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SLF vs Zipcodestack

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

APISLFNEW—ZipcodestackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — static file, no keyFree tier — API key required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

SLF vs Zipcodestack: common questions

Which is more reliable, SLF or Zipcodestack?

On our scheduled checks, Zipcodestack leads on measured uptime — SLF at —% versus Zipcodestack 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 SLF and Zipcodestack need an API key?

SLF needs no key, while Zipcodestack requires a free API key. If you want to start calling without signup, reach for SLF first.

Can I call SLF and Zipcodestack from the browser?

Yes — both SLF and Zipcodestack 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 SLF and Zipcodestack free for commercial use?

SLF has unclear commercial terms, and Zipcodestack 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.