Subject Line Tester — Score Your Line Before You Send
Who this is for: For anyone about to hit send on one email that matters — and for marketers screening a week of campaigns in one sitting.
Paste a subject line — get a 0–100 score, client truncation previews, and the exact fixes that raise it.
Quick answer: A good subject line is 26–50 characters, names a concrete number, speaks to 'you', and opens a curiosity loop — 'Your Q4 plan: 2 spots left this month' scores 81/100 on those checks. Paste your line below for a 0–100 score with itemized fixes.
The ten checks
- Length 37 chars — the sweet spot (mobile shows ~35, desktop ~70).
- Word count 8 words — scannable at a glance.
- Concrete number A number — specifics read as credible and get opened.
- Curiosity frame Statement only — a question frame adds pull.
- Second person Speaks to the reader directly — the strongest single lever.
- Power words No emotional trigger words — one curiosity/urgency word helps.
- Emoji No emoji — fine for B2B; one can lift B2C opens.
- Capitalization Sentence case — reads like a person, not a promo.
- Exclamations No exclamation marks — calm reads confident.
- Spam words Clean against the 175-word trigger list.
Where clients cut it off (approximate)
Scoring runs entirely in your browser — nothing is uploaded. Scores grade the checklist, not your list; your own open data makes the final call.
| Scoring | 30 base + up to ~60 add-points − penalties, 0–100 |
|---|---|
| Sweet band | 26–50 chars · 4–8 words |
| Client cuts | 35 / 45 / 60 / 65 / 70 chars (Gmail app→Gmail web) |
| Biggest levers | Number +8 · you/your +8 · power word +7 |
| Worked example | "Your Q4 plan: 2 spots left this month" → 81 Strong |
| Status | Rules follow public email-marketing benchmark practice (2026): ~35–70 visible characters by client, 175-word spam trigger list, sentence case, one clear idea per line. Client truncation figures are engineering approximations — devices, fonts and zoom shift them. |
How does this subject line tester work?
The tester scores your line on ten weighted checks, all visible. Length (25 pts): the 26–50 character band shows in full on most clients — mobile shows roughly 35 characters, desktop Gmail about 70. Words (10): 4–8 words scan at a glance. Plus up to 33 more for a concrete number (8), a curiosity or question frame (6), second person 'you/your' (8), an emotional power word (7) and 1–2 emoji (4). Deductions hit ALL-CAPS shouting (−12 to −20), exclamation stacking (−8), and spam trigger words (−3 to −24). A worked example: 'Your Q4 plan: 2 spots left this month' scores 81 — 37 characters, 8 words, a number, second person. 'URGENT!!! 100% FREE miracle offer inside!!!' scores 26 — spam triggers and triple exclamation marks burn it down. Same product, opposite inbox fate.
Common uses
- Checking the one email that really matters before it goes out
- Screening a whole campaign calendar line by line
- Teaching new hires what a good subject line looks like, with reasons
- Comparing a draft against the score it replaces
What the score does not know
The tester reads the line, not your list. It can't see that your subscribers love ALL-CAPS Tuesdays, that your sender reputation is pristine, or that 'webinar' belongs in your world. Treat 40s as drafts to fix and 80s as drafts to ship — then let your own open data make the final call.
Frequently Asked Questions
What is a good subject line score?
How long should an email subject line be?
Do emojis in subject lines help?
Does the tester send my text anywhere?
Why did my line score lower than I expected?
More guides
11 cold email subject lines that earn the open — organized by play, with the scored engine results and what to steal from each.
Subject line plays for newsletters specifically — habit, naming conventions, issue numbering, and 12 scored examples.
The seven-step process for writing subject lines that get opened — draft, check, trim, preview — with the ten checks that matter in 2026.
More Writing & scoring tools
Pick a goal and industry — get 10 ready-to-send subject lines, each scored, with a reroll for fresh sets.
Paste your line — see which of the 46 power words it hits, by emotion category, with usage notes.