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caldays vs PostStack

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

APIcaldaysHEALTHY99PostStackHEALTHY87
Uptime · 30d
Uptime · 90d100%100%
Uptime · 30d100%100%
P50 · ms1491066
P95 · ms6751890
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 PostStack: common questions

Which is more reliable, caldays or PostStack?

Both are neck-and-neck — caldays and PostStack 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, caldays or PostStack?

caldays has the lower median latency in our checks — caldays responds in 149 ms versus PostStack at 1066 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 caldays and PostStack need an API key?

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

Can I call caldays and PostStack from the browser?

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

Are caldays and PostStack free for commercial use?

caldays has unclear commercial terms, and PostStack 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.