Data validators
Validates data of different types
Validation APIs check data before you store or use it: phone numbers, bank account numbers (IBAN), EU VAT numbers, names, addresses, spelling and HTML. Use them in forms and imports to catch typos and fake entries early.
Address Validation Plus
DOTS Address Validation Plus by Service Objects is a real-time web service API that enables companies to validate, correct and standardize address data, pinpoint customer address locations with geocoding, and append demographic ...
DNS over HTTPS (Google Public DNS)
Google Public DNS answers DNS queries over HTTPS with a simple JSON API: request dns.google/resolve?name=example.com&type=MX and get back the records. Look up A, AAAA, MX, TXT, CNAME, NS and other record types, with DNSSEC ...
LanguageTool API
LanguageTool checks texts for grammar, spelling, punctuation and style in more than 30 languages, including English, German, French, Spanish and Dutch. Send text to the check endpoint and get back the errors found, with ...
Name API
NameAPI helps you handle people's names in your software. It can parse a full name into given name and surname, detect the likely gender, check whether two names match, format names correctly and recognise e-mail addresses that ...
Nu HTML Checker (W3C)
The Nu HTML Checker is the validator behind validator.w3.org/nu. Send it an HTML, CSS or SVG document, or a URL to check, and get back the errors and warnings in JSON, XML or text, with line and column numbers. Useful for ...
numverify
numverify checks phone numbers from 230+ countries: whether a number is valid, its international and local format, country, location, carrier and line type (mobile or landline). Responses are JSON. The free plan gives 100 ...
OpenIBAN
OpenIBAN checks whether an IBAN (international bank account number) is valid, using its length and checksum, and for several countries returns the bank code, BIC and bank name. One simple GET request per IBAN, for example ...
VIES VAT number validation
VIES, run by the European Commission, checks whether a VAT number from an EU member state (and Northern Ireland) is valid, and for most countries returns the registered company name and address. Call it with a POST request to the ...
Compare the validation APIs
| Service | API key | Formats | Free use |
|---|---|---|---|
| Address Validation Plus | – | – | Free to try. |
| DNS over HTTPS (Google Public DNS) | Not needed | JSON | Free, no key needed. |
| LanguageTool API | Not needed | JSON | – |
| Name API | – | XML | Free and paid plans. |
| Nu HTML Checker (W3C) | – | – | Free and open source; for heavy use, run your own copy of the checker. |
| numverify | Needed, free | JSON | The free plan gives 100 requests per month with a free API key, without a time limit; paid plans give more requests. |
| OpenIBAN | Not needed | JSON | Free and open source, no key needed. |
| VIES VAT number validation | Not needed | JSON, XML | Free, no key needed. |
Questions
Which free validation APIs work without an API key?
DNS over HTTPS (Google Public DNS), LanguageTool API, OpenIBAN and VIES VAT number validation work without a key, according to their documentation. Most keyless services ask you to keep the number of requests reasonable, and some ask for a User-Agent that names your app.
Are these validation APIs really free?
The services here can be used without paying, at least on a free plan or free tier, often with limits such as a number of requests per day or non-commercial use only. The table above quotes what each service says about its free use; check the provider's own terms before you rely on it.
How up to date is this list?
The address of every service is checked about once a week, and services that stop working or stop being free are removed. This list last changed on November 1st, 2026.