What a house reef is
It is the reef around or near the resort island that guests can reach without a boat. Quality, depth and distance from the shore vary a lot between resorts.
Questions worth asking
Can I walk in from the beach, or only from a jetty?
How far is the reef from the shore, and are there currents I should know about?
Is snorkelling kit included, and is there a guided session?
Conditions change
Reef health and visibility vary by year and season. A resort's own recent photos and guest snorkelling reports are better guides than a general reputation.
Resorts with a lively reef are not always the ones with the calmest, whitest lagoon, so decide which matters more.