Swap mk_live_ for mk_test_ and everything runs exactly as it would live: the request is validated, the content is classified, the message is threaded, events fire and your webhooks receive them. Nothing leaves the building and nothing is billed.
The field to check
On a test send, read classifier_warning on the response. That is how a sandbox send tells you the same message would have been refused live — it is the cheapest possible way to find out that your template reads as marketing, before a real customer is waiting on it.
What test mode does not do
It does not deliver. No recipient ever receives a test send.
It does not count toward your monthly quota and never appears on an invoice.
It does not hit production webhook endpoints that you have not subscribed for test traffic.
Test messages show up in the dashboard alongside live ones so you can inspect exactly what would have gone out.
Open the message log