How the score works
The grader checks your subject line against the same fundamentals that affect real inbox performance: whether it fits on a mobile screen, whether it trips common spam filters, and whether it reads like it was written for a person or a bot. It is a diagnostic, not a promise. No tool can predict your actual open rate, since that depends on your list, sender reputation, and audience, not the subject line text alone.
It works in both English and Romanian. The tool detects which language you're writing in automatically, based on diacritics and common words, and switches its spam-word list and personalization check accordingly. If it guesses wrong, or you're testing a subject line with mixed language, use the language buttons above the input to force it.
| Check | What it looks for |
|---|---|
| Length | 30-50 characters, so it doesn't truncate on mobile |
| Spam trigger words | Wording that inbox filters commonly flag |
| Capitalization | ALL CAPS reads as shouting and hurts deliverability |
| Punctuation | Excess "!" or "?" is a common spam signal |
| Personalization | Merge tags or direct address ("you," "your") |
| Emoji use | One can help it stand out; several look automated |
Common mistakes this catches
- Front-loading the brand name. "YourBrand: New Arrivals Are Here" wastes the first, most-visible characters on something the recipient already knows from the sender field.
- Stacking urgency and discount language. "URGENT!! 50% OFF TODAY ONLY!!!" trips multiple spam signals at once and reads as desperate rather than exciting.
- No differentiation from yesterday's email. If every subject line follows the identical template, engaged subscribers start pattern-matching and skipping without reading.
What this tool can't tell you
It can't tell you if the subject line is actually relevant to your specific list, and it can't replace a real A/B test on your own audience. Use it as a first pass, to catch obvious deliverability and readability issues, before a subject line goes into your actual testing calendar. For the full framework on running tests that produce a trustworthy answer, not just a number, see our guide on A/B testing subject lines.
Frequently asked questions
Is this free?
Yes, no limit on uses, no signup, no email required.
Does my subject line get sent to a server?
No. The scoring runs entirely in your browser using JavaScript. Nothing you type is transmitted, stored, or logged anywhere, including by us.
What's a good length?
Roughly 30-50 characters keeps the full subject visible across both mobile and desktop inboxes. Under 20 characters often lacks context; over 60 typically gets truncated on mobile.