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MailCheck.ai vs OpenHolidays API

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

APIMailCheck.aiNEW—OpenHolidays APINEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — limits not publishedFree — limits not published
Rate limit5 req/window · 4 remainingUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

MailCheck.ai vs OpenHolidays API: common questions

Which is more reliable, MailCheck.ai or OpenHolidays API?

On our scheduled checks, OpenHolidays API leads on measured uptime — MailCheck.ai at —% versus OpenHolidays API 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 MailCheck.ai and OpenHolidays API need an API key?

Neither needs a paid key — MailCheck.ai is callable with no signup, and OpenHolidays API is callable with no signup. Both are quick to prototype with; rate limits still apply.

Can I call MailCheck.ai and OpenHolidays API from the browser?

Yes — both MailCheck.ai and OpenHolidays API send CORS headers over HTTPS, so front-end code can fetch either directly with no backend proxy. That makes them easy to swap in a client-side app while you compare responses.

Are MailCheck.ai and OpenHolidays API free for commercial use?

MailCheck.ai has unclear commercial terms, and OpenHolidays API 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.