A signup form can accept an email address that doesn’t exist, an invalid phone number, or a VAT number that doesn’t match a registered business. Basic format checks aren’t always enough to determine whether user-submitted information can be trusted.
For developers building signup, checkout, or KYC flows, validating user data requires more than basic checks. A phone validation API checks number details, while an email verification API assesses deliverability. VAT and device checks add further context.
In this guide, we compare four identity verification APIs, Numverify, Mailboxlayer, Vatlayer, and Userstack, based on their features, API responses, and pricing to help you choose the right fit.
Key Takeaways
- Numverify validates phone numbers and returns country, location, carrier, and line type data.
- Mailboxlayer checks email syntax, MX records, SMTP status, disposable providers, role addresses, and deliverability.
- Vatlayer validates VAT numbers and returns company information.
- Userstack parses User Agent strings to identify devices, browsers, operating systems, and crawler data.
- Each API has a free tier, but HTTPS availability differs by product and plan.
Identity verification APIs compared
API | Best for | Data returned | Free tier | HTTPS | Response |
Numverify | Phone validation | Validity, country, location, carrier, line type | 100 requests/month | Paid plans | JSON |
Mailboxlayer | Email verification | Syntax, MX, SMTP, catch all, disposable, role, score | 100 requests/month | Yes | JSON |
Vatlayer | VAT validation | Validity, VAT number, company name, company address | 100 requests/month | Paid plans | JSON |
Userstack | Device detection | Device, browser, OS, crawler data | 100 lookups/month | Yes | JSON/XML |
Current paid entry plans start at $14.99 per month for Numverify, $14.99 for Mailboxlayer, $9.99 for Vatlayer, and $9.99 for Userstack.
Numverify: phone validation API
Numverify is a phone validation API for national and international numbers. It returns validity, country, location, carrier, and line type in one JSON response.
Send the number to the current validate endpoint:
curl "http://apilayer.net/api/validate?access_key=YOUR_ACCESS_KEY&number=14158586273"
The official documentation publishes this response:
{
"valid": true,
"number": "14158586273",
"local_format": "4158586273",
"international_format": "+14158586273",
"country_prefix": "+1",
"country_code": "US",
"country_name": "United States of America",
"location": "Novato",
"carrier": "AT&T Mobility LLC",
"line_type": "mobile"
}
The free plan includes 100 requests per month. The Basic plan starts at $14.99 per month for 5,000 requests and adds HTTPS encryption.
Read the Numverify documentation.
How do I verify an email address without sending an email?
Use Mailboxlayer to check syntax, MX records, and SMTP status without sending a message.
Mailboxlayer also identifies catch all domains, disposable addresses, role accounts, free providers, and email quality.
curl "https://apilayer.net/api/check?access_key=YOUR_ACCESS_KEY&email=support@apilayer.com"
A published Mailboxlayer response for this address returns:
{
"email": "support@apilayer.com",
"did_you_mean": "",
"format_valid": true,
"mx_found": true,
"smtp_check": true,
"catch_all": false,
"role": true,
"disposable": false,
"free": false,
"score": 0.8
}
That gives a signup flow several independent checks instead of treating a correctly formatted address as proof that the mailbox is usable.
Mailboxlayer is part of the APILayer suite, with one account, one API key, one dashboard, and one invoice.
The free tier includes 100 requests. The current Starter plan costs $14.99 per month for 5,000 requests.
Read the Mailboxlayer documentation.
Vatlayer: VAT validation API
Vatlayer is a VAT validation API for checking a VAT number and retrieving associated company data.
curl "http://apilayer.net/api/validate?access_key=YOUR_ACCESS_KEY&vat_number=LU26375245"
Vatlayer publishes this real response:
{
"valid": true,
"database": "ok",
"format_valid": true,
"query": "LU26375245",
"country_code": "LU",
"vat_number": "26375245",
"company_name": "AMAZON EUROPE CORE S.A R.L.",
"company_address": "5, RUE PLAETIS L-2338 LUXEMBOURG"
}
Check the database field before rejecting a VAT number. If it returns failure, the database was unavailable, not necessarily the VAT number invalid.
For B2B signup or checkout, your backend can compare the returned company details with the information supplied by the customer.
The free plan includes 100 requests per month. Paid plans start at $9.99 per month for 1,000 requests and include HTTPS encryption.
Read the Vatlayer documentation.
Table of Contents
Userstack: device detection API
Userstack is a device detection API that parses a User Agent string into structured device, browser, operating system, and crawler data.
curl --get "https://api.userstack.com/detect" \
--data-urlencode "access_key=YOUR_ACCESS_KEY" \
--data-urlencode "ua=Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36"
The example response published by Userstack includes:
{
"type": "browser",
"os": {
"name": "macOS 10.14 Mojave",
"family": "macOS"
},
"device": {
"is_mobile_device": false,
"type": "desktop",
"brand": "Apple",
"name": "Mac"
},
"browser": {
"name": "Chrome",
"version": "70.0.3538.110",
"version_major": "70",
"engine": "WebKit/Blink"
},
"crawler": {
"is_crawler": false,
"category": null,
"last_seen": null
}
}
Use the result when your backend needs device or browser context around a session. The free plan includes 100 lookups per month and HTTPS. The Basic plan starts at $9.99 per month for 50,000 lookups and adds crawler detection.
Read the Userstack documentation.
Which identity verification API should you use?
Use Numverify for phone numbers, Mailboxlayer for email addresses, Vatlayer for VAT numbers, and Userstack for device context.
For flows that need more context, combine signals. A B2B signup can validate an email and VAT number, check the contact phone number, and add device data before accepting the account.
No single result proves a person’s identity. These APIs validate specific inputs so your backend can make decisions using cleaner data.
Explore APILayer Products
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FAQ
What is the best API for phone number validation in 2026?
Numverify is built for phone number validation. It checks validity and returns country, location, carrier, and line type data.
How do I verify an email address without sending an email?
Mailboxlayer checks syntax, MX records, and SMTP status without sending a message. It also identifies disposable addresses, role accounts, free providers, and catch all domains.
Can I validate a VAT number through an API?
Yes. Vatlayer validates VAT numbers and returns associated company information when available.
What is device detection and when do I need it?
Device detection turns a User Agent string into structured device, browser, and operating system data. Use it when your application needs client context for routing, analytics, security rules, or user experience decisions.
How much do identity verification APIs cost?
All four APIs in this comparison have free plans. Current paid entry plans start at $9.99 per month for Vatlayer and Userstack, and $14.99 per month for Numverify and Mailboxlayer.