Why this exists

Every ESP has a preview button. None of them tell you your email is about to get clipped by Gmail, or that "100% free" in your third paragraph is about to land you in Promotions instead of the inbox. You find out the hard way — after you've already sent it.

MRNEWSLETTER started as a checklist one newsletter writer kept re-running by hand before every send: check the byte count, scan for the obvious spam words, squint at the subject line on a phone. It got tedious enough to automate, and specific enough that it seemed worth sharing.

The Swap Exchange came from the same place. Cross-promotion swaps are one of the best ways to grow a newsletter, but they fall apart fast when one side has ten times the reach of the other and nobody wants to say so. Verifying reach through the ESP directly — instead of trusting a screenshot — takes the guesswork out.

This is a small, independent tool. It doesn't have a growth team or a Series A — it has two features it tries to do precisely, and a Free tier that's meant to actually be usable, not a 3-day trial in disguise.