diff --git a/core/object/class_db.cpp b/core/object/class_db.cpp
index 8c54db3c2cf..bf1bd0de93a 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -98,9 +98,24 @@ void ClassDB::get_class_list(List<StringName> *p_classes) {
 		p_classes->push_back(E.key);
 	}
 
-	p_classes->sort();
+	p_classes->sort_custom<StringName::AlphCompare>();
 }
 
+#ifdef TOOLS_ENABLED
+void ClassDB::get_extensions_class_list(List<StringName> *p_classes) {
+	OBJTYPE_RLOCK;
+
+	for (const KeyValue<StringName, ClassInfo> &E : classes) {
+		if (E.value.api != API_EXTENSION && E.value.api != API_EDITOR_EXTENSION) {
+			continue;
+		}
+		p_classes->push_back(E.key);
+	}
+
+	p_classes->sort_custom<StringName::AlphCompare>();
+}
+#endif
+
 void ClassDB::get_inheriters_from_class(const StringName &p_class, List<StringName> *p_classes) {
 	OBJTYPE_RLOCK;
 
diff --git a/core/object/class_db.h b/core/object/class_db.h
index 5c2c59d508b..7a4ee1afa45 100644
--- a/core/object/class_db.h
+++ b/core/object/class_db.h
@@ -251,6 +251,9 @@ public:
 	}
 
 	static void get_class_list(List<StringName> *p_classes);
+#ifdef TOOLS_ENABLED
+	static void get_extensions_class_list(List<StringName> *p_classes);
+#endif
 	static void get_inheriters_from_class(const StringName &p_class, List<StringName> *p_classes);
 	static void get_direct_inheriters_from_class(const StringName &p_class, List<StringName> *p_classes);
 	static StringName get_parent_class_nocheck(const StringName &p_class);
diff --git a/editor/doc_tools.cpp b/editor/doc_tools.cpp
index ef3981fd3f6..a7e3c03250f 100644
--- a/editor/doc_tools.cpp
+++ b/editor/doc_tools.cpp
@@ -355,20 +355,27 @@ static Variant get_documentation_default_value(const StringName &p_class_name, c
 	return default_value;
 }
 
-void DocTools::generate(bool p_basic_types) {
+void DocTools::generate(BitField<GenerateFlags> p_flags) {
+	// This may involve instantiating classes that are only usable from the main thread
+	// (which is in fact the case of the core API).
+	ERR_FAIL_COND(!Thread::is_main_thread());
+
 	// Add ClassDB-exposed classes.
 	{
 		List<StringName> classes;
-		ClassDB::get_class_list(&classes);
-		classes.sort_custom<StringName::AlphCompare>();
-		// Move ProjectSettings, so that other classes can register properties there.
-		classes.move_to_back(classes.find("ProjectSettings"));
+		if (p_flags.has_flag(GENERATE_FLAG_EXTENSION_CLASSES_ONLY)) {
+			ClassDB::get_extensions_class_list(&classes);
+		} else {
+			ClassDB::get_class_list(&classes);
+			// Move ProjectSettings, so that other classes can register properties there.
+			classes.move_to_back(classes.find("ProjectSettings"));
+		}
 
 		bool skip_setter_getter_methods = true;
 
 		// Populate documentation data for each exposed class.
 		while (classes.size()) {
-			String name = classes.front()->get();
+			const String &name = classes.front()->get();
 			if (!ClassDB::is_class_exposed(name)) {
 				print_verbose(vformat("Class '%s' is not exposed, skipping.", name));
 				classes.pop_front();
@@ -675,6 +682,10 @@ void DocTools::generate(bool p_basic_types) {
 		}
 	}
 
+	if (p_flags.has_flag(GENERATE_FLAG_SKIP_BASIC_TYPES)) {
+		return;
+	}
+
 	// Add a dummy Variant entry.
 	{
 		// This allows us to document the concept of Variant even though
@@ -683,11 +694,6 @@ void DocTools::generate(bool p_basic_types) {
 		class_list["Variant"].name = "Variant";
 	}
 
-	// If we don't want to populate basic types, break here.
-	if (!p_basic_types) {
-		return;
-	}
-
 	// Add Variant data types.
 	for (int i = 0; i < Variant::VARIANT_MAX; i++) {
 		if (i == Variant::NIL) {
diff --git a/editor/doc_tools.h b/editor/doc_tools.h
index 2d4a45bda00..5fffb6be382 100644
--- a/editor/doc_tools.h
+++ b/editor/doc_tools.h
@@ -45,7 +45,11 @@ public:
 	void add_doc(const DocData::ClassDoc &p_class_doc);
 	void remove_doc(const String &p_class_name);
 	bool has_doc(const String &p_class_name);
-	void generate(bool p_basic_types = false);
+	enum GenerateFlags {
+		GENERATE_FLAG_SKIP_BASIC_TYPES = (1 << 0),
+		GENERATE_FLAG_EXTENSION_CLASSES_ONLY = (1 << 1),
+	};
+	void generate(BitField<GenerateFlags> p_flags = {});
 	Error load_classes(const String &p_dir);
 	Error save_classes(const String &p_default_path, const HashMap<String, String> &p_class_path, bool p_include_xml_schema = true);
 
diff --git a/editor/editor_help.cpp b/editor/editor_help.cpp
index 0ab6e20b015..10ab733c2bd 100644
--- a/editor/editor_help.cpp
+++ b/editor/editor_help.cpp
@@ -2361,13 +2361,11 @@ void EditorHelp::_add_text(const String &p_bbcode) {
 }
 
 String EditorHelp::doc_version_hash;
-bool EditorHelp::doc_gen_first_attempt = true;
-bool EditorHelp::doc_gen_use_threads = true;
-Thread EditorHelp::gen_thread;
+Thread EditorHelp::worker_thread;
 
 void EditorHelp::_wait_for_thread() {
-	if (gen_thread.is_started()) {
-		gen_thread.wait_to_finish();
+	if (worker_thread.is_started()) {
+		worker_thread.wait_to_finish();
 	}
 }
 
@@ -2381,18 +2379,18 @@ String EditorHelp::get_cache_full_path() {
 }
 
 void EditorHelp::_load_doc_thread(void *p_udata) {
-	DEV_ASSERT(doc_gen_first_attempt);
-
 	Ref<Resource> cache_res = ResourceLoader::load(get_cache_full_path());
 	if (cache_res.is_valid() && cache_res->get_meta("version_hash", "") == doc_version_hash) {
 		Array classes = cache_res->get_meta("classes", Array());
 		for (int i = 0; i < classes.size(); i++) {
 			doc->add_doc(DocData::ClassDoc::from_dict(classes[i]));
 		}
+
+		// Extensions' docs are not cached. Generate them now (on the main thread).
+		callable_mp_static(&EditorHelp::_gen_extensions_docs).call_deferred();
 	} else {
-		// We have to go back to the main thread to start from scratch.
-		doc_gen_first_attempt = false;
-		callable_mp_static(&EditorHelp::generate_doc).bind(true).call_deferred();
+		// We have to go back to the main thread to start from scratch, bypassing any possibly existing cache.
+		callable_mp_static(&EditorHelp::generate_doc).bind(false).call_deferred();
 	}
 }
 
@@ -2406,6 +2404,12 @@ void EditorHelp::_gen_doc_thread(void *p_udata) {
 	cache_res->set_meta("version_hash", doc_version_hash);
 	Array classes;
 	for (const KeyValue<String, DocData::ClassDoc> &E : doc->class_list) {
+		if (ClassDB::class_exists(E.value.name)) {
+			ClassDB::APIType api = ClassDB::get_api_type(E.value.name);
+			if (api == ClassDB::API_EXTENSION || api == ClassDB::API_EDITOR_EXTENSION) {
+				continue;
+			}
+		}
 		classes.push_back(DocData::ClassDoc::to_dict(E.value));
 	}
 	cache_res->set_meta("classes", classes);
@@ -2415,14 +2419,15 @@ void EditorHelp::_gen_doc_thread(void *p_udata) {
 	}
 }
 
+void EditorHelp::_gen_extensions_docs() {
+	doc->generate((DocTools::GENERATE_FLAG_SKIP_BASIC_TYPES | DocTools::GENERATE_FLAG_EXTENSION_CLASSES_ONLY));
+}
+
 void EditorHelp::generate_doc(bool p_use_cache) {
 	OS::get_singleton()->benchmark_begin_measure("EditorHelp::generate_doc");
-	if (doc_gen_use_threads) {
-		// In case not the first attempt.
-		_wait_for_thread();
-	}
 
-	DEV_ASSERT(doc_gen_first_attempt == (doc == nullptr));
+	// In case not the first attempt.
+	_wait_for_thread();
 
 	if (!doc) {
 		doc = memnew(DocTools);
@@ -2432,24 +2437,14 @@ void EditorHelp::generate_doc(bool p_use_cache) {
 		_compute_doc_version_hash();
 	}
 
-	if (p_use_cache && doc_gen_first_attempt && FileAccess::exists(get_cache_full_path())) {
-		if (doc_gen_use_threads) {
-			gen_thread.start(_load_doc_thread, nullptr);
-		} else {
-			_load_doc_thread(nullptr);
-		}
+	if (p_use_cache && FileAccess::exists(get_cache_full_path())) {
+		worker_thread.start(_load_doc_thread, nullptr);
 	} else {
 		print_verbose("Regenerating editor help cache");
-
-		// Not doable on threads unfortunately, since it instantiates all sorts of classes to get default values.
-		doc->generate(true);
-
-		if (doc_gen_use_threads) {
-			gen_thread.start(_gen_doc_thread, nullptr);
-		} else {
-			_gen_doc_thread(nullptr);
-		}
+		doc->generate();
+		worker_thread.start(_gen_doc_thread, nullptr);
 	}
+
 	OS::get_singleton()->benchmark_end_measure("EditorHelp::generate_doc");
 }
 
diff --git a/editor/editor_help.h b/editor/editor_help.h
index 1f813f930c6..d2d05a86031 100644
--- a/editor/editor_help.h
+++ b/editor/editor_help.h
@@ -188,13 +188,12 @@ class EditorHelp : public VBoxContainer {
 	void _toggle_scripts_pressed();
 
 	static String doc_version_hash;
-	static bool doc_gen_first_attempt;
-	static bool doc_gen_use_threads;
-	static Thread gen_thread;
+	static Thread worker_thread;
 
 	static void _wait_for_thread();
 	static void _load_doc_thread(void *p_udata);
 	static void _gen_doc_thread(void *p_udata);
+	static void _gen_extensions_docs();
 	static void _compute_doc_version_hash();
 
 protected:
diff --git a/main/main.cpp b/main/main.cpp
index 7b469579048..900f9b27146 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -2768,7 +2768,7 @@ bool Main::start() {
 
 #ifdef TOOLS_ENABLED
 	String doc_tool_path;
-	bool doc_base = true;
+	BitField<DocTools::GenerateFlags> gen_flags;
 	String _export_preset;
 	bool export_debug = false;
 	bool export_pack_only = false;
@@ -2793,7 +2793,7 @@ bool Main::start() {
 			check_only = true;
 #ifdef TOOLS_ENABLED
 		} else if (args[i] == "--no-docbase") {
-			doc_base = false;
+			gen_flags.set_flag(DocTools::GENERATE_FLAG_SKIP_BASIC_TYPES);
 #ifndef DISABLE_DEPRECATED
 		} else if (args[i] == "--convert-3to4") {
 			converting_project = true;
@@ -2904,7 +2904,7 @@ bool Main::start() {
 
 		Error err;
 		DocTools doc;
-		doc.generate(doc_base);
+		doc.generate(gen_flags);
 
 		DocTools docsrc;
 		HashMap<String, String> doc_data_classes;