", roaster.id)))
+        .send()
+        .await
+        .expect("failed to fetch roast options");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let roasts: Vec<brewlog::domain::roasts::RoastWithRoaster> =
+        response.json().await.expect("failed to parse JSON");
+    assert_eq!(roasts.len(), 1);
+}
+
+// ============================================================================
+// Bags
+// ============================================================================
+
+#[tokio::test]
+async fn bags_list_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    create_default_bag(&app, roast.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/bags", app.address))
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to fetch bags");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#bag-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+    assert!(
+        body.contains("id=\"bag-list\""),
+        "Fragment should contain the selector element"
+    );
+}
+
+#[tokio::test]
+async fn bags_list_without_datastar_header_returns_full_page() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    create_default_bag(&app, roast.id).await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/bags", app.address))
+        .send()
+        .await
+        .expect("failed to fetch bags");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let body = response.text().await.expect("failed to read body");
+    assert_full_page(&body);
+}
+
+#[tokio::test]
+async fn bags_create_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    let client = Client::new();
+
+    let new_bag = serde_json::json!({
+        "roast_id": roast.id,
+        "roast_date": "2023-06-15",
+        "amount": 350.0
+    });
+
+    let response = client
+        .post(app.api_url("/bags"))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .json(&new_bag)
+        .send()
+        .await
+        .expect("failed to create bag");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#bag-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn bags_update_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    let bag = create_default_bag(&app, roast.id).await;
+    let client = Client::new();
+
+    let update = UpdateBag {
+        remaining: Some(100.0),
+        closed: None,
+        finished_at: None,
+    };
+
+    let response = client
+        .put(app.api_url(&format!("/bags/{}", bag.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .json(&update)
+        .send()
+        .await
+        .expect("failed to update bag");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#bag-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn bags_update_without_datastar_header_returns_json() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    let bag = create_default_bag(&app, roast.id).await;
+    let client = Client::new();
+
+    let update = UpdateBag {
+        remaining: Some(100.0),
+        closed: None,
+        finished_at: None,
+    };
+
+    let response = client
+        .put(app.api_url(&format!("/bags/{}", bag.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .json(&update)
+        .send()
+        .await
+        .expect("failed to update bag");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let updated_bag: brewlog::domain::bags::Bag =
+        response.json().await.expect("failed to parse JSON");
+    assert_eq!(updated_bag.remaining, 100.0);
+}
+
+#[tokio::test]
+async fn bags_delete_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let roaster = create_default_roaster(&app).await;
+    let roast = create_default_roast(&app, roaster.id).await;
+    let bag = create_default_bag(&app, roast.id).await;
+    let client = Client::new();
+
+    let response = client
+        .delete(app.api_url(&format!("/bags/{}", bag.id)))
+        .bearer_auth(app.auth_token.as_ref().unwrap())
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to delete bag");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#bag-list");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+// ============================================================================
+// Timeline
+// ============================================================================
+
+#[tokio::test]
+async fn timeline_with_datastar_header_returns_fragment() {
+    let app = spawn_app_with_auth().await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/timeline", app.address))
+        .header("datastar-request", "true")
+        .send()
+        .await
+        .expect("failed to fetch timeline");
+
+    assert_eq!(response.status(), 200);
+    assert_datastar_headers(&response, "#timeline-loader");
+
+    let body = response.text().await.expect("failed to read body");
+    assert_html_fragment(&body);
+}
+
+#[tokio::test]
+async fn timeline_without_datastar_header_returns_full_page() {
+    let app = spawn_app_with_auth().await;
+    let client = Client::new();
+
+    let response = client
+        .get(format!("{}/timeline", app.address))
+        .send()
+        .await
+        .expect("failed to fetch timeline");
+
+    assert_eq!(response.status(), 200);
+    assert!(response.headers().get("datastar-selector").is_none());
+
+    let body = response.text().await.expect("failed to read body");
+    assert_full_page(&body);
+}
diff --git a/tests/server/helpers.rs b/tests/server/helpers.rs
index 6b03b3a..0011f95 100644
--- a/tests/server/helpers.rs
+++ b/tests/server/helpers.rs
@@ -215,3 +215,74 @@ pub async fn create_roaster_with_name(app: &TestApp, name: &str) -> Roaster {
     )
     .await
 }
+
+pub async fn create_default_bag(
+    app: &TestApp,
+    roast_id: brewlog::domain::ids::RoastId,
+) -> brewlog::domain::bags::Bag {
+    let client = Client::new();
+    let new_bag = brewlog::domain::bags::NewBag {
+        roast_id,
+        roast_date: Some(chrono::NaiveDate::from_ymd_opt(2023, 1, 1).unwrap()),
+        amount: 250.0,
+    };
+
+    let mut request = client.post(app.api_url("/bags")).json(&new_bag);
+
+    if let Some(token) = &app.auth_token {
+        request = request.bearer_auth(token);
+    }
+
+    let response = request.send().await.expect("failed to create bag via API");
+
+    response
+        .json()
+        .await
+        .expect("failed to deserialize bag from response")
+}
+
+/// Asserts that the response has valid Datastar fragment headers
+pub fn assert_datastar_headers(response: &reqwest::Response, expected_selector: &str) {
+    let selector = response
+        .headers()
+        .get("datastar-selector")
+        .and_then(|v| v.to_str().ok());
+    assert_eq!(
+        selector,
+        Some(expected_selector),
+        "Expected datastar-selector header to be '{}', got {:?}",
+        expected_selector,
+        selector
+    );
+
+    let mode = response
+        .headers()
+        .get("datastar-mode")
+        .and_then(|v| v.to_str().ok());
+    assert_eq!(
+        mode,
+        Some("replace"),
+        "Expected datastar-mode header to be 'replace', got {:?}",
+        mode
+    );
+}
+
+/// Asserts that the response body is an HTML fragment (not a full page)
+pub fn assert_html_fragment(body: &str) {
+    assert!(
+        !body.contains("<!DOCTYPE"),
+        "Expected HTML fragment, but found DOCTYPE declaration"
+    );
+    assert!(
+        !body.contains("<html"),
+        "Expected HTML fragment, but found <html> tag"
+    );
+}
+
+/// Asserts that the body contains full HTML page structure
+pub fn assert_full_page(body: &str) {
+    assert!(
+        body.contains("<!DOCTYPE") || body.contains("<html"),
+        "Expected full HTML page with DOCTYPE or <html> tag"
+    );
+}
diff --git a/tests/server/main.rs b/tests/server/main.rs
index 1aa4fd3..5869d92 100644
--- a/tests/server/main.rs
+++ b/tests/server/main.rs
@@ -1,5 +1,6 @@
 pub mod auth_api;
 pub mod bags_api;
+pub mod datastar;
 pub mod helpers;
 pub mod roasters_api;
 pub mod roasts_api;