Email Subject Line Tester

No – they’re a heuristic list (FREE, BUY NOW, URGENT, DEAL, SAVE, DISCOUNT, etc.). Real email-provider spam filters use much more context: sender reputation, link reputation, content vs subject mismatch, recipient engagement history. Words like “deal” and “save” are flagged here but are common in legitimate promotional emails and aren’t automatically disqualifying. Treat the warnings as “worth a second look”, not as definitive verdicts.

Effectiveness is a numeric 0-100 score that combines length, spam risk, and word count into a single number. Engagement is a discrete label (Low / Medium / High) based on length and emoji usage. They overlap deliberately – high-effectiveness lines usually map to high engagement – but they exist separately so you can tell the difference between “low because the line is risky” (effectiveness drops) and “low because the line is too short or too long” (engagement drops).

These are approximations of common inbox-list truncation. iPhone Mail in portrait shows roughly 35-45 characters; Gmail on mobile shows around 30-40. Desktop Gmail and Outlook tend to show 60-70 characters of subject before truncating with “…”. The 40 / 70 numbers are deliberate round figures – different mail apps and screen sizes vary by ±5 characters or so.

By regex over common emoji Unicode blocks: 1F600-1F64F (faces), 1F300-1F5FF (symbols), 1F680-1F6FF (transport), 2600-26FF (misc), 2700-27BF (dingbats), 1F900-1F9FF (supplemental). Compound emojis built with ZWJ (zero-width joiner) – like 👨‍👩‍👧 – count by their components, not as one glyph. That’s a known limitation of pure-regex emoji counting; if you need exact grapheme cluster counts, use the browser’s Intl.Segmenter.

No. Subject lines are one signal of many – your sender domain’s SPF/DKIM/DMARC status, your IP reputation, your historical engagement rate with the recipient, and the email body all matter at least as much. A perfect-score subject from a fresh, unauthenticated domain still gets binned; a mediocre subject from a well-warmed domain with engaged recipients usually delivers. Treat this tool as a copywriting aid, not a deliverability oracle.

Yes, three. (1) The HTML title had a missing em-dash so “Free Email Subject Line Tester Spam Checker” had two spaces instead of an “-“. (2) The preview headers showed mojibake characters like =� because original emoji (📱) got mangled during file encoding conversion. (3) The recommendations box CSS had border-left: 4px solid: #10b981 with an invalid colon after “solid”, silently dropping the left accent. All three are fixed in this version.

No. The page loads three static files (HTML, CSS, JS) and then runs entirely in your browser. You can disconnect from the internet after the page loads. No analytics, no tracking, no cookies.

Yes. The “Download analysis” button saves a plain-text report containing the subject, all the metrics, the detected triggers, and the recommendations – handy for attaching to an A/B test summary or campaign brief.

Yes – free, unlimited, no signup, no watermark. Use the output in any context. Attribution to is appreciated but not required.