diff --git a/crates/oxc_language_server/src/backend.rs b/crates/oxc_language_server/src/backend.rs
index 83ab80f564e1d..d9aa42cc7a9b8 100644
--- a/crates/oxc_language_server/src/backend.rs
+++ b/crates/oxc_language_server/src/backend.rs
@@ -506,7 +506,8 @@ impl LanguageServer for Backend {
         // saving the file means we can read again from the file system
         self.file_system.write().await.remove(uri);
 
-        if let Some(diagnostics) = worker.run_diagnostic_on_save(uri, None).await {
+        if let Some(diagnostics) = worker.run_diagnostic_on_save(uri, params.text.as_deref()).await
+        {
             self.client.publish_diagnostics(uri.clone(), diagnostics, None).await;
         }
     }
diff --git a/crates/oxc_language_server/src/tests.rs b/crates/oxc_language_server/src/tests.rs
index 3cf519a89d265..e432a6a3b7ea9 100644
--- a/crates/oxc_language_server/src/tests.rs
+++ b/crates/oxc_language_server/src/tests.rs
@@ -148,6 +148,33 @@ impl Tool for FakeTool {
 
         vec![]
     }
+
+    fn run_diagnostic(&self, uri: &Uri, content: Option<&str>) -> Option<Vec<Diagnostic>> {
+        if uri.as_str().ends_with("diagnostics.config") {
+            return Some(vec![Diagnostic {
+                message: format!(
+                    "Fake diagnostic for content: {}",
+                    content.unwrap_or("<no content>")
+                ),
+                ..Default::default()
+            }]);
+        }
+        None
+    }
+
+    fn run_diagnostic_on_change(
+        &self,
+        uri: &Uri,
+        content: Option<&str>,
+    ) -> Option<Vec<Diagnostic>> {
+        // For this fake tool, we use the same logic as run_diagnostic
+        self.run_diagnostic(uri, content)
+    }
+
+    fn run_diagnostic_on_save(&self, uri: &Uri, content: Option<&str>) -> Option<Vec<Diagnostic>> {
+        // For this fake tool, we use the same logic as run_diagnostic
+        self.run_diagnostic(uri, content)
+    }
 }
 
 // A test server that can send requests and receive responses.
@@ -454,8 +481,8 @@ mod test_suite {
     use tower_lsp_server::{
         jsonrpc::{Id, Response},
         lsp_types::{
-            ApplyWorkspaceEditResponse, InitializeResult, ServerInfo, WorkspaceEdit,
-            WorkspaceFolder,
+            ApplyWorkspaceEditResponse, InitializeResult, PublishDiagnosticsParams, ServerInfo,
+            WorkspaceEdit, WorkspaceFolder,
         },
     };
 
@@ -989,4 +1016,95 @@ mod test_suite {
 
         server.shutdown(4).await;
     }
+
+    #[tokio::test]
+    async fn test_diagnostic_on_open() {
+        let mut server = TestServer::new_initialized(
+            |client| Backend::new(client, server_info(), vec![Box::new(FakeToolBuilder)]),
+            initialize_request(false, false, false),
+        )
+        .await;
+
+        let file = format!("{WORKSPACE}/diagnostics.config");
+        let content = "some text";
+        server.send_request(did_open(&file, content)).await;
+
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+        let params: PublishDiagnosticsParams =
+            serde_json::from_value(diagnostic_response.params().unwrap().clone()).unwrap();
+        assert_eq!(params.uri, file.parse().unwrap());
+        assert_eq!(params.diagnostics.len(), 1);
+        assert_eq!(
+            params.diagnostics[0].message,
+            format!("Fake diagnostic for content: {content}")
+        );
+
+        server.shutdown(4).await;
+    }
+
+    #[tokio::test]
+    async fn test_diagnostic_on_change() {
+        let mut server = TestServer::new_initialized(
+            |client| Backend::new(client, server_info(), vec![Box::new(FakeToolBuilder)]),
+            initialize_request(false, false, false),
+        )
+        .await;
+
+        let file = format!("{WORKSPACE}/diagnostics.config");
+        let content = "new text";
+        server.send_request(did_open(&file, "old text")).await;
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+
+        server.send_request(did_change(&file, content)).await;
+
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+        let params: PublishDiagnosticsParams =
+            serde_json::from_value(diagnostic_response.params().unwrap().clone()).unwrap();
+        assert_eq!(params.uri, file.parse().unwrap());
+        assert_eq!(params.diagnostics.len(), 1);
+        assert_eq!(
+            params.diagnostics[0].message,
+            format!("Fake diagnostic for content: {content}")
+        );
+
+        server.shutdown(4).await;
+    }
+
+    #[tokio::test]
+    async fn test_diagnostic_on_save() {
+        let mut server = TestServer::new_initialized(
+            |client| Backend::new(client, server_info(), vec![Box::new(FakeToolBuilder)]),
+            initialize_request(false, false, false),
+        )
+        .await;
+
+        let file = format!("{WORKSPACE}/diagnostics.config");
+        let content = "new text";
+        server.send_request(did_open(&file, "old text")).await;
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+
+        server.send_request(did_change(&file, content)).await;
+
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+
+        server.send_request(did_save(&file, content)).await;
+
+        let diagnostic_response = server.recv_notification().await;
+        assert_eq!(diagnostic_response.method(), "textDocument/publishDiagnostics");
+        let params: PublishDiagnosticsParams =
+            serde_json::from_value(diagnostic_response.params().unwrap().clone()).unwrap();
+        assert_eq!(params.uri, file.parse().unwrap());
+        assert_eq!(params.diagnostics.len(), 1);
+        assert_eq!(
+            params.diagnostics[0].message,
+            format!("Fake diagnostic for content: {content}")
+        );
+
+        server.shutdown(4).await;
+    }
 }
diff --git a/crates/oxc_language_server/src/worker.rs b/crates/oxc_language_server/src/worker.rs
index a77ef7e4e8544..6c9346cc30264 100644
--- a/crates/oxc_language_server/src/worker.rs
+++ b/crates/oxc_language_server/src/worker.rs
@@ -563,4 +563,123 @@ mod tests {
             panic!("Expected CodeAction");
         }
     }
+
+    #[tokio::test]
+    async fn test_run_diagnostic() {
+        let worker = WorkspaceWorker::new(Uri::from_str("file:///root/").unwrap());
+        let tools: Vec<Box<dyn ToolBuilder>> = vec![Box::new(FakeToolBuilder)];
+        worker.start_worker(serde_json::Value::Null, &tools).await;
+
+        let diagnostics_no_content = worker
+            .run_diagnostic(&Uri::from_str("file:///root/diagnostics.config").unwrap(), None)
+            .await;
+
+        assert!(diagnostics_no_content.is_some());
+        assert_eq!(diagnostics_no_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_no_content.unwrap()[0].message,
+            "Fake diagnostic for content: <no content>"
+        );
+
+        let diagnostics_with_content = worker
+            .run_diagnostic(
+                &Uri::from_str("file:///root/diagnostics.config").unwrap(),
+                Some("helloworld"),
+            )
+            .await;
+
+        assert!(diagnostics_with_content.is_some());
+        assert_eq!(diagnostics_with_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_with_content.unwrap()[0].message,
+            "Fake diagnostic for content: helloworld"
+        );
+
+        let no_diagnostics =
+            worker.run_diagnostic(&Uri::from_str("file:///root/unknown.file").unwrap(), None).await;
+
+        assert!(no_diagnostics.is_none());
+    }
+
+    #[tokio::test]
+    async fn test_run_diagnostic_on_change() {
+        let worker = WorkspaceWorker::new(Uri::from_str("file:///root/").unwrap());
+        let tools: Vec<Box<dyn ToolBuilder>> = vec![Box::new(FakeToolBuilder)];
+        worker.start_worker(serde_json::Value::Null, &tools).await;
+
+        let diagnostics_no_content = worker
+            .run_diagnostic_on_change(
+                &Uri::from_str("file:///root/diagnostics.config").unwrap(),
+                None,
+            )
+            .await;
+
+        assert!(diagnostics_no_content.is_some());
+        assert_eq!(diagnostics_no_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_no_content.unwrap()[0].message,
+            "Fake diagnostic for content: <no content>"
+        );
+
+        let diagnostics_with_content = worker
+            .run_diagnostic_on_change(
+                &Uri::from_str("file:///root/diagnostics.config").unwrap(),
+                Some("helloworld"),
+            )
+            .await;
+
+        assert!(diagnostics_with_content.is_some());
+        assert_eq!(diagnostics_with_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_with_content.unwrap()[0].message,
+            "Fake diagnostic for content: helloworld"
+        );
+
+        let no_diagnostics = worker
+            .run_diagnostic_on_change(&Uri::from_str("file:///root/unknown.file").unwrap(), None)
+            .await;
+
+        assert!(no_diagnostics.is_none());
+    }
+
+    #[tokio::test]
+    async fn test_run_diagnostic_on_save() {
+        let worker = WorkspaceWorker::new(Uri::from_str("file:///root/").unwrap());
+        let tools: Vec<Box<dyn ToolBuilder>> = vec![Box::new(FakeToolBuilder)];
+        worker.start_worker(serde_json::Value::Null, &tools).await;
+
+        let diagnostics_no_content = worker
+            .run_diagnostic_on_save(
+                &Uri::from_str("file:///root/diagnostics.config").unwrap(),
+                None,
+            )
+            .await;
+
+        assert!(diagnostics_no_content.is_some());
+        assert_eq!(diagnostics_no_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_no_content.unwrap()[0].message,
+            "Fake diagnostic for content: <no content>"
+        );
+
+        let diagnostics_with_content = worker
+            .run_diagnostic_on_save(
+                &Uri::from_str("file:///root/diagnostics.config").unwrap(),
+                Some("helloworld"),
+            )
+            .await;
+
+        assert!(diagnostics_with_content.is_some());
+        assert_eq!(diagnostics_with_content.as_ref().unwrap().len(), 1);
+        assert_eq!(
+            diagnostics_with_content.unwrap()[0].message,
+            "Fake diagnostic for content: helloworld"
+        );
+
+        let no_diagnostics = worker
+            .run_diagnostic_on_save(&Uri::from_str("file:///root/unknown.file").unwrap(), None)
+            .await;
+
+        assert!(no_diagnostics.is_none());
+    }
 }