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mailboxlayer vs The Calendar

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

APImailboxlayerUNMONITORED—The CalendarNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeynone
CORSnoyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified (US federal list per 5 U.S.C. § 6103)
Free tierFree tier — key may be requiredFree, no auth (per site)
Rate limitUnpublishedNone stated (site advertises no rate limit)
In directory since2026-07-052026-07-05
operationalpartialdownno data

mailboxlayer vs The Calendar: common questions

Which is more reliable, mailboxlayer or The Calendar?

Only The Calendar is on our probe schedule so far (—% uptime over 90 days). The other is catalogued but not yet live-checked, so we can't compare measured reliability head-to-head — check the uncovered API's own status page for now.

Do mailboxlayer and The Calendar need an API key?

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

Can I call mailboxlayer and The Calendar from the browser?

Only The Calendar 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 mailboxlayer and The Calendar free for commercial use?

mailboxlayer has unclear commercial terms, and The Calendar 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.