Free Cold Email Subject Line Tester & Open Rate Optimizer
Score cold email subject lines for open rate probability. Analyzes character length, mobile truncation, sentiment, personalization tags, and spam words.
Open Rate Potential
🟡 Good (35-50% Open Rate)
Metrics
5 Words • 45 Characters
Impact Score
Truncated on Mobile
Cold Outreach Deliverability Audit
Why Cold Outbound Teams Use Our Free Subject Line Tester
0-100 Open Rate Impact Score
Mobile character cutoff alert
Personalization tag validator ({{firstName}})
Email Deliverability Standards (US & UK Outbound Guidelines)
In February 2024, Google Workspace and Yahoo introduced strict anti-spam enforcement rules that mandate proper SPF, DKIM, and DMARC authentication for all outbound mailboxes. If your DNS records have syntax errors or exceed the 10-lookup threshold, incoming mail servers will silently route your cold outreach into the Spam folder or reject connections entirely.
Requires valid physical postal address in signatures, accurate From header identification, and clear opt-out mechanics.
Permits B2B outreach under legitimate interest when targeted to relevant corporate decision-makers with authenticated sender identity.
Frequently Asked Questions About Subject Line Tester
What is the ideal word count for cold email subject lines?
Between 2 to 5 words (under 40 characters). Casual, lower-case, internal-sounding subject lines (e.g., "quick question", "intro: alex <> sarah") achieve the highest open rates.
Should I use title case or lower case in cold email subject lines?
Lower case or sentence case consistently outperforms Title Case. Marketing-style Title Case signals an automated blast, whereas lower case mimics an authentic email from a peer.
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