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Sofiaplan vs Open Library

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

APISofiaplanUNMONITORED—Open LibraryHEALTHY—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
Authnonenone
CORSnoyes
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

Sofiaplan vs Open Library: common questions

Which is more reliable, Sofiaplan 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 Sofiaplan and Open Library need an API key?

Neither needs a paid key — Sofiaplan 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 Sofiaplan and Open Library from the browser?

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

Are Sofiaplan and Open Library free for commercial use?

Sofiaplan 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.