Score any subject line 0 to 100 and see exactly what helps and what hurts, then preview it live in Gmail and Apple Mail with realistic truncation before you hit send. All in your browser. No signup.
{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.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 →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.
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.
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.
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.
The Pro version previews your full email across Outlook, Gmail, and Apple Mail and recommends the best send time for your audience.
Get early access, book a free call →Type a subject line and the tester scores it from 0 to 100 with a rule-based checklist, not a guess and not an AI model. The score starts at 100 and adds or removes points for character length (about 30 to 50 reads best), word count, spam-trigger words from a built-in list, ALL-CAPS words, heavy punctuation and emoji, and whether you include a personalization token like {first_name} or [City]. Every factor shows up in the breakdown with the exact points it added or subtracted, so the number is never a black box.
Below the score it draws a live inbox list preview for Gmail and Apple Mail, on both mobile and desktop, truncating your sender name, subject, and preheader at realistic character limits for each one. That list view is the part a subscriber actually sees before deciding to open. Everything runs in your browser, so your subject lines and preheader never leave your device. It is one of more than 50 free tools we publish at our tools library with no email wall.
The tool scores the inbox list view, not your email itself. It does not render the HTML body of your message across clients the way paid services like Litmus and Email on Acid do, and it cannot promise a deliverability result or predict your open rate. Use it to tighten the line and catch obvious problems, then A/B test your top two subjects against your real list. Email is one piece of the funnel, which is why we also handle content marketing and the landing page behind the click.
Not on its own. The score rewards subject lines that follow inbox best practices: a clear length, no spam triggers, restrained punctuation, and a real preheader, so they read well and are less likely to be filtered or cut off. It cannot predict your actual open rate, which depends on your list, your sender reputation, and your offer. Treat a strong score as a good starting point, then A/B test your top two against your real audience.
The tester checks your subject against a built-in list of words and phrases that overused promotional email leans on, things like free, act now, guarantee, and urgent, and a separate punctuation check flags rows of dollar signs. It matches whole words and lists every hit alongside the points the check cost. This is a plain heuristic to keep your language specific, not a copy of any provider's real spam filter, so a clean score is not a deliverability guarantee.