Preview generators
Mobile email inbox preview generator
Test how your sender name, subject line and preheader are cut in a mobile inbox, where roughly 35 characters survive and length decides who reads you.
The Gmail app as it renders today, on an iPhone 17 running iOS 26.
Instructions
How to use this tool
- 01Enter your sender name, subject line, and preview text (preheader).
- 02Watch where the mobile inbox cuts each one: about 35 characters of subject and 45 of preview text in the Gmail app.
- 03Shorten until nothing that matters falls past the cut, and move the payoff to the front.
- 04Review the checks: subject length, preheader usage, and common spam-filter tripwires.
- 05Download the PNG to share the inbox rendering in reviews.
Background
Length is what gets you read
On a phone the whole decision is made on three short strings: sender name, subject, and preview text. Nothing else is visible, and the only variable you fully control is how long each one is.
The budgets are tight and they are what this tool tests. The Gmail app cuts the subject at roughly 35 characters and the preview text at roughly 45, where Gmail on a desktop allows about 70. A subject that survives the phone survives everywhere, which is why this preview is the phone and a desktop preview is a separate thing.
So the rule is length before cleverness: get the payoff into the first 35 characters, and use the preheader to finish the thought rather than repeat it. The sender name still earns the most trust, since people open people they recognise, but a subject cut mid-word costs you the open no matter who sent it.
Background
What the checks look for
The subject checks flag lengths outside the 20 to 50 character sweet spot, all-caps subjects, fake Re: and Fwd: prefixes, and stacked exclamation marks, all of which correlate with spam-folder placement and eroded trust. The preheader check verifies you are actually using the space: an empty preheader means clients pull the first text they find in the body, which is rarely what you would choose.
These are heuristics, not a deliverability score. Inbox placement depends primarily on authentication (SPF, DKIM, DMARC) and sender reputation, which the deliverability tools in this hub cover.
FAQ
Frequently asked questions
How long should an email subject line be?
20 to 50 characters is the reliable range: long enough to say something specific, short enough to survive mobile truncation, which lands around 35 characters in the Gmail app. The essential words belong at the front.
What is a preheader?
The snippet of text email clients show after the subject in the list view, pulled from a hidden preheader element or the first text in your body. Treat it as a second subject line that completes the first rather than repeating it.
Do emoji in subject lines help or hurt?
Measured effects are mixed and audience-dependent: an emoji can lift visibility in a plain inbox but reads as promotional in others, and some clients render them inconsistently. Test with your own list rather than assuming.
Does this tool test spam filtering or deliverability?
No. It previews rendering and flags copy-level red flags. Actual inbox placement is governed by SPF, DKIM, DMARC, and sender reputation; use the DMARC, SPF, and DKIM checkers in this hub for that layer.
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