A2A Protocol
A2A is an open protocol for agent-to-agent communication. The GitHub repo is github.com/a2aproject/A2A (25,373 stars, Apache-2.0; google/A2A redirects there). The site footer says Copyright 2026 The Linux Foundation and Apache-2.0. Docs still describe Agent Cards, tasks, messages, and complementarity with MCP. The spec is $0. Drop the leftover 50+ partners list unless a first-party page still prints those names today.
Compare LangChain if you wanted an MIT library, and Cline if you wanted an agent product rather than a protocol.
Key Features
- Agent Cards: JSON capability ads so other agents can find you. Confirm the current card schema in the spec.
- Tasks and messages: Stateful work units over HTTP + SSE. That is the protocol, not a hosted product.
- Complements MCP: Docs say MCP is tools; A2A is agent-to-agent. They are not competitors.
- Not a chat app: The spec says it is machine-to-machine, not Slack/Discord.
Use Cases
- Teams exposing an agent that other vendors should call without sharing internals.
- People comparing A2A vs MCP: use both if you need tools and delegation.
- People who wanted a SaaS seat: there is no A2A Cloud $N.
Limitation: Partner logos and "industry standard" claims were not re-audited as a live census. Quote the spec and the star count we fetched.
Pricing
No product SKU on 2026-08-17.
| Path | Price | Notes |
|---|---|---|
| A2A spec / repo | $0 | Apache-2.0. 25,373 stars. Linux Foundation copyright 2026. |
If a leftover blog still lists a Google-only license or 50 named partners as a contract, treat the spec footer as the source.
Getting Started
- Read a2a-protocol.org/latest.
- Clone a2aproject/A2A, not an old google/A2A bookmark.
- Publish one Agent Card before you promise cross-vendor discovery.
- Confirm MCP if you only needed tools, not agent delegation.
Frequently Asked Questions
Is A2A free?
The protocol is Apache-2.0. Your agents and models are not.
Is it still google/A2A?
That URL redirects to a2aproject/A2A.
Same as MCP?
No. MCP is agent-to-tool. A2A is agent-to-agent.
Alternatives
Tips
- Quote Apache-2.0 and 25,373 stars.
- Do not paste a 50-partner roster into a deck.
- Confirm the live spec version before you implement.
Conclusion
A2A is a $0 Apache-2.0 agent protocol under Linux Foundation copyright, not a partner-logo landing page. Start at a2a-protocol.org/latest, then decide whether you needed MCP tools instead of agent-to-agent calls.
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