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Crossref Metadata Search vs KDP Intelligence

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

APICrossref Metadata SearchNEW—KDP IntelligenceNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useyesunclear
Data licenseOpen Crossref metadata (much is CC0)Unverified
Free tierFree, no key (public pool)Free preview/check endpoints; full niche data is paid via x402 USDC
Rate limit5 requests/second, 1 concurrent (public pool, per X-Rate-Limit headers)Unpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

Crossref Metadata Search vs KDP Intelligence: common questions

Which is more reliable, Crossref Metadata Search or KDP Intelligence?

On our scheduled checks, KDP Intelligence leads on measured uptime — Crossref Metadata Search at —% versus KDP Intelligence 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 Crossref Metadata Search and KDP Intelligence need an API key?

Neither needs a paid key — Crossref Metadata Search is callable with no signup, and KDP Intelligence is callable with no signup. Both are quick to prototype with; rate limits still apply.

Can I call Crossref Metadata Search and KDP Intelligence from the browser?

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

Are Crossref Metadata Search and KDP Intelligence free for commercial use?

Crossref Metadata Search allows commercial use on its free tier, and KDP Intelligence 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.