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Crossref Metadata Search vs KDP Intelligence

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

APICrossref Metadata SearchHEALTHY90KDP IntelligenceHEALTHY93
Uptime · 30d
Uptime · 90d97.1%97.1%
Uptime · 30d95.0%96.7%
P50 · ms522429
P95 · ms26833902
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Rate limit5 requests/second, 1 concurrent (public pool, per X-Rate-Limit headers)Unpublished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?

Both are neck-and-neck — Crossref Metadata Search and KDP Intelligence each measure 97.1% 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, Crossref Metadata Search or KDP Intelligence?

KDP Intelligence has the lower median latency in our checks — Crossref Metadata Search responds in 522 ms versus KDP Intelligence at 429 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 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.