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SLA Uptime Calculator vs Userstack

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

APISLA Uptime CalculatorNEW—UserstackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — limits not publishedFree tier — API key required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

SLA Uptime Calculator vs Userstack: common questions

Which is more reliable, SLA Uptime Calculator or Userstack?

On our scheduled checks, Userstack leads on measured uptime — SLA Uptime Calculator at —% versus Userstack 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 SLA Uptime Calculator and Userstack need an API key?

SLA Uptime Calculator needs no key, while Userstack requires a free API key. If you want to start calling without signup, reach for SLA Uptime Calculator first.

Can I call SLA Uptime Calculator and Userstack from the browser?

Yes — both SLA Uptime Calculator and Userstack 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 SLA Uptime Calculator and Userstack free for commercial use?

SLA Uptime Calculator has unclear commercial terms, and Userstack 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.