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MailboxValidator Free Email Checker vs SLA Uptime Calculator

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

APIMailboxValidator Free Email CheckerHEALTHY94SLA Uptime CalculatorHEALTHY82
Uptime · 30d
Uptime · 90d100%100%
Uptime · 30d100%100%
P50 · ms5271373
P95 · ms11382741
AuthapiKeynone
CORSnoyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree tier — API key requiredFree — limits not published
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

MailboxValidator Free Email Checker vs SLA Uptime Calculator: common questions

Which is more reliable, MailboxValidator Free Email Checker or SLA Uptime Calculator?

Both are neck-and-neck — MailboxValidator Free Email Checker and SLA Uptime Calculator each measure 100% uptime over 90 days on our probe schedule. Reliability here is verified from our own scheduled checks; use the 30-day bars above to see which has been steadier lately.

Which is faster, MailboxValidator Free Email Checker or SLA Uptime Calculator?

MailboxValidator Free Email Checker has the lower median latency in our checks — MailboxValidator Free Email Checker responds in 527 ms versus SLA Uptime Calculator at 1373 ms (P50). Tail latency (P95) is in the table above; for most workloads the median is the number that shapes how the API feels.

Do MailboxValidator Free Email Checker and SLA Uptime Calculator need an API key?

SLA Uptime Calculator needs no key, while MailboxValidator Free Email Checker requires a free API key. If you want to start calling without signup, reach for SLA Uptime Calculator first.

Can I call MailboxValidator Free Email Checker and SLA Uptime Calculator from the browser?

Only SLA Uptime Calculator is browser-friendly — it returns CORS headers over HTTPS. MailboxValidator Free Email Checker needs a server-side call or proxy, so factor that into which one fits a front-end project.

Are MailboxValidator Free Email Checker and SLA Uptime Calculator free for commercial use?

MailboxValidator Free Email Checker has unclear commercial terms, and SLA Uptime Calculator 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.