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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.

A2A (Agent2Agent protocol): mentions per chapter4 mentions of the term across 1 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapter23 AI Agents: 4 mentions23 AI Agents4No mentions in the other 22 chaptersSource: the Body of Knowledgev0.5.0
A2A (Agent2Agent protocol): mentions per chapter4 mentions of the term across 1 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapter0001020304050607081011121314151617181920212223 AI Agents: 4 mentions423Source: the Body of Knowledge v0.5.0
Mentions per chapter How often each chapter names the term, with the chapters the glossary cross-references drawn solid. The longest bar is where to read the term in use; bars spread across many chapters mark a term that runs through the discipline.
Mentions as a table
Mentions of A2A (Agent2Agent protocol) per chapter
ChapterMentionsCross-referenced
00 Preface0No
01 Definition0No
02 Why Now0No
03 Values & Principles0No
04 The Stack0No
05 Patterns0No
06 The Role0No
07 Maturity Model0No
08 Regulatory Map0No
10 Reading List0No
11 AI Defined0No
12 Governance Program0No
13 Risk Management0No
14 Development0No
15 Deployment0No
16 Fairness & XAI0No
17 Incidents0No
18 EU AI Act0No
19 Privacy & AI0No
20 Existing Law0No
21 AI Laws Worldwide0No
22 Principles & Standards0No
23 AI Agents4Yes
A2A (Agent2Agent protocol): related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastA2A (Agent2Agent protocol)Related terms (2)Agent (agentic AI) · RelatedAgent (agentic AI)Agent Card · RelatedAgent CardContrast with (1)MCP · ContrastMCP
A2A (Agent2Agent protocol): related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastRelated terms (2)Agent (agentic AI) · RelatedAgent (agentic AI)Agent Card · RelatedAgent CardContrast with (1)MCP · ContrastMCPA2A(Agent2Agentprotocol)
The term's neighbourhood Terms related to this one on solid edges, terms it is often confused with on dashed edges, and the patterns that use it most in the colour of their layer. Follow a dashed edge to check the distinction before you use either term.
Neighbourhood as a table
Neighbourhood of A2A (Agent2Agent protocol)
FamilyItemRelation
Related termsAgent (agentic AI)Related
Related termsAgent CardRelated
Contrast withMCPContrast
  • 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}
}