What is the ideal email subject line length?

The optimal length is 41-50 characters (6-10 words). This ensures the full subject line is visible on both desktop and mobile email clients.

What are spam trigger words?

Spam trigger words are terms like 'free', 'act now', 'limited time', 'click here', or '$$$' that spam filters flag. Using too many can send your email to the spam folder.

Does this tool send my data anywhere?

No. All analysis runs entirely in your browser. Your subject lines are never sent to any server.

📧 Email Subject Line Tester

Score your email subject line, detect spam words, preview inbox appearance, and A/B compare variants.

Enter your email subject line

How the Subject Line Tester Works

Enter your email subject line and get an instant score out of 100 based on length, word count, spam triggers, personalization, and best practices. All analysis runs in your browser.

Scoring Criteria

Character count — Optimal range is 41-50 characters
Word count — 6-10 words is the sweet spot for open rates
Spam trigger words — Penalized for words that trigger spam filters
Personalization — Using tokens like [name] boosts engagement
Emoji usage — A single emoji can increase open rates by 56%
Numbers — Subject lines with numbers tend to perform better
ALL CAPS — Penalized as it triggers spam filters and reduces trust
Excessive punctuation — Multiple !!! or ??? are flagged

A/B Comparison

Enter two subject line variants to see scores side by side. The tool highlights which one is stronger and why.

📧 Email Subject Line Tester

📋 Analysis Checks

⚠️ Spam Trigger Words Found

📱 Inbox Preview

💡 Improvement Suggestions

Subject A

Subject B

How the Subject Line Tester Works

Scoring Criteria

A/B Comparison