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Open Library vs Registrum API

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

APIOpen LibraryHEALTHY—Registrum APINEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseMixed — mostly openUnverified
Free tierUnlimited within courtesy limitsFree tier — API key required
Rate limitSoft — identified UA appreciatedUnpublished
In directory since2026-05-022026-07-05
operationalpartialdownno data

Open Library vs Registrum API: common questions

Which is more reliable, Open Library or Registrum API?

On our scheduled checks, Registrum API leads on measured uptime — Open Library at —% versus Registrum API 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 Open Library and Registrum API need an API key?

Open Library needs no key, while Registrum API requires a free API key. If you want to start calling without signup, reach for Open Library first.

Can I call Open Library and Registrum API from the browser?

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

Are Open Library and Registrum API free for commercial use?

Open Library has unclear commercial terms, and Registrum API 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.