The preheader is the snippet of preview text most inbox apps show after the subject line. Gmail shows about 90 characters, Outlook 55, Apple Mail 140. A good preheader extends the subject - it does not repeat it.

How long should a preheader be?

Aim for 40-90 characters. Under 30 leaves preview real-estate empty (clients fill it with body text). Over 100 gets truncated on most clients including Gmail.

What does the joint score measure?

Four factors: subject standalone score, preheader length budget, overlap (n-gram redundancy between the two), and complementary framing (does the preheader add new information rather than restate).

📬 Inbox preview

Preheader optimizer

The preheader is the second half of every subject line. Score them together, see the inbox preview, fix overlap before you send.

Live preview Joint score Gmail / Outlook / Apple Mail

Sender (just for the preview)

Subject line

Preheader

Inbox client to mock

Live inbox preview

Sender

Your subject appears here

Your preheader appears here

FAQ

Frequently asked questions

What is a preheader?

The snippet of preview text after the subject. Gmail shows ~90 chars, Outlook ~55, Apple Mail ~140.

Optimal length?

40-90 characters. Under 30 lets the client fill it with body text; over 100 gets truncated.

Should it repeat the subject?

No. It should extend - add the second half of the story, the proof point, or the hook the subject couldn't fit.

Free?

Yes - all client-side.

Understand the methodology

Preheader text: the second half of every subject line

How preheader text functions as a second subject line, the character limits by email client, and the three preheader patterns that consistently lift open rates.

Read the guide →

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