SubjectLines

Inbox Preview Tool — Subject Line + Preheader, Rendered

Who this is for: For senders who learned the hard way that the inbox list is an advertisement for the email — and that 'view as recipient' only exists after sending.

Subject + preheader rendered as Gmail desktop, Gmail mobile and Outlook will show them — before you send.

Quick answer: The inbox reads as one line: subject (Gmail web ~70 chars, mobile ~35, Outlook ~45) + preheader snippet. Set a deliberate preheader — an unset one lets clients grab 'View in browser' — and preview the compound before sending.

Gmail · desktop
ACME
Your fall guide is here
12 rooms, 3 budgets, one weekend — plus the paint math
Gmail · mobile
ACME
Your fall guide is here
12 rooms, 3 budgets, one weekend — plus the
Outlook · desktop
ACME
Your fall guide is here
12 rooms, 3 budgets, one
Compound rule: the subject makes the claim (26–50 chars), the preheader adds the proof (~40–90 chars) — they read as one sentence in every inbox. An unset preheader lets clients grab body text, which is how “View this email in your browser” becomes your second line.

Sender name renders above the subject in every client — a recognizable name is the one line you never have to write twice. Cuts are approximations; the shapes are the norm.

Core facts
Three rowsSender · subject · preheader — rendered per client
CutsGmail web 70+100 · Gmail mobile 35+45 · Outlook 45+30
Preheader HTMLhidden div, display:none, right after <body>
Classic waste'View this email in your browser' as your snippet
Compound ruleSubject = claim, preheader = proof (~40–90 chars)
StatusRules follow public email-marketing benchmark practice (2026): ~35–70 visible characters by client, 175-word spam trigger list, sentence case, one clear idea per line. Client truncation figures are engineering approximations — devices, fonts and zoom shift them.

What does my email look like in the inbox?

The inbox shows three stacked parts: sender name, subject line, and preheader text — the snippet pulled from the first body copy when no preheader is set. Each client truncates differently: Gmail desktop shows ~70 characters of subject then ~100 of preheader; Gmail mobile ~35 then ~45; Outlook desktop ~45 then a short snippet. The preview renders your subject + preheader in all three so you can check the compound sentence a subscriber actually reads. The classic failure: a strong subject ('Your fall guide is here') followed by an auto-generated preheader ('View this email in your browser') that wastes the second line. Set the preheader deliberately — it's 40–100 free characters of persuasion most senders leave to chance.

Common uses

  • Checking the subject + preheader compound read before sending
  • Stopping the 'View in browser' preheader from wasting the snippet
  • Deciding what to front-load vs what can truncate
  • Reviewing mobile-first lists where the 35-char cut is the norm

Frequently Asked Questions

What is an email preheader?
The summary text after the subject line in the inbox — either the hidden HTML element you set, or the first words of your email body when you don't. Gmail desktop shows ~100 characters of it, Gmail mobile ~45, Outlook ~30. Set it deliberately: it's the second line of your pitch.
How do I set a custom preheader?
Add a hidden div right after the <body> tag: <div style="display:none; max-height:0; overflow:hidden;">Your preheader text</div> — placed before any visible content so the client grabs it first. Then preview it here to see where it truncates alongside your subject.
Why does my preheader show 'View this email in your browser'?
Because that link is the first text in your HTML — most templates put it there. Every subscriber sees it as your snippet and nobody clicks it from the inbox. Either move it below your real content or hide it and set a deliberate preheader.
Do all clients show the preheader?
Most do — Gmail, Apple Mail, Outlook, Yahoo — but lengths vary and a few webmail layouts hide it when the subject is long. The preview shows the three common shapes; treat them as the norm, not a guarantee.
How long should subject + preheader be together?
Think one compound sentence: subject makes the claim (26–50 chars), preheader adds the proof or the offer (~40–90 chars). Together they should read naturally when concatenated — because in the inbox, they always are.

More guides

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Newsletter Subject Lines

Subject line plays for newsletters specifically — habit, naming conventions, issue numbering, and 12 scored examples.

How to Write Email Subject Lines

The seven-step process for writing subject lines that get opened — draft, check, trim, preview — with the ten checks that matter in 2026.

More Deliverability checkers

Spam Word Checker

Scan your subject line against 175 spam trigger words — high-risk and medium-risk flagged, with fixes.

Subject Line Length Analyzer

See exactly where Gmail, Outlook, Yahoo and Apple Mail cut your line — and the character band that fits.

A/B Subject Line Comparer

Two lines side by side — scores, check-by-check differences, and the verdict on which to send.