Free Email Subject Line Tester

Score your subject line in seconds before you hit send. Check length, power words, spam triggers and emojis, and get clear tips to lift your open rates.

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Inbox preview
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Subject score
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Type a subject line to get your score and suggestions.

  • LengthType a subject line to begin.

Pro tip. Most inboxes cut the subject line around 35 to 40 characters on mobile, so front-load the words that matter. Lead with the value or a hint of curiosity, and keep one clear idea per line.

How to test an email subject line in 3 steps

Check and improve your subject line in under a minute, so more of your list opens the email and your campaign starts strong.

  1. 01

    Type your subject line

    Paste or write the email subject line you are planning to send to your list or your prospects.

  2. 02

    See your score and checks

    The tool scores your line instantly and flags length, power words, spam triggers, emojis and formatting issues.

  3. 03

    Refine and re-test

    Apply the suggestions, tweak the wording, and watch the score climb as your subject line gets stronger.

Why your subject line matters

The subject line decides whether your email gets opened at all. No matter how good the content or offer inside, a weak subject line means most of your list never sees it. Small tweaks here can lift opens across every campaign.

Win the open

Opens are the first conversion in any email. A sharper subject line means more of your list actually reads what you sent.

Avoid the spam folder

Spammy words and shouting caps can hurt deliverability. The tester flags them so your email lands in the inbox, not the junk folder.

Fit every inbox

A length check and live inbox preview show how your line looks on mobile and desktop, so the key words never get cut off.

Free, instant, private

No signup and no AI. Test as many lines as you like, and your subject lines never leave your browser.

Where teams use the subject line tester

From newsletters to cold outreach, here is how marketers and founders use a quick subject line check to lift opens across every kind of email they send.

Email newsletters

Test the subject before each send so your regular readers keep opening and your list stays engaged over time.

Cold outreach

Sharpen sales and prospecting subject lines so they get opened and avoid the spam folder on the first touch.

Welcome and onboarding

Make the first emails new subscribers receive impossible to ignore, setting the tone for everything that follows.

Promotions and launches

Lift opens on sales, launches and limited offers, where every extra open can mean real revenue from the same list.

Abandoned cart emails

Win back shoppers with subject lines that feel timely and helpful, not pushy, so they come back to finish the order.

A/B testing variants

Quickly score two or three subject line options before you send, then test the strongest pair against your list.

FAQs

An email subject line tester is a free tool that scores your subject line before you send it. It checks length, word count, use of power words, spam trigger words, emojis, personalization and other factors that affect open rates, then gives you a score and clear suggestions to improve it.
A common sweet spot is around 30 to 50 characters, or about 6 to 9 words. That keeps the full line visible on most desktop and mobile inboxes. Mobile clients often cut off after roughly 35 to 40 characters, so front-load the most important words. This tester flags lines that are too long or too short.
Keep the subject line short and specific, lead with the value or curiosity, add a power word or a number, and avoid spammy phrases like free money or act now in all caps. Personalization and clear relevance help too. Testing the line here before you send catches the most common issues that hurt opens.
Words and phrases like free, guarantee, act now, risk-free, winner, cash, urgent and excessive punctuation or all caps can raise spam scores, especially when stacked together. A few are usually fine, but several in one line can hurt deliverability. The tester highlights common spam trigger words so you can ease off where needed.
Emojis can help a subject line stand out and lift opens when they fit your brand and audience, but one is usually plenty. Too many can look spammy and may render differently across email clients. The tester notes when you are using emojis so you can keep them intentional.
Around 6 to 9 words tends to perform well, giving enough room to be specific without getting cut off. Very short lines can work for curiosity, while very long ones risk being truncated on mobile. The tool counts your words and characters live as you type.
Yes. The email subject line tester is 100% free with no signup and no limits. Test as many subject lines as you like, for newsletters, campaigns, cold outreach or product emails, without paying anything.
No. The tool runs entirely in your browser using JavaScript and built-in word lists. Your subject lines are never uploaded and never leave your device, so you can safely test unpublished campaigns.

Send your opens to a landing page that converts

A great subject line earns the open, but the landing page earns the customer. Use LanderLab to ship a fast, mobile-friendly page in minutes and turn email clicks into results.

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