♪ II · Verify

WhatsApp checker. A firm yes or no.

Give a phone number, get whether it has a WhatsApp account. The answer comes from WhatsApp's own contact discovery, so a no is as firm as a yes. When a number can't be checked, unknown comes back free.

A firm verdict from the protocol · unknown = free

mozartemail.com / whatsapp-checklive demo: click to take over

1 · Fill in → 2 · Run it

phone number → on WhatsApp or not · a firm yes or no, never a guess

Start free with 50 verified credits

No credit card required · 50 free credits

The problem

A column of numbers tells you nothing.

Elsewhere

A phone list on its own says nothing about whether a number can be reached on WhatsApp. Guess wrong and you either skip a reachable prospect or waste a message on a number that was never there.

At Mozart

Mozart asks WhatsApp's own contact discovery, the same request the app makes when it syncs your address book. on_whatsapp and not_on_whatsapp are both firm answers at 0.5 credit. A number that can't be checked comes back unknown and costs nothing.

The mechanism

How a verdict is earned.

1

Normalise

The number is put into E.164 form first, so a local 06 and a +33 6 are the same lookup.

2

Ask the protocol

A linked account queries WhatsApp's contact discovery, the request the app itself makes on sync.

3

Read the answer

WhatsApp returns only the numbers that have an account, so a number left out of the answer is a firm absence.

4

The verdict

on_whatsapp or not_on_whatsapp: 0.5 credit. Number unreadable or the service unreachable: unknown, 0 credits.

Side by side

A guess against a verdict.

ElsewhereAt Mozart
A number assumed reachable because it looks like a mobilethe protocol asked, one number at a time
No answer treated as a noa firm no, separate from an honest unknown
Every row billed, hit or missa firm verdict is billed, unknown is free
A message sent to find outno message sent, the number is never contacted
Measured, not promised

yes / no

a firm verdict, or unknown

The check uses WhatsApp's own contact-discovery request. A number the protocol does not return is a firm absence, not a maybe. When the check can't run, the answer is unknown, and unknown is never billed.

Start free with 50 verified creditsHow it's proven →

No credit card required · 50 free credits

Single · bulk · API

One number, a list, or your own code.

Single

Paste a phone number in the widget above and read the verdict, live, three free runs a day.

Bulk

5 000 numbers per file, two firm verdicts per credit, unknown rows free. The job keeps running after you close the tab.

API

POST /api/whatsapp takes one phone and returns result, on_whatsapp and the E.164 number it checked, so a firm no and an unreadable number never look alike in your logs.

POST /api/whatsapp
{"phone": "+33 6 12 34 56 78"}
200 OK
{
"ok": true, "billable": true, "charged": 0.5,
"result": "on_whatsapp", "on_whatsapp": true,
"phone_norm": "33612345678"
}

Explore the API →

Where it fits

Before you pick a channel.

SDR teamsSplit a phone list into the numbers worth a WhatsApp message and the ones to reach another way.
AgenciesHand a client a phone list tagged reachable or not, with a firm verdict per row.
RevOpsEnrich CRM contacts with a WhatsApp flag, and pay nothing on the numbers that can't be checked.

Compose with

Reverse lookup → WhatsApp checker → Email verifier

Find the number, then learn whether WhatsApp can reach it.

Questions, answered whole

What list owners ask.

Is a not_on_whatsapp verdict billed?−

Yes, 0.5 credit, the same as on_whatsapp. A firm no is a delivered answer: knowing a number is not on WhatsApp is what lets you pick another channel. Only unknown, where no verdict exists, is free.

Does the check send a message to the number?+

No. It uses WhatsApp's contact-discovery request, the same one the app makes when it syncs your contacts. The number is never messaged and never notified.

What does unknown mean?+

That no firm answer could be produced: an unparseable number, or the checking service momentarily unreachable or rate-limited. unknown costs nothing, so a hiccup never bills you and never invents a false no.

How firm is a no?+

WhatsApp returns only the numbers that have an account, so a number left out of the answer is a genuine absence, not a timeout dressed up as a no. A network problem is reported as unknown instead.

How much does a 5 000-number list cost?+

At most 2 500 credits, since a firm verdict is 0.5 credit. In practice it lands lower: every number that can't be checked comes back unknown and deducts nothing.

A firm yes or no.
unknown costs 0.

Know which numbers WhatsApp can reach, before you send.

Start free with 50 verified credits

No credit card required · 50 free credits