Email Subject Line Tester
Score a subject line before you hit send: length, spam triggers, personalization and specificity, with a live phone-inbox preview and AI rewrites.
- –Length
- –Spam triggers
- –Shouting
- –Personal
- –Specific
- –Emoji
- –Trigger words
Phone inbox preview
Subject lines vs headlines
A subject line competes in an inbox, not a search page. That changes the rules: there is less room (about 35–40 characters on phones), the sender name does half the work of earning trust, and the preheader acts as a second line. What carries over from headlines is specificity: "3 quick wins for your garden" beats "October newsletter" every time.
For blog and web headlines, use the headline analyzer instead; it scores for search results and social feeds.
Questions people ask
What is a good length for an email subject line?
Roughly 30–50 characters. Mobile mail apps typically show around 35–40 characters of the subject, and desktop clients show more. Put the most important words first.
Which words trigger spam filters?
No single word guarantees the spam folder, since modern filters weigh sender reputation and engagement most. But phrases like "free money", "act now", "100% free", "risk-free" and "click here", ALL CAPS and "!!!" are classic red flags that also put readers off.
Does personalization improve open rates?
Using the reader's name or addressing them with "you" can help, especially when the rest of the subject is relevant to them. Personalization in the content matters more than a merge tag alone.
Should I use emoji in subject lines?
One relevant emoji can help a subject stand out in a crowded inbox, but results vary by audience, so test it. Avoid several emoji; that reads as promotional.
What is preheader text?
The preview line shown after the subject in most inboxes. If you don't set it, the email client pulls the first text of the email, which is often "View in browser". Use it to extend the subject's promise.
More tools on the anvil
- Headline AnalyzerScore any headline 0–100 and see exactly what to fix.
- SEO Title CheckerPixel width, Google preview and keyword placement.
- AI Headline GeneratorTen headlines for any topic, tagged by formula.
- Blog Title GeneratorFormula-based blog post title ideas, instantly.
- SEO Title GeneratorKeyword-first titles that fit in 600 pixels.
- YouTube Title GeneratorVideo titles that hook in the first 50 characters.
- Meta Description GeneratorWrite and length-check search snippets.
- Title Case ConverterAP, APA, Chicago, MLA and sentence case.