Deliverability Checkers — Spam Words, Length & Inbox Preview

The inbox judges your email twice: once on vocabulary (spam filters) and once on geometry (truncation). These three tools check both before your subscribers do — the spam word scanner flags high-risk and medium-risk words with severity, the length analyzer renders each client's cut, and the inbox preview shows the subject-plus-preheader compound exactly as the inbox list stacks it.

The tools

Spam Word CheckerScan your subject line against 175 spam trigger words — high-risk and medium-risk flagged, with fixes.Subject Line Length AnalyzerSee exactly where Gmail, Outlook, Yahoo and Apple Mail cut your line — and the character band that fits.A/B Subject Line ComparerTwo lines side by side — scores, check-by-check differences, and the verdict on which to send.Inbox Preview ToolSubject + preheader rendered as Gmail desktop, Gmail mobile and Outlook will show them — before you send.

Words are the dress code, not the bouncer

In 2026, spam filtering leans on domain reputation, authentication (SPF/DKIM/DMARC) and reader engagement far more than word lists — but vocabulary still matters at the margin, especially for new senders and cold outreach. The checker splits 175 trigger words into 107 high-risk (never legitimate) and 68 medium-risk (fine alone, risky stacked), so you spend your edits where they count instead of scrubbing every 'sale' from your calendar.

The 35-character reality

More than half of opens happen on mobile, where roughly 35 characters of your subject survive. The length analyzer renders that cut for Gmail app, Outlook, Yahoo, Apple Mail and Gmail web, and the inbox preview adds the preheader line beneath it — the 40–100 characters of free persuasion most senders leave to 'View this email in your browser'.

Guides that use these tools

Best subject lines for cold emails How to write email subject lines Email subject line examples by scenario Email spam words to avoid