Content
Subject Line Tester
Paste a subject line. We score clarity, length, casing, punctuation, and spam-trigger phrases, then show how it renders across the inboxes that matter.
Want the bigger picture? Read Subject line best practices in the Email Almanac.
How it works
Five signals, weighted
The overall score blends five signals. Each one stands on its own in the breakdown so you can fix the right thing.
- Clarity and impact (30%). Generic openers and filler words drag this down. Numbers and specific nouns lift it. The biggest single lever.
- Content risk (20%). Two phrase lists, high risk and moderate. Hits never block you on their own, but they stack with reputation and authentication signals.
- Length (20%). The sweet spot is 25 to 55 characters. Anything over 70 gets clipped on iPhone first, then Android and Yahoo mobile.
- Capitalization (15%). All caps reads as shouting. One word in caps for emphasis is fine; multiple words start to feel aggressive.
- Punctuation and emoji (15%). Stacked exclamation marks, multiple dollar signs, and emoji clusters all add risk. One of each is rarely a problem.
When to use it
Three moments worth checking
The tool is built for fast, repeated use at the points where small subject changes move open rates the most.
- Before every send. 30 seconds of polish on the subject is the cheapest open rate lift in email.
- When opens drop. If a sequence stops performing, run the recent subjects through one by one. Patterns show up quickly.
- A/B test prep. Run both variants. If one scores significantly lower, think twice before shipping that arm against half your list.
Related reading
From the Email Almanac
Two short reads that pair with this tool.
Want more than a subject score?
Subject lines are one input. We read every signal that affects whether your mail lands in the inbox and write you a plain-English report.
Try it deeper with RME