A2A SDK is a developer toolkit for building, chaining, and managing AI agents in Python. It provides APIs to define agent behaviors via prompts or code, connect agents into pipelines or workflows, and enable asynchronous message passing. Integrations with OpenAI, Llama, Redis, and REST services allow agents to fetch data, call functions, and store state. A built-in UI monitors agent activity, while the modular design ensures you can extend or replace components to fit custom use cases.