Agent-to-Agent Protocol (A2A)

A protocol for AI agent identity, discovery, and communication using the agent:// URI scheme.

Overview

The A2A protocol gives AI agents:

1. Identity — Each agent gets a unique URI: agent://name
2. Discovery — Resolve any agent URI to its endpoint and capabilities
3. Communication — Structured message exchange between agents

URI Scheme

agent://name

• Scheme: agent:// (always lowercase)
• Name: 2-50 characters, lowercase alphanumeric + hyphens
• No trailing slash
• IDN standard for internationalized names

Examples

agent://search        — Search and discovery service
agent://assistant     — General-purpose assistant
agent://code-reviewer — Code review agent

Resolution

An agent URI resolves to an endpoint via DNS lookup:

GET https://marketplace.agenium.net/lookup/{name}

Response:
{
  "success": true,
  "data": {
    "agentUri": "agent://search",
    "endpoint": "https://search.example.com",
    "capabilities": ["search", "discovery"],
    "metadata": {
      "name": "Search Engine",
      "version": "0.1.0"
    }
  }
}

Authentication

Agents authenticate using API keys issued by the marketplace:

X-API-Key: dom_<64 hex characters>

Keys are:

• SHA-256 hashed before storage
• Scoped to exactly one domain
• Rotatable without downtime
• Validated via /credentials/validate endpoint

Agent Card

Every agent service should expose /.well-known/agent.json:

{
  "name": "AGENIUM Search",
  "version": "0.1.0",
  "protocol": "a2a/0.1",
  "agentUri": "agent://agenium",
  "capabilities": ["search", "discovery", "ranking"],
  "endpoints": {
    "search": "GET /search?q={query}",
    "faceted": "GET /search/faceted?q={query}"
  },
  "authentication": {
    "type": "api-key",
    "header": "X-API-Key",
    "obtainAt": "https://marketplace.agenium.net"
  }
}

Registration Flow

1. Register a domain at marketplace.agenium.net
2. Purchase completes → API key is generated
3. Configure your agent's endpoint via API
4. Discoverable — other agents can now resolve your URI

Ecosystem

Status

v0.1 — Alpha

The protocol is functional but evolving. Current limitations:

• Single DNS resolver (marketplace)
• No agent reputation system yet
• mTLS optional (not enforced)

License

MIT