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Email Subject Line Tester
Paste your subject line and get an instant score across 6 dimensions — length, spam signals, readability, specificity, mobile preview, and hook strength.
Type a subject line above to see your score
Subject lines worth stealing
Real examples for service businesses — organized by email type.
Following up on your bathroom remodel estimate — #1042
ContractorYour plumbing quote — any questions before we start?
PlumberHVAC estimate ready — valid through Friday
HVAC TechnicianRe: Landscaping proposal — still interested?
LandscaperYour home listing proposal — ready to review
Real Estate AgentRoof repair estimate — quick question before I finalize
ContractorPhotography package quote — 3 options for your event
PhotographerDid you get a chance to look at the legal estimate?
LawyerElectrical quote #2847 — following up
ElectricianInterior design proposal — following up on your feedback
Interior DesignerWhat makes a subject line work
Be specific, not clever
"Invoice #2847 from Johnson Plumbing" outperforms "Important update" every time. Recipients open emails when they know exactly what's inside.
Front-load the key info
Mobile clients cut off at ~50 characters. Put the most important words first — don't bury the point at the end.
Use numbers when you can
Numbers add credibility and specificity: "3 things to review before we start" or "Quote #1042 ready" are more clickable than vague alternatives.
Test variations
If you send to a large list, A/B test two subject lines. Even a small improvement in open rate compounds into significantly more responses over time.
Frequently Asked Questions
The best subject lines are specific (say exactly what the email is about), short (30–50 characters), and free of spam words. For service businesses, subject lines that include a specific reference — like an invoice number, job type, or client name — consistently outperform generic ones.
30–50 characters is the sweet spot. Most mobile email apps cut off subject lines around 50 characters, so anything longer gets truncated. Desktop clients show a bit more, but the first 50 characters determine whether someone opens the email.
Spam filter trigger words include: FREE, GUARANTEED, ACT NOW, LIMITED TIME, BUY NOW, CLICK HERE, and CONGRATULATIONS. Also avoid all-caps words, multiple exclamation marks, and dollar signs — they signal spam to both filters and real humans.
Yes — subject lines that end with a question tend to get higher open rates because they create an information gap the reader wants to close. Works best for follow-up emails ("Still interested in the quote?") and check-ins ("Did you get a chance to review the proposal?").
The score is based on 6 dimensions: length (optimal 30–50 chars), spam signals (trigger words, caps, punctuation), readability (capitalization, structure), specificity (numbers, action nouns, personalization), mobile preview (truncation risk), and hook strength (question, number, direct address). Each dimension is weighted and combined into a score out of 100.
For service businesses, the most effective follow-up subject lines are specific and low-pressure: "Following up on your estimate — #1042", "Quick question about the kitchen remodel quote", or "Your proposal from [Company] — still interested?". Avoid vague ones like "Following up" or "Checking in".
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