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Open Library vs WhoisXML API Email Verification API

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

APIOpen LibraryHEALTHY—WhoisXML API Email Verification APINEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesyes
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 WhoisXML API Email Verification API: common questions

Which is more reliable, Open Library or WhoisXML API Email Verification API?

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

Open Library needs no key, while WhoisXML API Email Verification 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 WhoisXML API Email Verification API from the browser?

Yes — both Open Library and WhoisXML API Email Verification API 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 Open Library and WhoisXML API Email Verification API free for commercial use?

Open Library has unclear commercial terms, and WhoisXML API Email Verification 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.