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ClinicalTrials.gov vs NPPES

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

APIClinicalTrials.govNEW—NPPESNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearyes
Data licenseUnverifiedU.S. Government (public NPI data)
Free tierFree — limits not publishedFree — no key required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

ClinicalTrials.gov vs NPPES: common questions

Which is more reliable, ClinicalTrials.gov or NPPES?

On our scheduled checks, NPPES leads on measured uptime — ClinicalTrials.gov at —% versus NPPES 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 ClinicalTrials.gov and NPPES need an API key?

Neither needs a paid key — ClinicalTrials.gov is callable with no signup, and NPPES is callable with no signup. Both are quick to prototype with; rate limits still apply.

Can I call ClinicalTrials.gov and NPPES from the browser?

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

Are ClinicalTrials.gov and NPPES free for commercial use?

ClinicalTrials.gov has unclear commercial terms, and NPPES allows commercial use on its free tier. 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.