Free tools
Tools for people who run newsletters
Check your domain against Gmail and Yahoo’s rules, find out whether an A/B test actually has a winner, and see how long your subscribers really stay. Each runs in your browser — no account, nothing stored.
Bulk sender check
Is your domain ready for Gmail and Yahoo’s sender rules?
Check a sending domain’s SPF, DKIM, DMARC and MX records against the authentication rules Gmail and Yahoo enforce for bulk senders — with a plain-English fix for anything missing.
Open the tool →A/B test calculator
Did that creative really win, or is it noise?
Compare two sponsor creatives or subject lines and find out whether the gap is real — with confidence intervals, a p-value, and how many more impressions an inconclusive test needs.
Open the tool →Subscriber lifetime calculator
How long do your subscribers really stay?
Drop in a subscriber export and get your list’s survival curve: median lifetime and retention at 90, 180 and 365 days. Your file never leaves your browser.
Open the tool →