MetSender
Free Subject Line Checker Tool
Test and optimize your email subject lines for maximum open rates and deliverability. Analyze length, spam score, mobile preview, and get actionable insights to boost your email performance.
Characters: 0 | Words: 0
What is a Subject Line Checker?
A subject line checker is an essential email marketing tool that analyzes your email subject lines to predict open rates, identify spam triggers, and ensure optimal formatting across devices. Our free subject line checker helps marketers create compelling subject lines that reach the inbox and drive engagement.
Key Features of Our Subject Line Checker
Length Optimization
Analyze subject line length for optimal display across email clients and mobile devices.
Spam Score Analysis
Detect spam triggers and promotional language that could hurt your deliverability.
Mobile Preview
See how your subject line appears on mobile devices where most emails are opened.
Open Rate Prediction
Get insights on potential open rates based on subject line best practices and patterns.
Character Analysis
Monitor character count, word count, and special character usage for optimization.
A/B Testing Ready
Compare multiple subject line variations to find the most effective option.
How to Use the Subject Line Checker
Enter Subject Line
Type your email subject line in the input field above.
Analyze Instantly
Get real-time analysis as you type or click analyze for detailed results.
Review Insights
Get detailed feedback on length, spam score, and mobile optimization.
Optimize & Test
Apply suggestions and test variations to maximize open rates.
Subject Line Best Practices
Length Guidelines
- • Keep subject lines under 50 characters for mobile
- • Aim for 6-10 words for optimal readability
- • Front-load important keywords
- • Avoid excessive punctuation
- • Test different lengths for your audience
- • Consider preview text integration
Content Strategy
- • Create urgency without being spammy
- • Use personalization when relevant
- • Ask questions to spark curiosity
- • Include numbers and specific benefits
- • Avoid all caps and excessive symbols
- • Match subject line to email content
High-Converting Subject Line Examples
✓ Good Examples
- "5 minutes to boost your sales by 30%"
- "Your invoice is ready, [Name]"
- "Last chance: 50% off ends tonight"
- "Quick question about your project"
- "Free guide: Double your email opens"
✗ Avoid These
- "URGENT!!! LIMITED TIME OFFER!!!"
- "Make money fast with this secret trick"
- "FREE FREE FREE - Click here now!"
- "Congratulations! You've won $1000"
- "RE: Important business proposal"
Frequently Asked Questions
What's the ideal subject line length?
The optimal length is 30-50 characters or 6-10 words. This ensures full visibility on mobile devices where 80% of emails are opened.
How does the spam score work?
Our spam score analyzes trigger words, excessive punctuation, all caps usage, and promotional language patterns to predict deliverability issues.
Can I test multiple subject lines?
Yes! Test different variations to compare performance metrics and find the most effective subject line for your campaign.
Does this tool store my subject lines?
No, we do not store or save any subject lines you test. All analysis is performed in real-time without data retention.
How accurate are the open rate predictions?
Our predictions are based on industry benchmarks and best practices. Actual results may vary based on your audience, sender reputation, and content.