特定パス以下のActionController::RoutingErrorでJSONを返却する - Qiita

module YourNameSpace::Middleware class RoutingErrorResponseJson RESPONSE_JSON_PATHS = %w[/api/v1] def initialize(app) @app = app end def call(env) request = ActionDispatch::Request.new(env) status, headers, response = @app.call(env) # NOTE: ActionController::RoutingError時に設定されるパラメータ # See https://github.com/rails/rails/blob/5-2-stable/actionpack/lib/action_dispatch/journey/router.rb#L64 if enable?