A2A Protocol
Open protocol letting AI agents discover each other and collaborate over HTTP, JSON-RPC, and SSE.
About
A2A (Agent2Agent) is an open protocol for interoperability between AI agents built on different frameworks by different vendors. Agents publish an Agent Card describing their capabilities, and clients invoke them as tasks over HTTP with JSON-RPC, with optional server-sent-events streaming and push notifications for long-running work.
The key idea is opaque collaboration: agents coordinate on tasks without exposing internal tools, memory, or reasoning. Launched by Google in April 2025 and now stewarded under the a2aproject organization with broad industry participation, it complements MCP (which connects agents to tools) by connecting agents to agents. The spec and reference SDKs are Apache-2.0, and framework adapters exist for LangGraph, CrewAI, Genkit, and others.
What it can do
- Agent Cards for capability discovery across vendors
- Task-based messaging over HTTP/JSON-RPC with SSE streaming
- Negotiated interaction modalities (text, forms, media)
- Long-running tasks with push notifications and human-in-the-loop
- Open spec with Python and JS/TS reference SDKs
Setup
Read the spec at a2aproject.github.io/A2A, publish an Agent Card JSON for your agent, and use the a2a-sdk (Python/JS) to serve or call remote agents.
Prerequisites
An agent with an HTTP endpoint; familiarity with JSON-RPC helps.
Use cases
Works with
Trust score — 9/10
Scored 9/10 (verified tier, metrics-v1). Evidence: 26,164 GitHub stars (a2aproject/A2A); repo pushed 2026-10-15 (same-day activity); Apache-2.0 license confirmed in repo; launched by Google Apr 2025, now stewarded by a2aproject org; officialUrl https://a2aproject.github.io/A2A/ curl-verified 200 (old google-a2a.github.io URL now 404). Manual review: Agent Card/JSON-RPC/SSE/push-notification mechanics verified against official spec; MCP-complementary framing is the project's stated positioning. License: Apache-2.0.
★ 26,164 GitHub stars
Sources
Every fact above was checked against these sources. Where a claim comes from the provider and couldn't be independently verified, the text says so.