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ClinicalTrials.gov vs NPPES

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

APIClinicalTrials.govHEALTHY78NPPESHEALTHY94
Uptime · 30d
Uptime · 90d100%100%
Uptime · 30d100%100%
P50 · ms138366
P95 · ms35332071
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?

Both are neck-and-neck — ClinicalTrials.gov and NPPES 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, ClinicalTrials.gov or NPPES?

ClinicalTrials.gov has the lower median latency in our checks — ClinicalTrials.gov responds in 138 ms versus NPPES at 366 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 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.