An email subject line tester analyzes your subject line for length, spam trigger words, capitalization issues, and readability — then gives you an actionable score so you can optimize for higher open rates before you hit send.
Subject Line Details
Enter a subject line
Mobile Preview
iPhone Mail app (iOS)
Desktop Preview
Gmail inbox (desktop)
How to Use the Email Subject Line Tester
Your email subject line is the single most important factor in whether subscribers open your email or ignore it. Studies consistently show that 47% of recipients decide to open an email based on the subject line alone. This free email subject line tester helps you optimize every subject before you send.
Step 1: Enter Your Subject Line
Type or paste your email subject line into the input field. The tool analyzes it in real time — no need to click a button. You'll instantly see your character count, word count, emoji count, spam word detection, and an overall score out of 100.
Step 2: Add Sender Name and Preview Text
Fill in the sender name (what subscribers see as "From") and your preview text (the preheader that appears after the subject line in the inbox). These optional fields power the realistic mobile and desktop email previews so you can see exactly what your email looks like in the inbox before sending.
Step 3: Check Your Score and Suggestions
The score gauge shows your subject line's overall quality from 0 to 100. A score above 70 is good; above 85 is excellent. Below the gauge you'll find specific suggestions explaining exactly what to fix. Common issues include:
- Too long — subject lines over 60 characters are truncated on mobile
- Spam trigger words — words like FREE, URGENT, or ACT NOW flag spam filters
- Too many emojis — more than two emojis can look unprofessional
- ALL CAPS words — shouting at subscribers hurts open rates
- Excessive punctuation — multiple exclamation marks trigger spam filters
Step 4: Review the Mobile and Desktop Previews
The iPhone-style mobile preview shows how your subject line appears in the iOS Mail app, including truncation at around 37 characters. The Gmail desktop preview shows how the subject and preview text appear side-by-side in a typical inbox row. If your subject gets cut off on mobile, shorten it or move the most important words to the front.
Best Practices for Higher Open Rates
A great email subject line is specific, creates curiosity or urgency without being manipulative, and tells recipients exactly what's inside. Keep it between 30 and 50 characters, use 6 to 10 words, and lead with the most compelling part. Avoid vague phrases like "Check this out" — instead, be concrete: "Your August invoice is ready to download." Test multiple subject lines using A/B testing in your email platform and use this tool to pre-screen each variation before running the test.
FAQ
Is this email subject line tester free?
Yes, the Email Subject Line Tester is completely free with no limits. You can test as many subject lines as you like with no account, no signup, and no hidden fees. Everything runs locally in your browser.
Is my data safe and private?
Absolutely. Your subject lines are never sent to any server. All analysis happens entirely in your browser using client-side JavaScript. Nothing is stored, logged, or shared. Close the tab and everything is gone.
What is a good email subject line length?
The ideal length is between 30 and 50 characters. Shorter subjects (under 30 characters) can feel vague, while longer ones (over 60 characters) get cut off on most email clients and smartphones. Aim for 6–10 words that are specific and action-oriented.
What are spam trigger words in email subject lines?
Spam trigger words are phrases that email spam filters flag as suspicious — things like 'FREE!!!', 'ACT NOW', 'CLICK HERE', 'URGENT', and 'Make money fast'. Using these words can send your email straight to the spam folder before it even reaches the inbox.
Does using emojis in subject lines help or hurt open rates?
One or two relevant emojis can boost open rates by up to 56% according to various industry studies. However, using too many emojis or using them in B2B contexts can hurt deliverability and feel unprofessional. This tool flags when emoji usage may be excessive.
How is the subject line score calculated?
The score (0–100) combines several factors: character length (ideal 30–50 chars), word count (ideal 6–10 words), spam word penalties, ALL CAPS detection, emoji count, and punctuation patterns. A score above 70 is good; above 85 is excellent for most campaigns.
How many characters show on mobile before truncation?
Most mobile email clients display 30–40 characters of a subject line in portrait mode. The mobile preview in this tool shows a realistic iPhone-style cut-off so you can see exactly what subscribers see when your email arrives in their inbox.
What is preview text and why does it matter?
Preview text (also called preheader text) is the short snippet that appears below the subject line in the inbox list view. It acts as a second subject line and can significantly increase open rates. This tool lets you preview how your subject line and preview text look together in desktop and mobile views.