Email Subject Line Tester
Let AI write your outreach emails
MentionAgent crafts personalized outreach emails that actually get replies, so you can focus on your product.
Start Getting Mentioned For $99/moHow scores are calculated
Each subject line is scored across 7 criteria, weighted by impact on open rates. For real-world examples, see our meeting request email subject lines, our guest post pitch templates, or our cold email campaign guide.
| Criterion | Max Points | What it measures |
|---|---|---|
| Word Count | 20 | Optimal length of 6–10 words for highest open rates |
| Character Length | 15 | 30–50 characters ensures full display on mobile |
| Personalization | 15 | Merge tags like {name} or {company} boost opens 20–30% |
| Power Words | 15 | Curiosity and value-driven words that compel opens |
| Spam Triggers | 15 | Words and patterns that hurt deliverability |
| Numbers | 10 | Specific figures add credibility and specificity |
| Formatting | 10 | Proper capitalization and punctuation |
Frequently asked questions
What makes a good outreach email subject line?
Good outreach subject lines are 6–10 words long, include personalization (like the recipient's name or company), use curiosity or value-driven language, avoid spam trigger words, and include specific numbers when relevant.
How long should an email subject line be?
Research shows 6–10 words or 30–50 characters is optimal. This length conveys enough context while fitting fully on mobile screens. Subject lines over 60 characters often get truncated.
Do personalized subject lines get more opens?
Yes. Personalized subject lines that include the recipient's name, company, or a specific reference can increase open rates by 20–30% compared to generic subjects.
What words trigger spam filters in subject lines?
Common spam triggers include "free", "guaranteed", "act now", "limited time", "buy now", "click here", "winner", and "congratulations". Excessive punctuation (!!!) and ALL CAPS also increase spam risk. Email marketing platforms often have built-in spam checks, but for cold outreach you need a separate tool like this one.