Rescue Exception instead of RuntimeError
Load Rack middleware by default

so we can use it in Rack easily

require 'rack'
require 'trackets'

Trackets.setup do |config|
  config.api_key = "insert-valid-api-key"
end

app = Rack::Builder.app do
  run lambda { |env| raise "Testing Error" }
end

use Trackets::Middleware::RackExceptionHandler
run app
Add comment about using middleware in Rack app