Tidy
Never miss a low tide worth exploring: set an alarm for a location and the sea life you're hoping to find, and it schedules a notification ahead of the next low tide that's good enough to spot it.
A free tier that's actually free, at any scale
US tide lookups go straight from the device to NOAA's public data, location search uses the phone's own native geocoder, and the sea-life matching logic runs entirely offline — none of it touches a server, so the default experience costs nothing no matter how many people use it.
Paid coverage stays optional and gated
An optional server only exists to cover coastlines outside NOAA's range, calling paid tide providers on the app's behalf so their API keys never ship inside the public app bundle — keeping a key client-side would let anyone extract it and run up the bill.
Caching shaped around real usage
The optional server's cache key is a coarse location grid plus the calendar day, with in-flight de-duplication, so ten people checking the same town on the same day cost one upstream API call rather than ten.
An interactive shore, not a list
Instead of a plain species list, an interactive cross-section shows five rocky-shore zones with real intertidal species — dragging the tide line crossfades each creature from a dark silhouette to full color as its zone becomes exposed, and tapping one opens a specimen sheet with its tide band and a field note.