OpenASN classifies where an IP address is really coming from — residential ISP, mobile carrier, hosting/datacenter, VPN, Tor exit, iCloud Private Relay, enterprise gateway, business, education, government, CGNAT, or unknown — entirely offline, in microseconds, with zero runtime dependencies and zero API calls. It bundles a seed of the open OpenASN dataset (CC0), refreshes it nightly from GitHub Releases, and layers fast-moving overlays (Tor exits, cloud ranges, Apple Private Relay) fetched by your own server from the original authorities. Verdict-first API with full explainability: every classification is auditable to its source.