I built free email, phone & card validators + a tiny hosted API (with real MX deliverability)

Choi Changhwan — Fri, 03 Jul 2026 02:02:47 +0000

I kept needing the same small checks in side projects — is this email real, is this phone number formatted right, is this card number even valid — so I built a set of free tools and put the same logic behind a tiny hosted API. Sharing in case it saves someone else time.

Live tools (no signup): https://tools-site.cchkjjdobby.workers.dev

What it does

Email — syntax, disposable/role detection, typo suggestions (gmial.com → gmail.com), and a real MX-record deliverability check (not just regex).
Phone — E.164 formatting + country detection for 35+ countries.
Card — Luhn checksum + brand detection (Visa, Mastercard, Amex…). Format-level only.
Bonus — an SEO/readability text analyzer (Flesch, reading time, keyword density) that also works on Korean.

Using the API

One GET call, JSON back, CORS enabled:

GET https://verify-api.cchkjjdobby.workers.dev/email?email=test@mailinator.com

{
  "domain": "mailinator.com",
  "is_disposable": true,
  "has_mx": true,
  "status": "disposable",
  "deliverable": false
}

Docs: https://tools-site.cchkjjdobby.workers.dev/docs

Honest limitations

Card check is format/Luhn/brand only — it does not confirm a card is real or active.
Phone validation is length/prefix-based, not carrier-level.
The email MX check estimates deliverability; it can't guarantee an inbox exists.

It runs on Cloudflare Workers with no paid external calls, so the free tier is real and it stays fast.

Would love feedback — especially: what would make something like this actually worth paying for in your stack? That's the part I'm trying to figure out.

DEV Community: Choi Changhwan

I built free email, phone & card validators + a tiny hosted API (with real MX deliverability)

What it does

Using the API

Honest limitations