SaaS Email Subject Line Tester & Spam Checker
Test email subject lines for character count, mobile truncation, urgency triggers, and common spam trigger words. Free interactive tool.
Character Count
54 chars
Optimal (30-50 chars)
Deliverability Score
100/100
High Deliverability
Spam Trigger Words
0
None detected
About this tool
The subject line is the single most critical factor determining whether your retention, billing, or win-back emails are opened or consigned to the spam folder. Because a large share of email is read on phones, subject lines exceeding 50 characters are automatically truncated by mobile email clients (like Apple Mail and Gmail for iOS), cutting off your most important value proposition. Furthermore, including aggressive marketing buzzwords ('Free', '100% guarantee', 'Winner', 'Act now!') triggers automated mailbox spam filters, severely degrading domain sender reputation across your entire transactional infrastructure. Use this interactive subject line tester to inspect character counts, preview mobile readability, and scan for spam trigger words before hitting send.
How It Works
- 1Type or paste your candidate email subject line.
- 2Inspect real-time character count and word count.
- 3Review the mobile length status (optimal between 30 and 50 characters).
- 4Check detected spam trigger words and urgency flags to evaluate your overall deliverability score.
Worked Practical Example
Test candidate subject line: 'Claim your free trial winner before it expires!'
Calculation / Steps
Length = 49 chars (Optimal). Spam words detected: 'free', 'winner'. Deliverability Score: 70/100.
Expected Result
Remove spam trigger words to maximize inbox placement across Gmail and Outlook.
Frequently Asked Questions
What is the ideal character length for an email subject line?+
Between 30 and 50 characters (approx 6 to 9 words). This ensures the full subject line renders cleanly on mobile phone screens.
Do emojis in subject lines hurt B2B open rates?+
In professional B2B software, emojis can trigger spam filters and often look unprofessional to corporate IT buyers. Test sparingly.
Why are transactional subject lines so important?+
Billing failure and renewal notices require urgent, unambiguous phrasing (e.g. 'Action required: Update payment method') to prompt immediate action.
Automate retention on your cancel button
BoolBul helps you avoid relying exclusively on email open rates by catching cancelling users directly in-app while their session is active.
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