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A2A (Agent2Agent protocol)

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An open protocol for agents to hand tasks to one another, at version 1.0 since March 2026 1 and a Growth Stage project of the Linux Foundation-directed Agentic AI Foundation since August 2026 2. Servers must authenticate every request, but authorisation, and the scope and revocation of authority granted mid-task, are left to the implementer 1.

Developed in
ch. 23, Multi-agent systems and delegation chains
Chapters
ch. 23, AI Agents
Contrast with
MCP
Source
2 numbered references, listed below

Where it is used

One chapter of the Body of Knowledge uses the term. Each link opens the first section that does.

  • Agent Card

    The JSON document an A2A agent publishes, usually at /.well-known/agent-card.json, describing its identity, skills, service endpoint and the authentication…

  • Agent (agentic AI)

    An AI system that acts (browses, executes code, calls APIs, moves data or delegates to other agents) under delegated authority, rather than only producing text.

Sources

  1. [1] Agent2Agent (A2A) Protocol Specification, v1.0 (v1.0.0 released 2026-03-12 and v1.0.1 on 2026-05-28 in github.com/a2aproject/A2A; Agent Card at /.well-known/agent-card.json, signed with JWS over JCS-canonicalised JSON; servers authenticate every request; authorisation implementation-specific; scope and revocation of in-task authorisation not defined). A2A Project (Linux Foundation). 2026-05-28. https://a2a-protocol.org/latest/specification/ (verified: primary)
  2. [2] "A New Chapter for A2A: Joining the Agentic AI Foundation" (A2A accepted as a Growth Stage project of the Linux Foundation-directed Agentic AI Foundation, alongside MCP). A2A Project. 2026-08-27. https://a2a-protocol.org/latest/blog/2026/08/27/a-new-chapter-for-a2a-joining-the-agentic-ai-foundation/ (verified: primary)

Definitions of legal terms paraphrase the cited text, which governs. Dated statements are as of .

Cite this term

García Aibar, J. (2026). A2A (Agent2Agent protocol). In AI Governance Engineering: The Thesis & Body of Knowledge (v0.5.0), Glossary. https://doi.org/10.5281/zenodo.22956197. https://aigovernanceengineer.com/glossary/a2a-agent2agent-protocol. CC BY 4.0

BibTeX

@misc{aige2026a2aagent2agentprotocol,
  author  = {Jorge García Aibar},
  title   = {{A2A (Agent2Agent protocol)}},
  note    = {Glossary, AI Governance Engineering: The Thesis \& Body of Knowledge, version 0.5.0},
  year    = {2026},
  doi     = {10.5281/zenodo.22956197},
  url     = {https://aigovernanceengineer.com/glossary/a2a-agent2agent-protocol}
}