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caldays vs Resend

Same instrument, two spec sheets — measured, not claimed.

APIcaldaysNEW—ResendNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — limits not publishedFree tier — API key required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

caldays vs Resend: common questions

Which is more reliable, caldays or Resend?

On our scheduled checks, Resend leads on measured uptime — caldays at —% versus Resend at —% over 90 days. These are our own probe results, not provider claims; the uptime bars above show the day-by-day record for both.

Do caldays and Resend need an API key?

caldays needs no key, while Resend requires a free API key. If you want to start calling without signup, reach for caldays first.

Can I call caldays and Resend from the browser?

Only caldays is browser-friendly — it returns CORS headers over HTTPS. Resend needs a server-side call or proxy, so factor that into which one fits a front-end project.

Are caldays and Resend free for commercial use?

caldays has unclear commercial terms, and Resend has unclear commercial terms. We track service terms and the data license as separate fields — see the Commercial use and Data license rows above, and confirm both before shipping either in a paid product.