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Free AI email subject line generator

There’s a faster way to create subject lines that get you the opens. Omnisend’s free AI subject line generator writes high-converting lines in seconds.

Tone:

Friendly
Urgent
Professional
Curious

Suggested subject lines

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Give our AI about 20 seconds to generate the subject lines for you.

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What is an AI subject line generator?

An AI subject line generator is a tool that writes email subject lines for you. Type in a few keywords about your campaign, pick a tone, and you’ll get several options to use as is, edit, or A/B test. Omnisend’s generator is free and works for all kinds of campaigns, from welcome emails to sale announcements.

How to use the AI subject line generator

1
Enter your email details

Add at least five keywords and a short idea of what the email is about. Mention the campaign type and who it’s for.
2
Generate your options

Pick a tone and click Generate subject lines. You’ll get several options in seconds, and you can ask for a couple more.
3
Review and A/B test before you commit

Edit the lines you like so they sound like your brand. Then test your top two against each other and send the winner.

What makes a good
subject line

Four things to check before you hit send, whichever line you pick.

Length

Keep it short enough for a phone

Phones show fewer characters than desktop inboxes, so long subject lines get cut off. Put the offer or most important word first, and aim for about 30–40 characters.

Personalization

Make it personal

Adding someone’s first name, a product they recently viewed, or their city shows the email was written with them in mind. Just check how the line reads when that data is missing.

Urgency

Create urgency without sounding like spam

A real deadline, like “Ends tonight,” gets attention. All caps, rows of exclamation marks, and phrases like “100% free” or “act now” make an email look like spam to readers and filters.

Emojis

Use emojis on purpose

One emoji can help your subject line stand out in a busy inbox. Use it to support a word, not replace it, and preview how it looks on different devices.

Tips for getting better results from the generator

1
Be specific with your input

“Summer sale, 20% off sandals, ends Sunday” gets better lines than “sale email.” Include the offer, the product, and any deadline.
2
Pick a tone

Choose friendly, urgent, professional, or curious tone so the lines match the mood of the campaign.
3
Mention your audience

Loyal customers and new subscribers respond to different things. Say who the email is for, like “first-time buyers” or “VIP customers.”
4
Treat the output as a draft

Use the lines as a starting point and edit them so they sound like your brand.
5
Pair it with the subject line tester

Run your favorites through the subject line tester to check length, wording, and scannability before you send.

Why you should use an AI subject line generator

The first (and sometimes only) thing people see

Nearly half of email recipients (43%) decide whether to open an email based on the subject line alone. And 69% report emails as spam based on the subject line, too.

Scale without the bottleneck

When you’re juggling regular campaigns, seasonal sales, and automated flows, you can’t spend an hour on every subject line. Our AI generator gives you solid starting points, so you can keep up with your sending schedule.

Beat writer’s block

Our AI subject line generator lets you get the first lines faster. Writers and email marketers can use this tool to focus on perfecting rather than drafting.

Built-in variety for A/B testing

Get several subject lines at once and test them against each other to find your winner. Less time writing options means more time learning what your audience actually opens.

Resources

Keep learning

100 best email subject lines for sales in 2026

Blog

100 best email subject lines for sales in 2026

100+ welcome email subject lines

Blog

100+ welcome email subject lines

Subject line tester

Free Tools

Subject line tester

Better subject lines start in Omnisend

Get AI subject line suggestions right in Omnisend’s campaign editor, even on the free plan. A/B test your favorites, and let Campaign Booster resend to anyone who didn’t open.

Start free

FAQ

How long should an email subject line be?

Aim for about 30–40 characters, or roughly 6–10 words. Phones show fewer characters than desktop inboxes, so put the offer or the key word near the start. A clear 40-character line still beats a short one that doesn’t say what’s inside.

How many subject lines should I A/B test?

Start with two versions that differ in one thing, like length or tone, so you know what made the difference. Test more only if your list is big enough to give each version a reliable result. The A/B testing calculator shows whether the gap between them is statistically significant.

Can I use emojis in subject lines?

Yes. An emoji can help a subject line stand out, especially in sales and seasonal campaigns. Stick to one or two, put them next to the word they support, and preview the email on a few devices, since some emojis look different from one email app to the next.

How do I avoid spam filters with my subject line?

Write the way you’d write to a customer you know. Skip all caps, rows of exclamation marks, and phrases like “100% free” or “act now.” Make sure the subject line matches what’s inside the email, and send only to people who signed up. Your sender reputation matters as much as the words.

What makes a good ecommerce subject line?

It tells shoppers what’s in it for them: the product, the offer, or the deadline. Good ecommerce subject lines are specific (“Your cart is saved: 10% off ends tonight”), match the email’s content, and fit the type of email, like a welcome email, cart reminder, or seasonal sale.

Is the Omnisend subject line generator free?

Yes. The subject line generator is free, and you don’t need to sign up or share an email address to use it. We don’t store what you type into the generator. Copy the lines you like into any email platform, or send them with Omnisend.

Can I use the generator inside Omnisend?

Yes. Omnisend includes a subject line generator in campaigns on every plan, including the free plan. It suggests options based on your campaign, and you can refine them by tone, length, or language before you send.

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