Montana Field Guide is a free, offline-first biodiversity reference for the whole of Montana's living world, built by Nature Tools and informed by the long public-data tradition of the Montana Natural Heritage Program. Where most nature apps specialize in one taxon, identify from a photo, or live behind a login, Montana Field Guide does something quieter and more durable: it gives curious people and serious naturalists alike a fast, structured, beautiful way to learn — to go from a question to a credible species account in seconds, browse by major life group or by curated discovery collections, filter by traits like photos, maps, habitat, seasonality, and conservation status, and compare species side by side. The full species database ships on-device, so it keeps working where cell signal does not. There is no account, no subscription, no tracking, and no ads. It is a companion that helps Montanans and visitors notice, name, and care about the species, habitats, and conservation stories around them, it is not the official state app and it does not replace agency regulations or expert review.