Free Email Subject Line Tester

Subject line

0 characters

Sender name (optional)

Preheader text (optional)

0 characters

Tip: include a personalization token like {first_name} or [City] to see how it scores. The preview shows the token literally, the way most ESPs display an unfilled merge tag in a draft.

Type a subject line above to get an instant 0 to 100 score, a full breakdown of what helped and hurt, and a live Gmail and Apple Mail inbox preview.

0OUT OF 100

Score

Scores the inbox list view only.

What helped and what hurt

Live inbox preview

This is the list view a subscriber sees before opening. It does not render your email body. Realistic truncation per client and width.

GmailMobile

Apple MailiPhone

Make it stronger

Want emails that actually get opened?

The subject line is step one. We build the whole funnel, from the email to the landing page that turns the click into a booked job. Get a free mockup or audit.

Get a free mockup or audit →

The subject line is the only line that matters until it gets opened

A perfect email is worth nothing if nobody opens it. The subject line and preheader are the entire pitch a subscriber sees in their inbox list. This tester scores yours against the factors that actually drive opens, then shows you exactly how it will look in Gmail and Apple Mail before you send.

How the score works

The score is rule-based, not a guess. It starts at 100 and adjusts for character length (about 30 to 50 characters reads best), word count, spam-trigger words (things like free, act now, guarantee, $$$, urgent), ALL-CAPS words, excessive punctuation and emoji, and whether you use a personalization token. Every factor is shown in the breakdown with the exact points it added or removed, so you always know why you got the number you got.

Why the inbox preview is honest about its limits

Paid tools like Litmus and Email on Acid (which run 74 to 500 dollars a month) do full client rendering of your email body across dozens of apps. This tool does not pretend to do that. It previews the inbox LIST view: sender, subject, and preheader, truncated at realistic character limits for Gmail on mobile and desktop and for Apple Mail. That list view is where the open decision happens, and getting it right is free here.

Why not just use CoSchedule?

CoSchedule has a popular subject line tester, but it forces a signup before you can use it. Ours is instant, runs entirely in your browser, and never sends your subject lines to a server. You get a transparent score plus an accurate inbox preview with no email gate.

Pro tips

Aim for roughly 30 to 50 characters so the whole subject survives a mobile inbox.
Front-load the value. Most clients truncate, so put the hook in the first few words.
Write a real preheader. If you leave it blank, inboxes pull the first line of your email, which is often a broken link or a logo alt text.
Use a personalization token (first name, city, or service) when it genuinely fits, not as a gimmick.
Avoid spam triggers, ALL CAPS, and emoji walls. They cost you both score and deliverability.
Test two or three variants here, then A/B test the top two with your real list.

Frequently asked questions

How is the subject line score calculated?

The score starts at 100 and adjusts based on rule-based factors: character length (around 30 to 50 is ideal), word count, spam-trigger words, ALL-CAPS words, excessive punctuation and emoji, and whether you use a personalization token. Each factor shows you exactly what helped and what hurt, so nothing is a black box.

What is the best length for an email subject line?

Around 30 to 50 characters is the sweet spot. That length reads clearly in mobile inboxes, where most opens happen, and avoids the truncation that cuts off your message. Very short subjects can feel vague and very long ones get clipped, so this tester flags both.

Does this tool render my full email?

No, and we are honest about that. This tool scores and previews the inbox LIST view only: the sender name, the subject line, and the preheader as a subscriber sees them before opening. It does not render the HTML body of your email. Paid tools like Litmus and Email on Acid do full client rendering.

Why does my subject look different in Gmail versus Apple Mail?

Each inbox shows a different number of characters before it truncates, and the widths change between mobile and desktop. Apple Mail typically shows more of the subject and preheader than Gmail on mobile. The live preview here mirrors those realistic limits so you can see where your words get cut.

Is the Email Subject Line Tester free?

Yes. It is completely free with no signup and no account. Everything runs in your browser, so your subject lines never leave your device. CoSchedule forces a signup to use theirs, and we do not.

Email subject line tester.