Score length, spam words, emoji & urgency — see your inbox-vs-spam risk
Heuristic scorer, not a real spam filter. This tool estimates how inbox-friendly a subject line reads. It does not connect to Gmail, Outlook or Apple Mail. Real deliverability depends mostly on sender reputation, authentication (SPF/DKIM/DMARC), list hygiene, engagement history and the full message body — none of which a subject-only tool can see. Everything is analyzed in your browser; your subject line is never uploaded or stored.
Type a subject line and the tool parses five signals from that single string — length, spam-trigger words (tiered High/Medium/Low), punctuation & ALL-CAPS, emoji, and urgency — then blends them into a single composite inbox score (0–100) with a verdict band. Spam words and punctuation carry the most weight because they are the strongest inbox-vs-spam signals; length and urgency are open-rate (engagement) signals. You also get an inbox preview showing where mobile/desktop truncate, a prioritized "top 3 fixes" list, and an optional directional open-rate estimate.
Take the line "FREE gift!! Act now — limited time offer" (40 characters, 8 words, device "Both"):
The top fix is the spam-word stack: dropping "free" and "act now" and toning down "!!" lifts the line into the green band without losing the message.
composite = round(
0.25 × length_score
+ 0.32 × spam_score
+ 0.20 × punctuation_score
+ 0.10 × emoji_score
+ 0.13 × urgency_score )Each sub-score is 0–100 (higher = better). Characters and emoji are counted with grapheme segmentation so a multi-codepoint emoji (skin tones, family emoji) counts as 1, not 4–7. Spam words match on word boundaries, so "free" never fires inside "freedom" and "sale" never fires inside "wholesale".
| Composite | Verdict |
|---|---|
| 85–100 | Likely inbox · Strong open potential |
| 70–84 | Likely inbox · Good |
| 55–69 | Inbox at risk · Needs work |
| 40–54 | Spam risk · Revise |
| below 40 | High spam risk · Rewrite |
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style="width:100%;max-width:560px;height:820px;border:0;"
title="Email Subject Line Tester" loading="lazy"></iframe>
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Most evidence clusters the sweet spot at about 20–50 characters or 6–10 words. Mobile inboxes truncate around 33–50 characters and desktop around 70, so front-load the value: aim for roughly 28–40 characters if most of your opens are on mobile, 40–60 on desktop.
No. This is a writing-quality heuristic, not a connection to Gmail, Outlook or Apple Mail. Real deliverability depends mostly on sender reputation, authentication (SPF/DKIM/DMARC), list hygiene, engagement history and the full message body — none of which a subject-only tool can see. Treat the score as guidance for writing a stronger line.
On their own, rarely. Modern filters score the whole message and weigh sender reputation far above subject keywords. A single word like "free" in an otherwise clean, well-sent email is minor — it becomes a problem when it stacks with ALL-CAPS, exclamation overuse and other triggers. That is why the tool tiers and weights words rather than failing on any single match.
The research is genuinely mixed. Some studies show a lift (MailerLite found top campaigns were 21% more likely to use an emoji); others show harm (Nielsen Norman found emoji raised negative sentiment ~26% and seasonal emoji drew 2–4× the complaints). The tool flags emoji rather than scoring it harshly: 1–2 are generally safe, and it is audience- and occasion-dependent.
It is directional only, not a prediction. It anchors to a generic ~21% baseline and scales with your composite score, then shows a ±5-point range. Reported open rates are also inflated by Apple Mail Privacy Protection, which auto-loads images and registers phantom opens for roughly 46% of the market. Compare to your own industry and list benchmarks.
Light, honest urgency ("Ends today") can raise opens, so the tool rewards a single balanced urgency marker. It only penalizes manufactured, stacked urgency (three or more markers like "ACT NOW — last chance, expires today, final hours"), which reads as pressure and trips spam heuristics.
No. The entire analysis runs in your browser. Your subject line, preheader and sender name are never sent to a server, uploaded or stored. The tool works offline once the page has loaded.
🔒 Everything is calculated in your browser. We don't store or sell your data.