Для валидации полей, есть валидатор
public function store(Request $request, StoreBlogTag $store)
{
$validate = Validator::make($request->all(), $store->rules(), $store->messages());
if ($validate->fails()) {
return redirect('post/create')
->withErrors($validate)
->withInput();
};
$tag = Tag::firstOrCreate([
'title' => $request->input('title'),
'slug' => Str::slug($request->input('title'), '-'),
]);
$tag->save();
return redirect()->back();
}