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Email Subject Line Tester

The subject line decides whether your outreach or newsletter gets opened. This tester checks the four factors you control: character length (20–55 keeps it whole on mobile), word count, spam-trigger words that hurt deliverability, and shouting signals like ALL-CAPS and stacked exclamation marks.

Length
0 chars

Aim for 20–55 characters (mobile-safe)

Word count
0

3–9 words performs best

Spam-trigger words
0

None found ✓

ALL-CAPS runs
No ✓

All-caps hurts deliverability

Exclamation marks
0

OK

It runs entirely in your browser and updates as you type, so you can iterate until every check is green. Pair it with the outreach email generator for a complete pitch.

How to Use the Email Subject Line Tester

  1. 1Type or paste your subject line.
  2. 2Check the length indicator — 20–55 characters is mobile-safe.
  3. 3Remove any flagged spam-trigger words.
  4. 4Iterate until checks are green, then send.

Frequently Asked Questions

What is the best subject line length?
20–55 characters (3–9 words). Mobile clients truncate around 30–40 characters, so put the hook in the first three words.
Which words trigger spam filters?
Classic offenders include 'free!!', 'act now', 'guarantee', 'earn money', '$$$', and 'limited time'. One is rarely fatal; several together, plus all-caps, will hurt inbox placement.
Do emojis help or hurt subject lines?
In B2C newsletters a single relevant emoji can lift opens slightly; in cold outreach to editors it usually reads as spam. When in doubt for pitches, skip it.

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