GPT for Google Sheets, Docs AI, Slides, Forms
Free tool · Email marketing

AI Email Subject Line Generator

Describe your email and get subject lines with preview text that people actually open. Every line comes with a length check and a mobile inbox preview.

Subject + preview textMobile length check{{first_name}} personalization

Describe your email

Your subject lines

Your subject lines appear here, each with preview text, a character count and basic spam checks.

What makes a subject line get opened

Be specific

“3 fixes for your Q3 report” beats “Quick question”. Say what is inside and who it is for.

Front-load it

Phones cut long subjects, so put the key words first and use preview text for the rest.

Stay honest

No fake “Re:”, no ALL CAPS, no promises the email does not keep. It protects your sender reputation.

Test two subject lines on small parts of your list before the full send, and keep the one that gets more replies, not just more opens.

Personalize every subject line at scale

Mail Merge for Gmail and Sheets sends one email per row of your Google Sheet from your own Gmail, filling merge tags such as {{first_name}} and {{company}}, with open, click, reply and bounce tracking.

Install Mail Merge

FAQ

Is the subject line generator free?

Yes. You can run it twice every 20 minutes in the same browser, with no sign-up; entering your email unlocks five more runs.

How long should an email subject line be?

Short enough to read on a phone. Mobile inboxes often cut subject lines after roughly 30 to 50 characters, depending on the app and screen, so put the most important words first. Each line here shows its character count and a length check.

What is preview text?

Preview text, or preheader, is the short line inboxes show after the subject. Use it to add something the subject does not say, rather than repeating it.

Can I personalize subject lines with the recipient's name?

Yes. Tick Add {{first_name}} and some lines will include that merge tag. Mail Merge for Gmail and Sheets fills it from your Google Sheet for every recipient.

How do I avoid the spam folder?

Avoid ALL CAPS, piles of exclamation marks and pushy phrases such as "act now" or "100% free", and never use a fake "Re:" or "Fwd:". The basic checks on this page flag these. They are not a deliverability guarantee: your sender reputation and list quality matter more.

Which AI model writes the subject lines?

OpenAI's GPT-4o mini, called through the DocGPT.ai API. DocGPT.ai is not affiliated with OpenAI or Google.

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