Check if a phone number exists on WhatsApp

GET 
/api/sessions/:sessionId/contacts/check/:number

Returns whether the number is a registered WhatsApp account and its canonical id. Use this to pre-validate a recipient before sending: the send endpoints return 201 on accepting a message even for numbers that are not on WhatsApp, so this is the only way to confirm a new number is reachable before you send to it.

Request

Responses

200

Number existence check result

409

The session is not connected — an engine exists for it but is not ready: disconnected, reconnecting, or still initializing, so the request never reached WhatsApp. Wait for ready and retry. A session that was never started answers 400 instead, and the session lifecycle routes answer 409 for a conflicting state rather than this. One window answers this while the session still reads ready: WhatsApp Web periodically reloads its own page and the engine re-injects into it — for those few seconds the answer is a 409 naming the reload; retry shortly.

503

WhatsApp did not answer the lookup. Deliberately not reported as exists: false — that would be a claim about the number rather than about the query, and this route exists to be trusted before a send.