1Pick a scenario
Cold email, sales, follow-up, meeting request or formal business — each has its own proven patterns.
Free cold email subject line generator
Cold email subject lines
Cold email subject lines
that get opened
Generate proven cold email subject lines 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 AICold email subject lines for people who don't know you yet
In a cold email, the subject line is competing with a full inbox from senders the recipient already trusts. You have no existing relationship to lean on, so the line has to earn the open on relevance alone — it should read like a note from a busy colleague, not a campaign blast.
The lines that work are short, lowercase and specific to the prospect's world. Reference their company, role or a problem they actually have, and resist the urge to tease or sell in the subject itself. A line like "quick question about Acme's onboarding" or "idea for your Q3 pipeline" out-opens anything that smells like marketing.
- Name the company or a specific detail you researched.
- Stay under ~40 characters so it reads as personal on mobile.
- Skip "Re:" fakes, ALL CAPS and false urgency that erode trust.
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