zat is a Zig library of AT Protocol building blocks that covers identifier parsing, handle and DID resolution, DAG-CBOR and CAR codecs, Merkle Search Tree operations, crypto and key handling, full repo verification, firehose and Jetstream clients, XRPC requests, and JSON extraction helpers. It is designed as a reusable low-level toolkit for building AT Protocol applications, validators, and infrastructure in Zig rather than a single high-level monolithic client.