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IsItWater vs Postcodes.io

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

APIIsItWaterNEW—Postcodes.ioNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeynone
CORSnoyes
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedService MIT-licensed; postcode data license unverified
Free tierFree tier — API key requiredFree — no key required
Rate limitUnpublishedUnpublished (no key; fair use)
In directory since2026-07-052026-07-05
operationalpartialdownno data

IsItWater vs Postcodes.io: common questions

Which is more reliable, IsItWater or Postcodes.io?

On our scheduled checks, Postcodes.io leads on measured uptime — IsItWater at —% versus Postcodes.io 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 IsItWater and Postcodes.io need an API key?

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

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

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

Are IsItWater and Postcodes.io free for commercial use?

IsItWater has unclear commercial terms, and Postcodes.io 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.