Open an inbox on your phone and look at what's actually visible before you tap anything: a sender name, a subject line, and one line of grey preview text. That preview text — also called preheader text — is some of the highest-leverage real estate in email marketing, and an enormous number of campaigns waste it on autopilot filler.
The most common mistake, by far
If you've ever built an email in a template builder without touching the preheader, there's a good chance your preview text currently reads something like "View this email in your browser" or "Having trouble viewing this email?" — leftover boilerplate that adds zero persuasive value. It's the equivalent of a billboard that says "this is a billboard."
Subject line and preview text are one unit
The subject line and preview text render together, right next to each other, and readers process them as a single unit before deciding whether to open. That means they should work as a pair — not repeat each other. If your subject says "Your cart is about to expire" and your preview text says "Don't miss out — your cart is expiring soon!", you've said the same thing twice and wasted the second slot.
What good preview text does instead
- Adds new information. A specific detail, a number, an unexpected benefit the subject didn't mention.
- Opens a curiosity gap. A question or a hint of something worth finding out.
- States a concrete benefit. Not "check this out" — "save 10% before midnight."
Length matters more than people think
Different clients truncate at different points. As a rough, illustrative guide: Gmail's mobile app shows roughly the first ~38 characters of a subject and ~40 of preview text. Apple Mail on iPhone shows a bit less subject but can wrap preview text across two lines, giving you closer to ~90 characters. Outlook's desktop reading pane is the most generous, often showing ~60 characters of subject and ~130 of preview. These are not pixel-exact guarantees — font size, sender name length, and user settings all shift the cutoff — but they're close enough to plan around: front-load your point in the first 40 characters of preview text, because that's the part almost everyone sees no matter the client.
A simple before/after
Before: Subject — "Sale This Weekend"; Preview — "View this email in your browser." After: Subject — "Sale This Weekend"; Preview — "20% off ends Sunday at midnight — no code needed." Same subject, completely different preview — one wastes the slot, one closes the loop.
How to check your own pairing
Read your subject and preview text together, out loud, as a reader would see them. Ask three questions: Does the preview repeat the subject, or add something new? Is there a filler phrase in there by accident? Is there any number, question, or clear benefit anywhere in the pair? If the answer to any of those is a problem, you have a five-minute fix that could measurably move your open rate.
Frequently Asked Questions
Yes — the Email Preview Text & Subject Line Optimizer simulates Gmail (mobile), Apple Mail (iPhone), and Outlook (desktop) previews at realistic, illustrative truncation lengths, and scores your subject/preview pairing for common mistakes. It's a one-time $4.99 purchase — no subscription, no account required.
Because it's generic filler that adds no persuasive value in a slot readers actually see before opening. The tool checks your preview text against a list of common filler phrases and flags them so you can replace them with a real hook or benefit statement.
No — they're illustrative ranges, not pixel-exact guarantees. Actual truncation varies by device, font size, sender name length, and individual client settings. Treat the previews as a realistic approximation, not a precise spec.
The 0-100 score combines five checks: whether the preview text is generic filler, how much the preview text overlaps/repeats the subject line, whether subject and preview lengths fall in practical visibility ranges, and whether there's a curiosity gap or benefit signal (a number, a question, or benefit language) present.
No — it's a fully offline, local simulation. It doesn't connect to Mailchimp, Klaviyo, or any ESP, and it doesn't send anything. You type your subject and preview text, and everything is calculated in your browser.