Hi Vlad, you can customize the serializer in the application package by setting the engine config first, then the serializer option:

# in MyApp::Controller
use Dancer2;

set engines => {
    serializer => {
        JSON => {
                pretty        => 1,
                allow_blessed => 1,
                canonical     => 0,
                utf8          => 1,
        },
    },
};
set serializer => 'JSON';

get '/config' => sub {
    return config;
};
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Output in browser when requesting /config is something like:

{
   "apphandler" : "PSGI",

   # bunch of stuff snipped ...

   "engines" : {
      "serializer" : {
         "JSON" : {
            "utf8" : 1,
            "canonical" : 0,
            "allow_blessed" : 1,
            "pretty" : 1
         }
      }
   },
   "serializer" : null,
   "static_handler" : 1,
   "host" : "0.0.0.0"
}
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Note that, oddly, the config shows the value of serializer as null, but as the format of the output shows, the settings are being implemented.

Hope this helps!