The verification layer for newsletter metrics.
LetterSignal provides API-verified, publicly shareable newsletter metrics — so sponsors can trust the numbers, and publishers never have to explain them again.
Free verification. Automatic updates. Public by default.
Built for publishers who sell sponsorships directly — and sponsors who need real data.
A public standard for newsletter metrics
Newsletter sponsorship runs on trust — but today that trust is built on PDFs, screenshots, and stale numbers. LetterSignal replaces that with a single, public source of truth:
How it works
Connect your newsletter
Securely connect your email platform to enable API-verified metrics.
We verify and update
Subscriber count, open rate, and engagement are pulled automatically and refreshed monthly.
Share one link
Send sponsors a single public page that always reflects your latest verified data.
What's included (free)
- API-verified newsletter metrics
- Monthly automatic updates
- Public, shareable verification page
- "Verified" badge sponsors recognize
- Standard media kit export
No manual updates. No screenshots. No PDFs going stale.
Browse verified newsletters
LetterSignal maintains a public directory of verified publications — creating a shared standard sponsors can reference and trust.
Explore the directoryWhy sponsors trust LetterSignal
When metrics are verifiable, deals close faster.
Advanced analytics, benchmarking, and sponsor discovery tools are coming for publishers who want deeper insight.