1Pick a scenario
Cold email, sales, follow-up, meeting request or formal business — each has its own proven patterns.
Free email subject line generator & tester
Email subject lines
Email subject lines
that get opened.
Generate proven email subject lines for any scenario, and score your own for length, spam triggers and open-rate killers — instantly. Free, no sign-up.
No sign-up required
Spam-word check
Instant scoring
A great subject line is wasted on the wrong list.
Flow AI finds your ideal buyers and runs personalised email and LinkedIn outreach on autopilot — with built-in daily limits and human-like pacing that protect your domain and reputation.
Start free in Flow AIWriting subject lines that get opened
The subject line is the only part of your email most people read before deciding to open, archive or delete. A few words carry the entire weight of whether your message is seen at all.
Keep it short, specific and honest. Promise something the email actually delivers, write the way a real person would, and skip the gimmicks that get filtered or ignored.
- Lead with relevance, not your own pitch.
- Aim for under 50 characters so it survives mobile previews.
- Avoid spammy caps, exclamation marks and money words.
Better subject lines in seconds
The subject line decides whether your email gets opened or ignored. Get it right.
2Generate & tweak
Add what it's about and get a set of options, each scored for length and deliverability. Copy your favourite.
3Test your own
Paste any subject line to grade it instantly — length, word count, spam triggers, caps and punctuation.
What makes a subject line work
Short & mobile-first
Most inboxes cut off around 50–60 characters. Lead with the part that earns the open.
Specific, not salesy
Spam-trigger words and ALL-CAPS hurt both opens and deliverability. The tester flags them for you.
Curiosity + relevance
The best lines hint at something useful and specific to the reader, without giving everything away.
Frequently asked questions
Win the open. Then let Flow AI win the reply.
No credit card required