# Step 4 — the A2A agent card

/.well-known/agent-card.json describes your agent to other agents: name, skills, endpoints, auth, and declared protocol extensions. Declare extensions with their canonical lowercase URIs — an undeclared extension reads as ‘found but not advertised’ and fails.

Canonical: https://robauto.ai/learn/advanced-agentic-commerce/6

_Advanced Agentic Commerce: Ship the Full Agent Surface — lesson 6 of 20 (DEFINITION)_

/.well-known/agent-card.json describes your agent to other agents: name, skills, endpoints, auth, and declared protocol extensions. Declare extensions with their canonical lowercase URIs — an undeclared extension reads as ‘found but not advertised’ and fails.

Source: [A2A Protocol](https://a2a-protocol.org?utm_source=robauto)

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Machine surfaces: https://robauto.ai/llms.txt · https://robauto.ai/llms-full.txt · https://robauto.ai/.well-known/api-catalog