How to check if a phone number is on WhatsApp
You have a phone number and one question: does it have WhatsApp? Maybe it's a lead, a supplier, or a customer who filled in a form. Here's how to get the answer in one request, for one number or ten thousand.
Ask the API
wtsp.dev answers with a plain yes or no:
curl "https://wtsp.dev/v1/exists?phone=447400123456" \ -H "Authorization: Bearer $WTSP_API_KEY"{ "phone": "+447400123456", "hasWhatsApp": true}Each answer costs 0.004 USDC, so checking 1,000 numbers costs $4. "Not on WhatsApp" is an answer and is charged too, because a no is as useful as a yes when you're cleaning a list. A malformed number is turned away before you pay, and a lookup that doesn't get an answer costs nothing.
There's no account to create. Buy prepaid credit for a key on the API keys section, or let an AI agent pay per request from its own wallet.
Need more than yes or no?
/v1/profile(0.006 USDC) adds the account type, the about text and, for businesses, the full public profile: name, description, categories, email, websites, address and opening hours./v1/profile/full(0.01 USDC) adds the profile photo.
Start with /v1/exists, the cheapest call, and only fetch profiles for the numbers that say yes.
Write numbers with their country code
07400 123456 is a UK number to someone in London and nothing at all to WhatsApp. Add the country code and drop the leading zero: 447400123456. Spaces, dashes and a leading + are fine.
Each country page under lookups by country shows its calling code and a sample number you can paste.
What about checking by hand?
You can save a number in your phone and see whether WhatsApp lists it. It works for one number. It doesn't work for a spreadsheet: every check fills your address book with strangers, takes a minute of tapping, and gives your CRM or agent nothing it can read. Past a handful of numbers, the API is faster and costs less than your time.
Try it on the playground without signing up, or give your agent the wtsp skill and let it check numbers itself.