Free AI Subject Line Generator + 10 Proven Prompt Formulas

Aim for 28–50 characters. This length is optimized for mobile devices, which account for the majority of email opens. Always front-load your most important keywords and your offer.

Yes, but sparingly. One relevant emoji can increase visibility and convey emotion, but overusing them can look spammy. Always test with your audience to see what resonates.

Absolutely. It's a missed opportunity not to use it. A good preheader (35–80 characters) should complement the subject line by adding context, a secondary benefit, or a curiosity hook. Never repeat the subject line.

Start with two (A/B). Testing more than two variants (A/B/C/D) requires a much larger list size to achieve statistical significance. Stick to testing one variable at a time for the clearest results.

Yes. AI can inadvertently use spammy language. Always review suggestions and avoid excessive capitalization, multiple exclamation points, and risky keywords. Run your final choices through a spam-checking tool before sending.