Inputs
01Up to 12 subject variants
Paste multiple subject lines (and optional preheader/preview text). Scoring is browser-side and deterministic for the ruleset no ESP open-rate API is queried. Near-duplicates are flagged so tests stay informative.
Scoring model
02How open potential is calculated
- Base score starts mid-band; good findings add less than bad findings subtract (strict calibration).
- Excellent is rare (≥90). Good / fair / needs-work bands are intentionally strict.
- Variants are ranked live; near-duplicates are flagged so A/B tests stay meaningful.
- Optional preview text is scored for pairing (truncation + support of the subject promise).
Pillars
03What gets scored
- Length / mobile truncation risk
- Framework detection (how-to, question, reply-style, etc.)
- Power words and curiosity structure
- Spam lexicon dual score (content risk vs open potential)
- Formatting noise (caps, punctuation, emoji density)
- Preheader pairing when provided
Worked interpretation
04Picking a test set
Example: twelve variants rank with a clear top three. The leader is specific and mobile-safe but shares a spammy token with a lower-ranked line. A curiosity framework line scores mid-band because length truncates on mobile. Near-duplicates of the leader are flagged.
- Ship 2–3 structurally different winners, not ten rephrases of one line.
- If spam dual score is elevated, prefer the cleaner runner-up for cold lists.
- Use preheader to complete the promise rather than repeat the subject verbatim.
Limits
05What this does not mean
- Not a forecast of your list’s open rate (list quality, sender, timing dominate).
- Not a guarantee any ESP filter will treat the line the same way.
- Does not score body HTML (use the Spam Score Checker for body risk).