A2A Capabilities — How Agents Advertise What They Can Do

Why it matters

Capabilities are how agents find each other in a multi-agent ecosystem. Getting the descriptions right enables correct routing; getting them wrong wastes calls or produces wrong answers.

The architecture

Document location: /.well-known/agent.json. Standard path across A2A agents.

Content: metadata (name, description), skills (each with name, description, input/output schemas), auth methods, supported protocol versions.

How it works end to end

Skill descriptions: natural language explaining what the skill does, when to use it, expected inputs and outputs.

Input/output schemas: JSON Schema for structured messages. Enables validation before invocation.

Discovery: index of agent URLs; routing agent fetches capabilities from each and matches to task.