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Free Public APIs API vs Open Library

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

APIFree Public APIs APIUNMONITORED—Open LibraryHEALTHY—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedMixed — mostly open
Free tierFree — limits not publishedUnlimited within courtesy limits
Rate limitUnpublishedSoft — identified UA appreciated
In directory since2026-07-052026-05-02
operationalpartialdownno data

Free Public APIs API vs Open Library: common questions

Which is more reliable, Free Public APIs 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 Free Public APIs API and Open Library need an API key?

Neither needs a paid key — Free Public APIs API 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 Free Public APIs API and Open Library from the browser?

Yes — both Free Public APIs API 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 Free Public APIs API and Open Library free for commercial use?

Free Public APIs 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.