Email Subject Line Tester
Test subject lines for character length, spam triggers, and mobile preview truncation.
No spam triggers detected.
No personalization tags. Add {{name}} or [name] for better open rates.
About this tool
Subject lines determine open rates — too long gets truncated on mobile, spam trigger words hurt deliverability.
Test length, spam warnings, and mobile preview locally before sending campaigns.
How to use the Email Subject Line Tester
- 1
Type or paste your email subject line.
- 2
Review character count, spam word warnings, and mobile preview.
- 3
Iterate until length and wording are optimized for inbox display.
Subject line craft
Front-load the value proposition — mobile shows roughly 40 characters. Avoid ALL CAPS and excessive punctuation.
Personalization tokens add length — account for them when checking character count.
Pro tips
- A/B test two subject lines on 10% of list before full send.
- Avoid spam triggers like "free", "act now", and "guarantee" unless essential.
Social Media Specs & Character Limits
Optimal text formatting, length guidelines, and parameters for all major platforms:
| Platform | Max Length | Ideal Length | Hashtag Policy |
|---|---|---|---|
| Instagram Feed & Reels | 2,200 chars | 125 - 150 chars | 3 - 5 tags (Recomm.) |
| TikTok Posts | 4,000 chars | 100 - 200 chars | 3 - 5 tags (Ideal) |
| YouTube Description | 5,000 chars | 1,500 chars (SEO) | 3 - 10 tags |
| X / Twitter Post | 280 chars | 100 - 140 chars | 1 - 2 tags |
| LinkedIn Articles & Posts | 3,000 chars | 500 - 1,000 chars | 3 - 5 tags |
Related tools
All tools →Headline Formula Generator
Generate headlines from proven copy formulas
Slogan Generator
Create taglines from templates — no AI required
Acronym Generator
Build acronyms and backronyms from phrases
ASCII Art Generator
Convert text into simple ASCII art banners
Aspect Ratio Calculator
Calculate image ratios and social media dimensions
Banned Hashtag Checker
Check hashtags against a static banned list
Frequently Asked Questions
Does this send test emails?▼
No. This is a local preview and analysis tool — no emails are sent and nothing is uploaded.
What subject line length works best?▼
Aim for 40–60 characters for mobile visibility. Front-load the most important words.