Simulate slow or flaky backends

[[rules]]
when.request.url_path = "/fast"
respond.text = "instant response"

[[rules]]
when.request.url_path = "/slow"
respond = { text = "eventually...", delay_response_milliseconds = 800 }

respond.delay_response_milliseconds sleeps before responding — useful for exercising a client’s timeout, retry, or loading-state handling against a predictable, artificial delay.

Set it per rule, on respond. A rule-set-wide [default] delay_response_milliseconds also exists in the schema, but currently has no effect on any response — see Rule-set schema.

There’s no built-in mechanism for a genuinely flaky backend (randomly failing a fraction of requests) — only a fixed, deterministic delay. If you need actual failure injection, Rhai middleware can implement it directly.

A worked, verified example with three endpoints at increasing delays: crates/apimock/examples/simulate-slow-backend/.