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Lookup.im API vs Open Library

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

APILookup.im APIUNMONITORED—Open LibraryHEALTHY—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeynone
CORSnoyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedMixed — mostly open
Free tierFree tier — API key requiredUnlimited within courtesy limits
Rate limitUnpublishedSoft — identified UA appreciated
In directory since2026-07-052026-05-02
operationalpartialdownno data

Lookup.im API vs Open Library: common questions

Which is more reliable, Lookup.im API or Open Library?

Only Open Library is on our probe schedule so far (—% uptime over 90 days). The other is catalogued but not yet live-checked, so we can't compare measured reliability head-to-head — check the uncovered API's own status page for now.

Do Lookup.im API and Open Library need an API key?

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

Can I call Lookup.im API and Open Library from the browser?

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

Are Lookup.im API and Open Library free for commercial use?

Lookup.im API 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.