This free email subject line tester scores your subject line from 0 to 100 as you type, checking length, word count, spam-trigger words, ALL-CAPS, punctuation, emojis, personalization, and power words — then shows a live inbox preview of how it renders on mobile and desktop. No signup, fully private in your browser.
Try an example:
Truncation points are approximate — exact cut-offs vary by client and screen width.
Type a subject line to see your score.
IGSendMail's AI subject line generator drafts and A/B-tests high-scoring lines, then sends from a fully authenticated domain so they actually reach the inbox.
This subject line checker runs eight deterministic heuristics entirely in your browser and combines them into a single 0–100 score. Nothing is uploaded — the same input always produces the same result, so you can A/B your wording with confidence.
Rewards 28–50 characters; penalizes over 60 (mobile truncation) and under 15 (too vague).
Rewards a scannable 3–9 words and nudges down very short or wordy lines.
Scans against ~60 known spam phrases and flags each one it finds.
Penalizes ALL-CAPS words and excessive !!! or multiple ? marks.
Mild positive for one emoji; penalizes three or more.
Detects merge tags like {name}, {{first_name}}, %FNAME%, *|FNAME|*.
Rewards emotional and curiosity drivers from a 40+ word list.
Small boost for a digit and for a question that sparks curiosity.
The subject line is the single highest-leverage piece of copy in any email. It is the only thing — alongside the from name and preview text — that the recipient sees before deciding to open, archive, or report. A subject line that is too long gets cut off on mobile, where the majority of email is now read; one stuffed with spam-trigger words and ALL-CAPS can be filtered out before a human ever sees it. Even a few points of open-rate improvement compounds across every downstream metric: clicks, conversions, and revenue.
That said, no subject line can rescue a poor sending reputation. Mailbox providers weigh authentication, engagement history, and list hygiene far more heavily than wording. Use this tester to sharpen the words, and let IGSendMail's deliverability stack handle the reputation side so your well-crafted line actually lands in the inbox. For a full domain check, run our free deliverability audit.
Score your wording here, then send it through IGSendMail — automatic SPF/DKIM/DMARC, an AI subject line generator, and 99% inbox delivery, all on the free plan.