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An email subject line scorer evaluates a subject line against 14 criteria that influence inbox placement and open rates — character count, word count, Flesch Reading Ease, sentiment, spam trigger words, ALL CAPS usage, punctuation patterns and personalisation tokens. Each criterion scores out of 10, giving a maximum of 140 points, which the tool converts to a 0–100 percentage.
Run a free email subject line score at spotzee.com/tools/email-subject-score.

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Why this matters

Spam filters scan subject lines for many of the same signals this scorer checks. Spam words, ALL CAPS, excessive punctuation and fake reply prefixes like “RE:” all increase the probability of junk classification. A subject line that triggers these filters never reaches the inbox, regardless of how relevant the email content is. Subject line length matters too. Most mobile email clients display 30–50 characters before truncating. A subject line that reads cleanly on desktop may cut off at the critical word on a phone screen, breaking the hook that drives an open. And sentiment matters — negative-framed subject lines consistently underperform neutral or positive alternatives across most marketing audiences.

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Scoring criteria

The scorer evaluates 14 signals and awards up to 10 points for each:
CriterionWhat it measures
Character countTotal characters — penalises lines over ~50 chars
Word countTotal words — penalises very short or very long lines
Flesch Reading EaseHow easy the line is to scan at a glance
Flesch-Kincaid gradeReading grade level — lower is more accessible
SentimentPositive or negative emotional valence
Spam wordsCount of known spam trigger words
ALL CAPS wordsCount of fully capitalised words
Exclamation marksCount of ! characters
PunctuationOverall punctuation density
”RE:” prefixFake reply thread indicator
”FWD:” prefixFake forward indicator
”Free” mentionsCount of the word “free”
[FNAME] tokenPresence of personalisation merge tag
EmojisCount of emoji characters
A score of 70% or above clears the main spam signals and reads well. Between 50–69% there is at least one signal worth fixing. Below 50%, multiple issues are likely to reduce deliverability or open rates.

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How it works

1

Enter a subject line

Type or paste the exact subject line you plan to send, including any personalisation tokens such as [FNAME] or emojis.
2

Analyse 14 criteria

The scorer evaluates each of the 14 signals listed above and assigns a score out of 10 for each.
3

Calculate the score

Total earned points are divided by 140 and expressed as a percentage.
4

Read the breakdown

The result highlights the specific criteria that reduced the score so you know exactly what to fix.

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What to watch for

  • Spam words detected. Remove or replace any flagged spam trigger words. Common offenders: “act now”, “click here”, “guaranteed”, “100% free” and urgency phrases. Even one can reduce inbox placement.
  • ALL CAPS words. Rewrite in sentence or title case. ALL CAPS words feel aggressive and trigger spam filters.
  • Negative sentiment. Neutral or positive framing performs better for marketing email. If your subject line tests negative, reframe the value without changing the offer.
  • Subject is too long. Aim for under 50 characters — ideally 30–40 — for mobile. Long subjects truncate at the critical word.
  • RE: or FWD: prefix. Remove these. Faking thread history in marketing email is a spam signal that spam filters and recipients both recognise.
  • “Free” appears in the subject. Consider alternatives: “complimentary”, “no cost”, or framing what is included rather than the price.

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FAQs

The subject line tester scores 14 criteria: character count, word count, Flesch Reading Ease, Flesch-Kincaid grade level, sentiment, spam trigger words, ALL CAPS word count, exclamation marks, punctuation count, “RE:” prefix, “FWD:” prefix, “free” mentions, [FNAME] personalisation tokens and emoji count. Each is worth up to 10 points, giving a maximum of 140, which converts to a 0–100 percentage.
70% or above indicates a subject line that clears the main spam signals and reads well. Between 50–69% suggests at least one signal worth fixing before sending. Below 50% means multiple issues are likely hurting deliverability or open rates — revise before scheduling.
“Free” is one of the most abused words in spam email and is heavily weighted by spam filters. A single use does not guarantee filtering, but it raises the probability — especially when combined with other spam signals in the same subject line.
Flesch Reading Ease scores text on a 0–100 scale based on average syllables per word and words per sentence. For subject lines, higher scores (60+) mean the subject is easy to scan at a glance, which correlates with faster open decisions. The tool uses this score to assess scannability.
Yes — the scorer rewards subject lines that include a [FNAME] personalisation token. If your email service provider uses a different merge tag format (e.g. {{first_name}}), the checker may not recognise it. Use the standard [FNAME] token when testing to get an accurate score.
After scoring, use the email subject line suggester to generate alternative subject lines tuned to your content. Run the scorer on each suggestion to compare scores before choosing which to send.

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Try it

Score any subject line at spotzee.com/tools/email-subject-score. No sign-up needed for the one-shot web check. Programmatic access deducts a small per-call amount from your Spotzee credit balance — see live per-tool pricing on the Spotzee pricing page.