A2A Protocol¶

Lango supports the A2A protocol for inter-agent communication. This allows a Lango instance to advertise its capabilities via an Agent Card and to discover and integrate external A2A-compatible agents as sub-agents.

Overview¶

The A2A implementation has two sides:

1. Server -- Exposes this Lango agent as an A2A service with a discoverable Agent Card
2. Client -- Discovers and integrates remote A2A agents into the local orchestrator tree

graph LR
    subgraph Local Lango
        O[Orchestrator] --> L[Local Sub-Agents]
        O --> RA[Remote Agent Proxy]
    end

    subgraph Remote Service
        AC[Agent Card<br/>/.well-known/agent.json]
        RS[Remote Agent]
    end

    RA -- "A2A Protocol" --> RS
    RA -. "discovery" .-> AC

    style AC fill:#e67e22,color:#fff
    style RA fill:#e67e22,color:#fff

Agent Card¶

When A2A is enabled, Lango serves an Agent Card at /.well-known/agent.json. The card describes the agent's name, description, URL, and skills.

Card Structure¶

{
  "name": "lango-assistant",
  "description": "Lango AI Assistant",
  "url": "https://your-host:18789",
  "skills": [
    {
      "id": "lango-orchestrator",
      "name": "lango-orchestrator",
      "description": "Lango Assistant Orchestrator",
      "tags": ["orchestration"]
    },
    {
      "id": "operator",
      "name": "operator",
      "description": "System operations: shell commands, file I/O, and skill execution",
      "tags": ["sub_agent:lango-orchestrator"]
    }
  ]
}

Skills are automatically derived from the agent tree. The root agent is listed with the orchestration tag, and each sub-agent is listed with a sub_agent:<parent> tag.

Remote Agents¶

Remote A2A agents are discovered by fetching their Agent Card from a configured URL. Each remote agent is integrated as a sub-agent in the multi-agent orchestrator.

Discovery Process¶

1. Lango fetches the Agent Card from the configured agentCardUrl
2. The ADK remoteagent.NewA2A() creates a proxy agent from the card
3. The proxy is added to the orchestrator's sub-agent list
4. The orchestrator can delegate tasks to the remote agent via transfer_to_agent

Graceful Degradation¶

If a remote agent is unreachable during startup, Lango logs a warning and skips it. The rest of the agent tree continues to function normally. No remote agent failure blocks the startup process.

WARN  load remote agent  name=weather-agent  url=https://weather.example.com/.well-known/agent.json  error=connection refused

Configuration¶

Settings: lango settings → A2A Protocol

{
  "a2a": {
    "enabled": true,
    "baseUrl": "https://your-host:18789",
    "agentName": "lango-assistant",
    "agentDescription": "Lango AI Assistant",
    "remoteAgents": [
      {
        "name": "weather-agent",
        "agentCardUrl": "https://weather.example.com/.well-known/agent.json"
      },
      {
        "name": "code-review-agent",
        "agentCardUrl": "https://review.example.com/.well-known/agent.json"
      }
    ]
  }
}

Each remote agent entry requires:

Setup¶

Enable via Onboard¶

The A2A protocol can be enabled during the interactive onboarding flow:

lango onboard

Select the A2A Protocol option from the feature menu.

Add Remote Agents¶

Remote agents are configured via the config file. Use the config export/edit/import workflow:

# Export current config
lango config export > config.json

# Edit to add remote agents under a2a.remoteAgents
# ...

# Import updated config
lango config import config.json

A2A-over-HTTP vs A2A-over-P2P¶

Lango supports two modes of inter-agent communication:

Both modes can be enabled simultaneously. A2A-over-HTTP is simpler to set up for public agents, while A2A-over-P2P provides stronger security guarantees and works without centralized infrastructure.

See P2P Network for P2P-specific documentation.