Free & unlimited

Email Subject Line Checker

Length, spam-word scan, and an inbox preview for Gmail & Outlook.

From / Sender name

Subject Line0 characters

Preview Text (optional)0 characters

Length by client

Gmail (desktop)0 / 70

Gmail (mobile)0 / 33

Outlook (desktop)0 / 60

Outlook (mobile)0 / 38

Apple Mail (iPhone)0 / 40

Spam-trigger scan

Type a subject line to scan it.

Inbox preview

GmailDesktop

Your Brand2:14 PM

Your subject line will appear here

OutlookDesktop

Your Brand2:14 PM

Your subject line will appear here

Why subject line length and wording matter

Every email client truncates subject lines at a different point — Gmail desktop shows roughly 70 characters, Gmail on mobile cuts off around 33, and Apple Mail on an iPhone is tighter still. Write past those limits and your carefully-crafted hook gets chopped mid-sentence.

Certain words and patterns also correlate with spam-filter flags and promotions-tab sorting — not a guarantee either way, but worth knowing before you send.

How to use this tool

1Type your subject line — the length checker updates for each major email client instantly.

2Add your preview text (preheader) to see how it pairs with the subject in the inbox preview.

3Check the spam-trigger scan for flagged words, excess exclamation marks, or ALL-CAPS words.

4Adjust and re-check until the preview reads cleanly on both Gmail and Outlook.

Why this matters for deliverability

A truncated subject line often loses the exact word that would have earned the open
Spam-trigger words don't auto-block an email, but they add up with other signals filters weigh
Preview text is free real estate — an empty one lets the client show a chunk of your email body instead

FAQ

Will one spam-trigger word get my email blocked?

Almost never on its own. Spam filters weigh dozens of signals — sender reputation, authentication, engagement history — wording is just one input among many.

Why does Gmail show a different length on desktop vs mobile?

Mobile screens are narrower, so Gmail's app truncates subject lines much sooner than the desktop web client does.

What's a good preview text length?

Aim for 40–90 characters that complement (not repeat) your subject line — it's the second thing a recipient reads before deciding to open.

Does this tool store what I type?

No. Everything runs in your browser — nothing is sent to or saved on our servers.