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Validate phone numbers on signup forms

Published 2026-10-17

People type phone numbers every way possible: with spaces, dots, brackets, a leading 0, or without the country code. If you store them as typed, SMS tools and CRMs choke later. ContactLint parses the number once at signup and gives you one clean format to store.

What you get back

curl -X POST https://contactlint.com/v1/phone/validate \
  -H "Authorization: Bearer YOUR_KEY" -H "content-type: application/json" \
  -d '{"phone":"(816) 555-0134","country":"US"}'

{
  "input": "(816) 555-0134",
  "parsed": true,
  "valid": true,
  "possible": true,
  "type": "FIXED_LINE_OR_MOBILE",
  "region": "US",
  "country_calling_code": "+1",
  "e164": "+18165550134",
  "national": "(816) 555-0134",
  "international": "+1 816 555 0134"
}

That is the result object; the API wraps it with a usage object. Pass country (ISO code such as US, GB or DE) for numbers typed without a country code. Store e164.

How to use each field

• valid false: ask the user to check the number. possible true but valid false usually means the length is right but the range is not in use.
• type: MOBILE, FIXED_LINE, TOLL_FREE, VOIP and others from the numbering plan. In the US and Canada, the plan does not separate mobile from landline, so most numbers come back FIXED_LINE_OR_MOBILE.
• region: the country or territory the number belongs to, useful for spotting a mismatch with the billing country.

What it does not do

The check uses libphonenumber metadata only. It does not call carriers, so it cannot tell whether a number is in service, who the carrier is, or whether it was ported. To prove a person owns the number, you still need a one-time code by SMS or voice. For more on each field, read the phone number validation API guide, or test a number with the free phone number validator.

Email and phone on one key

The same key and balance cover email checks, so a signup form can check both fields. Each number checked uses one check: 100 free per key each month, then credit packs from $9 for 5,000.

Questions

Does it tell me if a number is a mobile?

Where the numbering plan says so, yes. In the US and Canada most numbers return FIXED_LINE_OR_MOBILE because the plan does not separate them.

Does it send an SMS?

No. It never contacts the number. Use an OTP service if you need to prove ownership.

Which countries are supported?

All countries in the libphonenumber metadata, which covers the international numbering plans.

Get a free API key. 100 checks per month, no card required. Or try a live check first.