Free Tool
Email Subject Line Tester
A subject line is scored before sending, not after the open rate disappoints. This tester scores it on length, spam words, caps and truncation — and scans a whole email for spam-trigger words in the second mode.
Runs entirely in your browser. Nothing you type leaves your device, and nothing is stored or sent anywhere. The output is a planning aid built from the figures you enter — check the results before relying on them.
What this tool does
Paste a subject line and the tester scores it out of one hundred: length in the readable band, spam-trigger words from a local list, all-caps words, exclamation marks, questions and personalisation. It also shows where the line truncates in the main inboxes, because a perfect line that is cut off at the word that matters is not a perfect line.
The spam-word mode scans a full subject and body against the same local list and names the words it finds, with the count. The headline mode scores a headline on the same rules with a different length band. One word list, three entry points: the subject tester and the spam-word checker are one tool with two doors, because they share the same list and the same logic.
Sharing the list matters: if the subject mode and the body-scan mode used different lists, a word could pass one check and fail the other. One list means one answer.
Try it
Waiting. Paste a subject line — or switch to the spam-word scan or the headline mode — then press Calculate.
How it works
The subject score starts at 50. Length in the 30–50 band adds 20; a short line adds 5 and a long line loses 10. Each spam-trigger word costs 10, each all-caps word costs 5, each exclamation mark past the first costs 5. A question adds 5 and personalisation or a direct “you” adds 5. The score is clamped between 0 and 100.
The spam-word list is local — about two dozen phrases that filters commonly flag — and it is the same list for the subject mode, the body scan and the headline mode, so a word cannot pass one check and fail another. The list is a heuristic, not a filter: a clean scan does not guarantee delivery, because filters also weigh sender reputation, links and formatting.
Assumptions and limitations
A score is a heuristic. It is not an open-rate prediction.
- Truncation figures are pixel-width approximations — Gmail around 70 characters on desktop and fewer on mobile, Apple Mail around 46–65 — not exact counts. The front of the line matters more than the end.
- The spam list is the site’s own list of commonly flagged phrases. It is not a spam filter, and passing it does not guarantee delivery.
- The score is rule-based, not learned from data. A line can score 90 and still fail if the audience does not care, and a line can score 60 and win if it does.
- Personalisation is detected by a “you” or a merge field (a name in brackets). Real personalisation — a name, a past purchase — is stronger than either, and this tool cannot check for it.
Worked example
Example (illustrative inputs, not a real campaign). A plain subject line with no trigger words:
| Item | Figure |
|---|---|
| Subject | Your first 3 clients are closer than you think |
| Length | 47 characters — in the 30–50 band |
| Spam-trigger words | None |
| Score | 90 / 100 |
| Spam scan on the example body | 8 trigger words found |
Frequently asked questions
What does the score actually measure?
How closely the line follows a set of rules: length, spam-trigger words, caps, exclamation marks, questions and personalisation. It is a heuristic score, not an open-rate prediction — a high score means the line follows the rules.
Why is my subject line truncated in the inbox?
Because inboxes cut long lines: Gmail around 70 characters on desktop and fewer on mobile, Apple Mail around 46–65. The words that matter must come first — the end of a long line is never seen.
Does a clean spam scan guarantee delivery?
No. Filters weigh sender reputation, authentication, links, images and formatting alongside words. A clean word list removes one risk; it does not remove the others.
Why do the subject tester and the spam checker share a page?
Because they share the same word list and the same logic. Two pages with two lists would disagree about the same word — one list, three entry points, one answer.