Look up what a number supports

Ask what a phone number can receive, before you send to it. Works on any number in the world — it doesn’t have to be one of your Dial numbers, and you don’t have to have messaged it before.

supports describes the number you asked about, not your own line. Each key is a channel, and the value says whether that number can be reached there. Today the keys are imessage and whatsapp; further channels arrive as further keys, so read the ones you care about by name rather than assuming the whole set.

The answer is point-in-time, not a property of the number. true means the number is reachable on that channel as of this request — someone who changes device or turns the service off stops being reachable, and the same number can answer differently next week. Treat it as a strong signal for picking a channel, not as a promise that a later send lands.

A lookup that fails is never reported as a verdict. If Dial can’t complete a check — on either channel — the whole request fails with a 502, and a rate-limited request fails with a 429. So false always means “we asked, and the number isn’t reachable there” — never “we couldn’t find out”.