diff --git a/crates/rust-analyzer/src/diagnostics/to_proto.rs b/crates/rust-analyzer/src/diagnostics/to_proto.rs
index 93bef5c8b4..d3720de33e 100644
--- a/crates/rust-analyzer/src/diagnostics/to_proto.rs
+++ b/crates/rust-analyzer/src/diagnostics/to_proto.rs
@@ -2,7 +2,7 @@
 //! `cargo check` json format to the LSP diagnostic format.
 use std::{collections::HashMap, path::Path};
 
-use flycheck::{Applicability, DiagnosticLevel, DiagnosticSpan};
+use flycheck::{Applicability, DiagnosticCode, DiagnosticLevel, DiagnosticSpan};
 use stdx::format_to;
 
 use crate::{lsp_ext, to_proto::url_from_abs_path};
@@ -211,6 +211,8 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         }
     }
 
+    let code_description = rustc_code_description(rd.code.as_ref());
+
     primary_spans
         .iter()
         .map(|primary_span| {
@@ -248,7 +250,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                         range: in_macro_location.range,
                         severity,
                         code: code.clone().map(lsp_types::NumberOrString::String),
-                        code_description: None,
+                        code_description: code_description.clone(),
                         source: Some(source.clone()),
                         message: message.clone(),
                         related_information: Some(information_for_additional_diagnostic),
@@ -269,7 +271,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                 range: location.range,
                 severity,
                 code: code.clone().map(lsp_types::NumberOrString::String),
-                code_description: None,
+                code_description: code_description.clone(),
                 source: Some(source.clone()),
                 message,
                 related_information: if related_information.is_empty() {
@@ -292,6 +294,20 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         .collect()
 }
 
+fn rustc_code_description(code: Option<&DiagnosticCode>) -> Option<lsp_types::CodeDescription> {
+    code.filter(|c| {
+        let mut chars = c.code.chars();
+        chars.next().map_or(false, |c| c == 'E')
+            && chars.by_ref().take(4).all(|c| c.is_ascii_digit())
+            && chars.next().is_none()
+    })
+    .and_then(|c| {
+        lsp_types::Url::parse(&format!("https://doc.rust-lang.org/error-index.html#{}", c.code))
+            .ok()
+            .map(|href| lsp_types::CodeDescription { href })
+    })
+}
+
 #[cfg(test)]
 #[cfg(not(windows))]
 mod tests {