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ImprovMX API vs PostStack

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

APIImprovMX APINEW—PostStackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeyapiKey
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree tier — API key requiredFree tier — key may be required
Rate limit301 req/window · 300 remaining · resets 1783526520Unpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

ImprovMX API vs PostStack: common questions

Which is more reliable, ImprovMX API or PostStack?

On our scheduled checks, PostStack leads on measured uptime — ImprovMX API at —% versus PostStack 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 ImprovMX API and PostStack need an API key?

Both ask you to authenticate — ImprovMX API uses an API key and PostStack uses an API key. Each key is free to obtain; the Auth and Card-required rows above spell out the signup terms.

Can I call ImprovMX API and PostStack from the browser?

Only ImprovMX API 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 ImprovMX API and PostStack free for commercial use?

ImprovMX API 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.