Subject Line Checker

About

Subject Line Checker — See how your email will look in the inbox, before you send

Most email marketers send test emails to check how their subject line looks on different devices. Then they check their phone. Then desktop. Then a different app. Oops, too long. Fix and start over.

This extension gets rid of that silly process.

Subject Line Checker shows you exactly how your subject line and preview text will appear across the major email clients — Gmail, Apple Mail, Outlook, and Yahoo — before you hit send. No more truncated surprises landing in your subscribers' inboxes.

What it does is super simple:
Type your subject line and preview text directly in the extension, or select any text on any page and it auto-fills. Instantly you'll see a realistic inbox preview for each email client and device, plus a clear status for each one:
✓ Fits — you're good to go
⚠ Risky — it might get cut on some devices
✕ Truncated — it will definitely be cut

Covers Gmail (mobile + desktop), Apple Mail (mobile + desktop), Outlook (mobile + desktop), and Yahoo Mail (mobile).

Who it's for:
Email marketers, newsletter writers, sales people, business owners, and anyone who sends campaigns and cares about how their emails look in the inbox. If you send more than a handful of emails per month, this will save you time every single week.

Couldn't be easier to use:
1. Click the extension icon in your browser toolbar
2. Enter your sender name, subject line, and preview text
3. See the results instantly across all supported clients
4. Fix anything that's risky or truncated before sending

You can also select text on any page before opening the extension and it will auto-fill — useful when you're writing directly in your ESP.

Free. No need to create an account. Works anywhere in the browser.

Built by an email marketing professional who got tired of sending himself test emails to a Huawei just to check if the subject line fit.