Subject Line Tester

A good email subject line is usually 30 to 50 characters, or roughly four to nine words. That length shows in full on most desktop inboxes, and mobile apps typically display only the first 30 to 40 characters, so put the most important words first. Very short subjects can work, but they need to be specific.

Spam words can hurt, but rarely on their own. Modern filters weigh your sender reputation, authentication and engagement more heavily than any single word. Phrases like "act now" or "100% free" add risk, though, especially combined with capitals, exclamation marks or a new domain. Plain, specific wording is the safer choice.

One emoji can help a marketing email stand out, especially to an audience that already knows your brand. Avoid them in cold outreach and formal business email, where they can look promotional. Never use several, since they render differently across email clients and can push your email toward the Promotions tab.

A good cold email subject line is short, specific and looks like it came from a person, not a marketing team. Mention something relevant to the reader, such as their company or a problem they likely have, and skip hype, capitals and fake "Re:" prefixes. Lowercase, conversational subjects of three to six words often work well.

The subject line tester starts at 100 and deducts points for problems: a subject that is too short or too long, spam trigger phrases, words in capitals, repeated punctuation, fake "Re:" or "Fwd:" prefixes, and several emoji. It also flags missing personalization and preview text. Everything runs in your browser.