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AI Email Subject Line Generator

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Subject lines decide open rate. A 5% bump in opens can mean 30% more replies and conversions downstream. This AI email subject line generator drafts 10+ subject lines per email — tuned for cold outreach, marketing newsletters, transactional emails, and internal updates. No signup, unlimited.

Subject line formulas that open in 2026

Five formulas with proven open-rate lift. (1) Question subjects naming the recipient's situation ('Scaling support past 1,000 tickets?'). (2) Specific number promises ('A 47% lift on your homepage'). (3) Named context ('via [mutual]', 'follow-up to [prior thread]'). (4) Curiosity gap ('The 3 marketing mistakes costing you $10K/month'). (5) Pattern interrupt ('I owe you an apology').

The generator outputs one variant per formula. A/B test the 5 in your next send.

Subject line length: shorter than you think

Mobile clients show 30-50 characters before truncation. 60-70% of email opens happen on mobile. So your subject line has 30-50 characters to do the entire job of getting opened.

Gmail desktop shows more (60-80). But the mobile-first reality means: lead with the most important word, cut filler ('Quick question about...' wastes 4 chars on 'Quick'). The generator caps suggestions at 50 chars by default.

Subject lines to avoid (trigger spam filters)

Words that boost spam scores: 'free', 'guaranteed', 'urgent', 'act now', 'limited time', ALL CAPS, excessive punctuation ('!!!'). Plus tactics modern filters catch: emoji-stuffed subjects, deceptive 're:' or 'fwd:' when not actually a reply/forward, and subjects that don't match the body content.

The generator avoids these. Still test with a deliverability tool (Mail-tester, GlockApps) before high-volume sends.

Tips for getting the most from this tool

Test 5 subject lines per email. Even a 2% open-rate lift compounds.
Mobile truncates at 30-50 chars. Front-load the important word.
Avoid ALL CAPS, excessive '!!!', emoji-stuffing — all spam-filter triggers.
Personalize when you can. '[Name], a 47% lift on your homepage' beats generic.
Don't fake 're:' or 'fwd:' — modern filters catch the deception.

Frequently asked questions

What's the ideal length for an email subject line?

30-50 characters for mobile-first opens. Anything above 50 risks truncation on mobile.

Is the AI email subject generator free?

Yes. Free, no signup, unlimited.

Will AI-generated subject lines trigger spam filters?

Not if you avoid the standard trigger words. The generator filters those by default. Test with Mail-tester before high-volume sends.

How many subject lines should I A/B test?

3-5 variants per send. Email platforms (Mailchimp, ConvertKit, etc.) include native A/B test features that auto-allocate to the winner.

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Every major platform. One dashboard.

Schedule once.
Post everywhere.

One workspace for every channel your audience lives on.

Start free trial Try Live Demo

Please wait while we prepare your content

AI Email Subject Line Generator

Subject line formulas that open in 2026

Subject line length: shorter than you think

Subject lines to avoid (trigger spam filters)

Tips for getting the most from this tool

Frequently asked questions

What's the ideal length for an email subject line?

Is the AI email subject generator free?

Will AI-generated subject lines trigger spam filters?

How many subject lines should I A/B test?

Related free tools

Schedule once.Post everywhere.

Schedule once.Post everywhere.

AI Email Subject Line Generator

Subject line formulas that open in 2026

Subject line length: shorter than you think

Subject lines to avoid (trigger spam filters)

Tips for getting the most from this tool

Frequently asked questions

What's the ideal length for an email subject line?

Is the AI email subject generator free?

Will AI-generated subject lines trigger spam filters?

How many subject lines should I A/B test?

Related free tools

Schedule once.Post everywhere.

Schedule once.Post everywhere.

Schedule once.
Post everywhere.

Schedule once.
Post everywhere.

Schedule once.
Post everywhere.

Schedule once.
Post everywhere.