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mailboxlayer vs The Calendar

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

APImailboxlayerHEALTHY96The CalendarHEALTHY90
Uptime · 30d
Uptime · 90d100%100%
Uptime · 30d100%100%
P50 · ms316588
P95 · ms26343550
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?

Both are neck-and-neck — mailboxlayer and The Calendar each measure 100% uptime over 90 days on our probe schedule. Reliability here is verified from our own scheduled checks; use the 30-day bars above to see which has been steadier lately.

Which is faster, mailboxlayer or The Calendar?

mailboxlayer has the lower median latency in our checks — mailboxlayer responds in 316 ms versus The Calendar at 588 ms (P50). Tail latency (P95) is in the table above; for most workloads the median is the number that shapes how the API feels.

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.