Email Subject Line Tester & Spam Checker
Test and score email subject lines for open rates, mobile character truncation, spam trigger words, and inbox deliverability across Gmail and Outlook.
Grade: A+ (High Open Rate)
Compose Subject & Preheader
Mobile Inbox Preview (Gmail / iOS)
This simulator accurately previews how your subject line and preheader appear on an iPhone or Android notification and Gmail inbox list view.
Optimizing Email Deliverability and Open Rates
Over 47% of email recipients decide whether to open an email based solely on the subject line, while 69% report emails as spam based on the subject line alone. With over 60% of emails opened on mobile devices where subject lines are truncated after 30 to 45 characters, testing your subject lines against spam triggers, length restrictions, and emotional sentiment is essential to safeguard domain reputation and avoid the spam folder.
Key Performance Features
Mobile Truncation Previews
Visual mobile inbox preview simulating Gmail, Apple Mail, and Outlook cutoff thresholds (35 to 50 characters).
Spam Word Filter Detection
Scans across 100+ proven spam triggers (e.g. '100% Free', 'Act Now', 'Risk-Free', 'Cash Bonus', excessive caps).
Engagement & Sentiment Grader
Scores emotional curiosity, urgency, numbers/data presence, and personalization token utilization.
Preview Text (Preheader) Pairing
Test how your subject line pairs with the email preview text for maximum click-through appeal.
A/B Subject Line Variants
Provides instant AI-style recommendations and alternative angles for multivariate split-testing.
Overall Deliverability Score
Comprehensive 0 to 100 deliverability index rating your probability of landing in the primary inbox.
Creator & Agency Applications
- ✓E-Commerce Promotional Blasts
Maximize Black Friday, Cyber Monday, and flash sale revenue without triggering ISP promotional tab filtration.
- ✓B2B Cold Email Outreach
Keep cold outreach emails landing in corporate Outlook and Google Workspace inboxes.
- ✓Substack & Newsletter Publishers
Craft irresistible editorial hooks that drive industry-leading 45%+ newsletter open rates.
- ✓D2C Automated Welcome Sequences
Fine-tune customer onboarding and abandoned cart email open rates.
Frequently Asked Questions
What is the optimal character length for an email subject line?
The sweet spot is between 30 and 50 characters (or 4 to 7 words). Subject lines in this range display completely on mobile devices like iPhones and Androids without being cut off with an ellipsis (...).
What words trigger email spam filters?
Common spam triggers include aggressive sales hype ('100% Free', 'Urgent', 'Guaranteed', 'No Risk', 'Make Money Fast'), excessive exclamation points, and typing in ALL CAPS. Using these frequently causes Gmail and Outlook to route your emails to the Junk folder.
Do emojis in subject lines increase open rates?
Emojis can increase open rates by 10% to 15% in B2C e-commerce when used sparingly (1 emoji max). However, in professional B2B cold outreach, emojis can look spammy and may trigger corporate spam filters.
What is preheader text and why does it matter?
Preheader text (or preview text) is the short snippet of text that appears next to or below your subject line in the inbox. Pairing a punchy 35-character subject line with an engaging 80-character preheader essentially doubles your promotional real estate.
Related Marketing Calculators
Need a Brain Break? ☕
Done working on your task? Take a quick 60-second break, test your reflexes, and flap through infinite pixel obstacles in Sky Flap!