Index: clangd/ClangdLSPServer.cpp
===================================================================
--- clangd/ClangdLSPServer.cpp
+++ clangd/ClangdLSPServer.cpp
@@ -506,6 +506,8 @@
         }
         LSPDiag["clangd_fixes"] = std::move(ClangdFixes);
       }
+      if (!Diag.category.empty())
+        LSPDiag["category"] = Diag.category;
       DiagnosticsJSON.push_back(std::move(LSPDiag));
 
       auto &FixItsForDiagnostic = LocalFixIts[Diag];
Index: clangd/Diagnostics.h
===================================================================
--- clangd/Diagnostics.h
+++ clangd/Diagnostics.h
@@ -37,6 +37,7 @@
   std::string File;
   clangd::Range Range;
   DiagnosticsEngine::Level Severity = DiagnosticsEngine::Note;
+  std::string Category;
   // Since File is only descriptive, we store a separate flag to distinguish
   // diags from the main file.
   bool InsideMainFile = false;
Index: clangd/Diagnostics.cpp
===================================================================
--- clangd/Diagnostics.cpp
+++ clangd/Diagnostics.cpp
@@ -226,6 +226,7 @@
     clangd::Diagnostic Res;
     Res.range = D.Range;
     Res.severity = getSeverity(D.Severity);
+    Res.category = D.Category;
     return Res;
   };
 
@@ -292,6 +293,9 @@
     D.InsideMainFile = InsideMainFile;
     D.File = Info.getSourceManager().getFilename(Info.getLocation());
     D.Severity = DiagLevel;
+    D.Category = DiagnosticIDs::getCategoryNameFromID(
+                     DiagnosticIDs::getCategoryNumberForDiag(Info.getID()))
+                     .str();
     return D;
   };
 
Index: clangd/Protocol.h
===================================================================
--- clangd/Protocol.h
+++ clangd/Protocol.h
@@ -544,6 +544,12 @@
 
   /// The diagnostic's message.
   std::string message;
+
+  /// The diagnostic's category. Can be omitted.
+  /// An LSP extension that's used to send the name of the category over to the
+  /// client. The category typically describes the compilation stage during
+  /// which the issue was produced, e.g. "Semantic Issue" or "Parse Issue".
+  std::string category;
 };
 
 /// A LSP-specific comparator used to find diagnostic in a container like
Index: test/clangd/compile-commands-path-in-initialize.test
===================================================================
--- test/clangd/compile-commands-path-in-initialize.test
+++ test/clangd/compile-commands-path-in-initialize.test
@@ -23,6 +23,7 @@
 # CHECK-NEXT:   "params": {
 # CHECK-NEXT:     "diagnostics": [
 # CHECK-NEXT:       {
+# CHECK-NEXT:         "category": "#pragma message Directive",
 # CHECK-NEXT:         "message": "MACRO is one",
 ---
 {"jsonrpc":"2.0","id":0,"method":"workspace/didChangeConfiguration","params":{"settings":{"compilationDatabasePath":"INPUT_DIR/build-2"}}}
@@ -30,6 +31,7 @@
 # CHECK-NEXT:   "params": {
 # CHECK-NEXT:     "diagnostics": [
 # CHECK-NEXT:       {
+# CHECK-NEXT:         "category": "#pragma message Directive",
 # CHECK-NEXT:         "message": "MACRO is two",
 ---
 {"jsonrpc":"2.0","id":10000,"method":"shutdown"}
Index: test/clangd/compile-commands-path.test
===================================================================
--- test/clangd/compile-commands-path.test
+++ test/clangd/compile-commands-path.test
@@ -23,6 +23,7 @@
 # CHECK-NEXT:   "params": {
 # CHECK-NEXT:     "diagnostics": [
 # CHECK-NEXT:       {
+# CHECK-NEXT:         "category": "#pragma message Directive",
 # CHECK-NEXT:         "message": "MACRO is not defined",
 ---
 {"jsonrpc":"2.0","id":0,"method":"workspace/didChangeConfiguration","params":{"settings":{"compilationDatabasePath":"INPUT_DIR/build-1"}}}
@@ -30,6 +31,7 @@
 # CHECK-NEXT:   "params": {
 # CHECK-NEXT:     "diagnostics": [
 # CHECK-NEXT:       {
+# CHECK-NEXT:         "category": "#pragma message Directive",
 # CHECK-NEXT:         "message": "MACRO is one",
 ---
 {"jsonrpc":"2.0","id":0,"method":"workspace/didChangeConfiguration","params":{"settings":{"compilationDatabasePath":"INPUT_DIR/build-2"}}}
@@ -37,6 +39,7 @@
 # CHECK-NEXT:   "params": {
 # CHECK-NEXT:     "diagnostics": [
 # CHECK-NEXT:       {
+# CHECK-NEXT:         "category": "#pragma message Directive",
 # CHECK-NEXT:         "message": "MACRO is two",
 ---
 {"jsonrpc":"2.0","id":10000,"method":"shutdown"}
Index: test/clangd/diagnostics.test
===================================================================
--- test/clangd/diagnostics.test
+++ test/clangd/diagnostics.test
@@ -6,6 +6,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Return type of 'main' is not 'int'",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {
Index: test/clangd/did-change-configuration-params.test
===================================================================
--- test/clangd/did-change-configuration-params.test
+++ test/clangd/did-change-configuration-params.test
@@ -24,6 +24,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Variable 'i' is uninitialized when used here",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {
Index: test/clangd/execute-command.test
===================================================================
--- test/clangd/execute-command.test
+++ test/clangd/execute-command.test
@@ -6,6 +6,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Using the result of an assignment as a condition without parentheses",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {
Index: test/clangd/extra-flags.test
===================================================================
--- test/clangd/extra-flags.test
+++ test/clangd/extra-flags.test
@@ -6,6 +6,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Variable 'i' is uninitialized when used here",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {
@@ -28,6 +29,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Variable 'i' is uninitialized when used here",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {
Index: test/clangd/fixits.test
===================================================================
--- test/clangd/fixits.test
+++ test/clangd/fixits.test
@@ -6,6 +6,7 @@
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [
 # CHECK-NEXT:      {
+# CHECK-NEXT:        "category": "Semantic Issue",
 # CHECK-NEXT:        "message": "Using the result of an assignment as a condition without parentheses",
 # CHECK-NEXT:        "range": {
 # CHECK-NEXT:          "end": {