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caldays vs mailboxlayer

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

APIcaldaysNEW—mailboxlayerNEW—
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 — key may be required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

caldays vs mailboxlayer: common questions

Which is more reliable, caldays or mailboxlayer?

On our scheduled checks, mailboxlayer leads on measured uptime — caldays at —% versus mailboxlayer 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 mailboxlayer need an API key?

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

Can I call caldays and mailboxlayer from the browser?

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

Are caldays and mailboxlayer free for commercial use?

caldays has unclear commercial terms, and mailboxlayer 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.