diff --git a/cli/lsp/diagnostics.rs b/cli/lsp/diagnostics.rs
index 7ddb3ff7b4..47b26d92ea 100644
--- a/cli/lsp/diagnostics.rs
+++ b/cli/lsp/diagnostics.rs
@@ -444,13 +444,21 @@ async fn generate_deps_diagnostics(
                       range,
                       severity: Some(lsp::DiagnosticSeverity::Error),
                       code,
-                      code_description: None,
                       source: Some("deno".to_string()),
                       message,
-                      related_information: None,
-                      tags: None,
-                      data: None,
+                      ..Default::default()
                     });
+                  } else if sources.contains_key(&specifier) {
+                    if let Some(message) = sources.get_maybe_warning(&specifier) {
+                      diagnostics.push(lsp::Diagnostic {
+                        range,
+                        severity: Some(lsp::DiagnosticSeverity::Warning),
+                        code: Some(lsp::NumberOrString::String("deno-warn".to_string())),
+                        source: Some("deno".to_string()),
+                        message,
+                        ..Default::default()
+                      })
+                    }
                   }
                 },
               }
diff --git a/cli/lsp/sources.rs b/cli/lsp/sources.rs
index 5894e8d974..c5586a4401 100644
--- a/cli/lsp/sources.rs
+++ b/cli/lsp/sources.rs
@@ -14,11 +14,11 @@ use crate::module_graph::GraphBuilder;
 use crate::program_state::ProgramState;
 use crate::specifier_handler::FetchHandler;
 use crate::text_encoding;
-use deno_runtime::permissions::Permissions;
 
 use deno_core::error::AnyError;
 use deno_core::serde_json;
 use deno_core::ModuleSpecifier;
+use deno_runtime::permissions::Permissions;
 use std::collections::HashMap;
 use std::fs;
 use std::path::Path;
@@ -105,6 +105,7 @@ struct Metadata {
   length_utf16: usize,
   line_index: LineIndex,
   maybe_types: Option<analysis::ResolvedDependency>,
+  maybe_warning: Option<String>,
   media_type: MediaType,
   source: String,
   version: String,
@@ -116,6 +117,7 @@ impl Metadata {
     source: &str,
     version: &str,
     media_type: &MediaType,
+    maybe_warning: Option<String>,
     maybe_import_map: &Option<ImportMap>,
   ) -> Self {
     let (dependencies, maybe_types) = if let Ok(parsed_module) =
@@ -138,6 +140,7 @@ impl Metadata {
       length_utf16: source.encode_utf16().count(),
       line_index,
       maybe_types,
+      maybe_warning,
       media_type: media_type.to_owned(),
       source: source.to_string(),
       version: version.to_string(),
@@ -180,6 +183,13 @@ impl Sources {
     self.0.lock().unwrap().get_maybe_types(specifier)
   }
 
+  pub fn get_maybe_warning(
+    &self,
+    specifier: &ModuleSpecifier,
+  ) -> Option<String> {
+    self.0.lock().unwrap().get_maybe_warning(specifier)
+  }
+
   pub fn get_media_type(
     &self,
     specifier: &ModuleSpecifier,
@@ -271,6 +281,14 @@ impl Inner {
     metadata.maybe_types
   }
 
+  fn get_maybe_warning(
+    &mut self,
+    specifier: &ModuleSpecifier,
+  ) -> Option<String> {
+    let metadata = self.get_metadata(&specifier)?;
+    metadata.maybe_warning
+  }
+
   fn get_media_type(
     &mut self,
     specifier: &ModuleSpecifier,
@@ -292,11 +310,11 @@ impl Inner {
     let path = self.get_path(specifier)?;
     let bytes = fs::read(path).ok()?;
     let scheme = specifier.scheme();
-    let (source, media_type, maybe_types) = if scheme == "file" {
+    let (source, media_type, maybe_types, maybe_warning) = if scheme == "file" {
       let maybe_charset =
         Some(text_encoding::detect_charset(&bytes).to_string());
       let source = get_source_from_bytes(bytes, maybe_charset).ok()?;
-      (source, MediaType::from(specifier), None)
+      (source, MediaType::from(specifier), None, None)
     } else {
       let cache_filename = self.http_cache.get_cache_filename(specifier)?;
       let headers = get_remote_headers(&cache_filename)?;
@@ -307,13 +325,15 @@ impl Inner {
       let maybe_types = headers.get("x-typescript-types").map(|s| {
         analysis::resolve_import(s, &specifier, &self.maybe_import_map)
       });
-      (source, media_type, maybe_types)
+      let maybe_warning = headers.get("x-deno-warning").cloned();
+      (source, media_type, maybe_types, maybe_warning)
     };
     let mut metadata = Metadata::new(
       specifier,
       &source,
       &version,
       &media_type,
+      maybe_warning,
       &self.maybe_import_map,
     );
     if maybe_types.is_some() {
@@ -547,6 +567,23 @@ mod tests {
     assert_eq!(actual, Some((specifier_type, MediaType::Dts)))
   }
 
+  #[test]
+  fn test_warning_header() {
+    let (sources, location) = setup();
+    let cache = HttpCache::new(&location);
+    let specifier = resolve_url("https://deno.land/x/lib.js").unwrap();
+    let mut headers = HashMap::new();
+    headers.insert(
+      "x-deno-warning".to_string(),
+      "this is a warning".to_string(),
+    );
+    cache
+      .set(&specifier, headers, b"export const a = 1;")
+      .unwrap();
+    let actual = sources.get_maybe_warning(&specifier);
+    assert_eq!(actual, Some("this is a warning".to_string()));
+  }
+
   #[test]
   fn test_resolve_dependency_evil_redirect() {
     let (sources, location) = setup();
diff --git a/cli/tests/integration_tests_lsp.rs b/cli/tests/integration_tests_lsp.rs
index fa88ad17d4..d08da622f5 100644
--- a/cli/tests/integration_tests_lsp.rs
+++ b/cli/tests/integration_tests_lsp.rs
@@ -1604,6 +1604,74 @@ fn lsp_completions_registry_empty() {
   shutdown(&mut client);
 }
 
+#[test]
+fn lsp_diagnostics_warn() {
+  let _g = http_server();
+  let mut client = init("initialize_params.json");
+  did_open(
+    &mut client,
+    json!({
+      "textDocument": {
+        "uri": "file:///a/file.ts",
+        "languageId": "typescript",
+        "version": 1,
+        "text": "import * as a from \"http://127.0.0.1:4545/cli/tests/x_deno_warning.js\";\n\nconsole.log(a)\n",
+      },
+    }),
+  );
+  let (maybe_res, maybe_err) = client
+    .write_request::<_, _, Value>(
+      "deno/cache",
+      json!({
+        "referrer": {
+          "uri": "file:///a/file.ts",
+        },
+        "uris": [
+          {
+            "uri": "http://127.0.0.1:4545/cli/tests/x_deno_warning.js",
+          }
+        ],
+      }),
+    )
+    .unwrap();
+  assert!(maybe_err.is_none());
+  assert!(maybe_res.is_some());
+
+  let (method, _) = client.read_notification::<Value>().unwrap();
+  assert_eq!(method, "textDocument/publishDiagnostics");
+  let (method, _) = client.read_notification::<Value>().unwrap();
+  assert_eq!(method, "textDocument/publishDiagnostics");
+  let (method, maybe_params) = client
+    .read_notification::<lsp::PublishDiagnosticsParams>()
+    .unwrap();
+  assert_eq!(method, "textDocument/publishDiagnostics");
+  assert_eq!(
+    maybe_params,
+    Some(lsp::PublishDiagnosticsParams {
+      uri: Url::parse("file:///a/file.ts").unwrap(),
+      diagnostics: vec![lsp::Diagnostic {
+        range: lsp::Range {
+          start: lsp::Position {
+            line: 0,
+            character: 19
+          },
+          end: lsp::Position {
+            line: 0,
+            character: 70
+          }
+        },
+        severity: Some(lsp::DiagnosticSeverity::Warning),
+        code: Some(lsp::NumberOrString::String("deno-warn".to_string())),
+        source: Some("deno".to_string()),
+        message: "foobar".to_string(),
+        ..Default::default()
+      }],
+      version: Some(1),
+    })
+  );
+  shutdown(&mut client);
+}
+
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct PerformanceAverage {