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Callook.info vs Open Library

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

APICallook.infoNEW—Open LibraryHEALTHY—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverified (data from public FCC ULS records)Mixed — mostly open
Free tierFree — limits not publishedUnlimited within courtesy limits
Rate limitUnpublishedSoft — identified UA appreciated
In directory since2026-07-052026-05-02
operationalpartialdownno data

Callook.info vs Open Library: common questions

Which is more reliable, Callook.info or Open Library?

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

Neither needs a paid key — Callook.info is callable with no signup, and Open Library is callable with no signup. Both are quick to prototype with; rate limits still apply.

Can I call Callook.info and Open Library from the browser?

Yes — both Callook.info and Open Library send CORS headers over HTTPS, so front-end code can fetch either directly with no backend proxy. That makes them easy to swap in a client-side app while you compare responses.

Are Callook.info and Open Library free for commercial use?

Callook.info has unclear commercial terms, and Open Library 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.