Free email tool

Write a subject line worth opening.

Get a clear score, see what's helping or hurting, and make the next version stronger in under a minute.

0 characters
Paste one subject line. We'll check the words, structure, length, and inbox fit.
Try an example:
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Your score will appear here
You'll also get a five-part breakdown.

What to improve

Start with the changes that make the biggest difference.

Want 10 stronger versions?

We'll rewrite your subject line from ten useful angles, so you can pick the one that fits your email.

  • Direct, curiosity, benefit, and question angles
  • Made from the subject line you just tested
  • Free. Unsubscribe any time.

Your 10 improved versions

Use these as starting points. Keep the promise honest and aligned with the email.

What the score checks

Inbox fit

Useful length, careful emoji use, and fewer risky promotional signals.

Reader pull

A clear reason to care, with enough specificity or curiosity to earn attention.

Human touch

Natural phrasing, direct language, and relevant personalization cues.

How to write a subject line that gets opened

A subject line has one job: earn the next second of attention. It does that by giving the reader a specific reason to care, in language that sounds like a person wrote it. The patterns below are what this tool checks for, and they hold across newsletters, product emails and cold outreach alike.

Lead with the useful idea

Most inboxes cut subject lines after roughly 40 to 60 characters, so the important words belong at the front. "The welcome email mistake I made for 6 months" puts the lesson first; "Hi there, quick update about a mistake I made" buries it. Aim for 28 to 55 characters total - long enough to say something concrete, short enough to survive the cut.

Be specific, not loud

Specificity is what makes a subject believable. A number, a timeframe, a named outcome or a concrete constraint ("the 3-part checklist", "what changed after 90 days") gives the reader something to evaluate. Loudness does the opposite: words like free, guaranteed, act now and limited time, plus all caps and stacked exclamation points, read as sales pressure and can hurt inbox placement too. Say what the reader gets, in plain language.

Sound like a person

Sentence case, natural phrasing, and the occasional "you" or "your" make a subject feel written rather than blasted. Curiosity helps when it is honest - a real question or a genuine lesson, not a fake cliffhanger. One relevant emoji can help a subject stand out; two or more compete with the message. When your draft has no obvious weakness, the next step is a clean A/B test against one meaningfully different angle, not a tiny word change.

Frequently asked questions

How long should an email subject line be?

Aim for roughly 28 to 55 characters. Most inboxes cut subjects off after about 40 to 60 characters, so put the important idea first and let the rest support it.

What makes a subject line get opened?

A clear, specific reason to care: a concrete benefit, a useful question, a mistake to avoid, or a specific lesson. Natural sentence-case phrasing that sounds like a person, not a promotion, consistently outperforms hype.

Which words hurt deliverability or opens?

Heavy promotional phrases like free, guaranteed, act now and limited time, combined with all caps and repeated exclamation points, read as sales pressure and can weaken both inbox placement and trust.

Should I use emojis in subject lines?

One relevant emoji can help a subject stand out; two or more usually compete with the message. Keep the strongest one or remove them.

Is this subject line tester free and private?

Yes. The tool is free, requires no signup to score a subject line, and all scoring runs in your browser - your subject line is not stored on any server.

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