List Detective: Free Email List Checker

The in-browser processing is a smart move for something handling sensitive email data, no server uploads means no trust gap to overcome. Clean execution for a tool that could have easily felt sketchy otherwise.

The "your list never leaves your device" angle is underrated. Every email marketer I've talked to has done the mental gymnastics of "we're technically leaking our subscriber list to clean it, but the tool promises they'll delete it." Browser-based removes the promise from the equation entirely.Been running my own cold email prep for the last month (9 mailboxes across 3 domains, all warmed) and the pattern I keep seeing: teams verify their list once at import, but a 6-month-old verified list is not a verified list anymore. Emails go stale, roles change, companies fold. The list you cleaned in January is not the list you're sending to in July.To your v2 question, the check I keep wanting is company-level status detection. Not just "is this email valid" but "is this company still active." A valid inbox at a shut-down company still bounces, just with a different error signature. Distinguishing "person left" from "company gone" would be the deliverability signal most tools don't surface.Also the disposable domain check is a category that's evolving faster than most check tools track. New disposable providers spin up weekly. Curious how you handle keeping that list fresh without needing constant manual maintenance.

How does it actually catch things like role-based addresses or temporary inboxes, and is it checking against a maintained blocklist or just syntax rules?

How does it actually catch things like role-based or disposable addresses, and does it check MX records live or just match against a static list?

I`m not an email marketer, but interested in the topic and I really love the way you organised FAQ section on the website - very thoughtful and informative! Congratulations on launch!

Congratulations on the launch! I tried it on your site and like how it works. I find this genuinely useful, especially the GDPR angle since nothing leaves the browser. One question: you mention up to 100k addresses -- does that run comfortably on an average laptop, or is there a point where browser performance starts to degrade?

Being able to flag role-based addresses like info@ or support@ would be a nice addition since those often cause more bounces than personal inboxes.

Calling all curious email marketers! 🕵️

Mumme here, a marketing technologist from Stockholm — and I built List Detective because I kept seeing the same problem: email marketers uploading lists to cleaning tools without realizing they were sending their subscribers' data to a third-party server.

List Detective runs entirely in your browser. Your list never leaves your device — not a single address is sent anywhere. For anyone with compliance obligations — GDPR in particular, that matters.

It checks for invalid formats, role-based addresses (info@, noreply@, admin@), disposable domains, common typos like gmial.com, and suspicious TLDs — up to 100,000 addresses at once, instantly.

Try it with the sample data on the site to see every flag type in action before uploading your own list.

Would love your feedback — especially from email marketers who've run into deliverability issues from dirty lists. What checks would you want to see in v2?