What is an agent card (A2A)?
A JSON document, served at /.well-known/agent-card.json, that describes an AI agent for the Agent2Agent (A2A) protocol: its name, skills, interfaces, capabilities and authentication.
A2A lets agents built by different vendors delegate tasks to each other. Another agent reads the card to learn what the agent can do and how to call it. Required fields in the A2A specification include name, description, version, supportedInterfaces, capabilities, defaultInputModes, defaultOutputModes and skills; securitySchemes describes how to authenticate.
MCP and A2A solve different problems: MCP connects a model to tools, A2A connects one agent to another.
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Related terms
- Model Context Protocol (MCP)An open protocol, introduced by Anthropic in November 2024, that lets AI applications connect to external tools and data through a standard interface.
- llms.txtA proposed Markdown file at /llms.txt that gives AI models a short, curated map of a website: a title, a one-paragraph summary and lists of key links.