A2A Protocol

Overview

The Agent2Agent (A2A) protocol lets agents built on different frameworks discover each other through an Agent Card, exchange messages, and run long-lived tasks without exposing their internals. The current spec is 1.0 (a2a-protocol.org/v1.0.0/specification) with three bindings: JSON-RPC 2.0 over HTTP, HTTP+JSON/REST and gRPC; streaming uses SSE and async work can use webhook push notifications. This skill was checked against a2a-sdk 1.2.1 (Python) and @a2a-js/sdk 1.3.0.

Most tutorials online still show the 0.2/0.3 API (A2AStarletteApplication, TextPart, /.well-known/agent.json, A2AClient). Those no longer exist in 1.x. If a project pins a2a-sdk<1, follow the SDK's v0.3 to v1.0 migration guide (docs/migrations/v1_0 in the a2a-python repo) rather than mixing styles.

Instructions

1. Core concepts (v1.0)

• Agent Card: JSON served at /.well-known/agent-card.json. Lists name, version, supportedInterfaces (one entry per transport: protocolBinding JSONRPC, HTTP+JSON or GRPC, plus url), capabilities, skills and security schemes. There is no top-level url any more.
• Task: stateful unit of work. States: TASK_STATE_SUBMITTED, WORKING, INPUT_REQUIRED, AUTH_REQUIRED, COMPLETED, FAILED, CANCELED, REJECTED.
• Message: one turn with role (ROLE_USER / ROLE_AGENT) and parts. A Part is a single unified type with text, raw (bytes), url or data; the old TextPart/FilePart/DataPart wrappers are gone.
• Artifact: output of a task (documents, files, structured data).
• Enum names in the SDKs are SCREAMING_SNAKE_CASE (TaskState.TASK_STATE_WORKING, Role.ROLE_USER).

2. Install