Email Subject Line Tester

The sweet spot is 30–50 characters. Mobile email clients (which now account for 60–70% of opens) truncate subject lines at around 33–40 characters. Desktop clients like Gmail and Outlook show 60–70 characters. Keeping subjects under 50 characters ensures the full line is visible on every device. Very short subjects (under 20 characters) can work for transactional or personal-feeling emails, but risk being too vague for promotional sends.

Preheader text (also called preview text) is the short summary line that appears after the subject line in most email clients. It's your second chance to earn the open. If you don't set it explicitly in your email code, the client will pull the first text it finds in your email body - often something unhelpful like "View this email in your browser." A good preheader extends or complements the subject line rather than repeating it, ideally 40–90 characters.

Common spam trigger words include: FREE, GUARANTEED, WINNER, CONGRATULATIONS, ACT NOW, CLICK HERE, CASH, PRIZE, NO COST, BUY NOW, URGENT, EARN MONEY, RISK-FREE, 100%, LIMITED TIME OFFER, and phrases like "you've been selected" or "double your." Modern spam filters use machine learning and look at the full email (sender reputation, HTML structure, engagement history), but flagged subject lines are still a fast path to the junk folder. Avoid all-caps, excessive punctuation (!!!), and dollar signs ($$$).

It depends on your audience and context. Studies show emojis can lift open rates 10–15% when used sparingly and appropriately - one emoji at the start or end of a subject line tends to perform best. Emojis work well for B2C e-commerce and consumer brands. They tend to underperform or feel off-brand for B2B, financial, medical, or professional services audiences. Never use emojis as a substitute for a compelling subject line - they should enhance it, not rescue it.

Industry averages vary widely by sector. E-commerce typically sees 15–25% open rates. SaaS and B2B companies often see 20–30%. Newsletters with highly engaged audiences can hit 35–50%. The most important benchmark is your own historical average - a subject line that beats your list average is a win. Open rates have become less reliable as a standalone metric since Apple's Mail Privacy Protection (MPP) inflates open rates for Apple Mail users. Look at click rate and revenue per email alongside opens.