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Postcodes.io vs Zipcodestack

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

APIPostcodes.ioNEW—ZipcodestackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseService MIT-licensed; postcode data license unverifiedUnverified
Free tierFree — no key requiredFree tier — API key required
Rate limitUnpublished (no key; fair use)Unpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

Postcodes.io vs Zipcodestack: common questions

Which is more reliable, Postcodes.io or Zipcodestack?

On our scheduled checks, Zipcodestack leads on measured uptime — Postcodes.io 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 Postcodes.io and Zipcodestack need an API key?

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

Can I call Postcodes.io and Zipcodestack from the browser?

Yes — both Postcodes.io 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 Postcodes.io and Zipcodestack free for commercial use?

Postcodes.io 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.