This is a representative preview, not a live inbox test. Actual rendering varies by client version, device, settings, personalization, sender reputation, and message markup.
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What does this calculator estimate?
An email preview tester checks how your subject line and sender name display across major clients. Enter the details to see which clients truncate them.
- Tests Gmail, Apple Mail, Outlook, Yahoo
- Compact, wide, and desktop layouts
- Flags truncation before you send
Why preview testing matters
Subject lines and sender names render differently across email clients — the 60 characters that fit in your inbox may truncate in Gmail's compact view. The tester simulates each client's display budget so you can shorten before sending, not after.
Limitations to watch for
Client budgets are estimates and change with UI versions and device widths. The tool checks length, not content quality. Emoji and international characters measure differently than ASCII in some clients.
How to use it in practice
Draft the subject and sender, run the test, and shorten until all key clients fit. Front-load the important words — truncation cuts from the right. Use emoji sparingly; they consume more display width than their character count suggests.
- Enter the subject line and sender name.
- The tool checks each client and layout.
- Shorten until nothing truncates.
What an email preview tester does
The tool renders how an email subject line and preview text appear in common clients — desktop, mobile, and inbox lists — before you send. Subject length, preview text, and the sender name are the three visible elements that decide the open.
Why preview text matters
The preview (snippet) is the second line of your pitch after the subject. Clients truncate it differently — mobile shows fewer characters — so a preview that works on desktop can cut off mid-word on phones. The tester shows the truncation points.
Subject length by client
Most desktop clients show 60–70 characters; mobile shows 30–40. A subject optimized for desktop may hide its payoff on mobile. The tester's client simulation makes the mobile-first subject the default choice.
A worked example
'Your invoice is ready — view and pay now' (39 chars) fits mobile; adding 'plus last month's usage summary' pushes past 60 chars and truncates on phones. The tester flags the cut point so the critical message stays visible.
Beyond the preview
The tester covers the inbox moment; the send experience is deliverability (authentication, spam score, engagement). Use the preview to maximize opens, then test the full send with a real campaign tool.
How this calculator works
Formula
Checks subject lines and sender names against client display budgets (Gmail, Apple Mail, Outlook, Yahoo) in compact, wide, and desktop layouts, flagging likely truncation.
Worked example
A 60-character subject line truncates in Gmail's compact view (34–46 char budget) but may fit on desktop.
Assumptions to verify
- Client display budgets reflect current layouts.
- Character counts are approximate.
- The subject is the first line of the email.
Frequently asked questions
How do I test an email subject line?
Enter it in the tester — the tool simulates each client's display budget and flags truncation.
What is the ideal subject length?
Under ~40 characters for safety on mobile compact views; longer works on desktop.
Why does my subject truncate in Gmail?
Gmail's compact view budgets roughly 34–46 characters for the subject — anything longer gets cut.
Does the sender name count?
Yes — it shares the same display line and eats into the subject's space.
Do emoji affect length?
Yes — they render wider than one character and consume more display space.
What's the difference between layouts?
Compact (mobile), wide (tablet), and desktop clients each allocate different character budgets.
Is this a deliverability test?
No — it's a display test. Deliverability (spam placement) is a separate concern.
What is preview text?
The snippet shown after the subject in most email clients — the second line of your pitch.
How long should a subject be?
30–40 characters for mobile safety; the tester shows each client's truncation.
Does preview text truncate?
Yes — mobile shows fewer characters than desktop; the tester simulates both.
Is this a deliverability tester?
No — it tests the visible inbox presentation; deliverability needs full-send testing.
Cite this tool
BoringToolsKit. “Email Preview Tester.” boringtoolskit.com/email-preview-tester/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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