A2A Provider + Consumer Pair

This playbook stands up two mono-agents that talk to each other over the Agent-to-Agent (A2A) protocol: agent A publishes an Agent Card with bearer auth (the provider), and agent B discovers and calls it (the consumer). A2A is loaded through channels.plugins[]; the provider side is config-driven, while the consumer side stores its settings in plugin config but invokes remote agents programmatically.

Who this is for

Platform integrators connecting two agents over A2A.

Goal

Publish agent A as an A2A provider (Agent Card discovery, bearer) and configure agent B to discover and call it as a consumer.

Features used

a2a.provider — A2A provider with Agent Card discovery, JSON-RPC + REST, streaming, optional bearer (channels.plugins[] config).
a2a.consumer — calling remote A2A agents (discovery + sendMessage); settings live in plugin config, invocation is code via createA2AConsumerResponder / sendA2AMessage.
channel.plugins — external channel packages loaded by name.

Configuration

The block below is a single mono-agent.config.json carrying both sides for illustration; in practice the provider keys go in agent A’s plugin entry and the consumer keys go in agent B’s plugin entry. The provider keys are plugin config.provider, config.agent, and config.skill; the consumer keys are plugin config.consumer.

Put the provider token in agent A’s .env as MONO_AGENT_A2A_BEARER_TOKEN and the consumer token in agent B’s .env as MONO_AGENT_A2A_CONSUMER_BEARER_TOKEN. The source-config example omits both credentials.

{
  "channels": {
    "plugins": [
      {
        "package": "@mono-agent/a2a-adapter",
        "id": "a2a",
        "config": {
          "enabled": true,
          "provider": {
            "host": "127.0.0.1",
            "port": 4201,
            "requireBearer": true,
            "idempotency": {
              "namespace": "research-production",
              "retentionMs": 2592000000,
              "maxRecords": 10000
            }
          },
          "agent": {
            "name": "Research Agent",
            "description": "Does research.",
            "version": "0.1.0"
          },
          "skill": {
            "id": "research",
            "name": "Research",
            "description": "Web research",
            "tags": ["research"]
          },
          "consumer": {
            "remoteAgentUrls": ["http://127.0.0.1:4201"],
            "defaultRemoteAgentUrl": "http://127.0.0.1:4201",
            "timeoutMs": 30000
          }
        }
      }
    ]
  }
}

Keep bearer tokens out of the file by supplying them via env vars: MONO_AGENT_A2A_BEARER_TOKEN maps to plugin config.provider.bearerToken, and MONO_AGENT_A2A_CONSUMER_BEARER_TOKEN maps to plugin config.consumer.bearerToken. MONO_AGENT_A2A_ENABLED=true maps to plugin config.enabled (the legacy MONO_AGENT_A2A_PROVIDER_ENABLED / config.provider.enabled form is still honored; the root flag wins when both are set). The idempotency namespace is a reviewed stable authenticated-principal boundary, not a URL, version, or secret. See the environment-variable reference.

Steps

Provider: run mono-agent init, add an @mono-agent/a2a-adapter entry under channels.plugins[] with config.provider, config.agent, and config.skill, set requireBearer: true plus MONO_AGENT_A2A_BEARER_TOKEN in .env, and choose a stable provider.idempotency.namespace for paid/non-repeatable work; then mono-agent validate and mono-agent start.
Confirm the Agent Card is reachable at the provider port (e.g. http://127.0.0.1:4201).
Consumer: configure plugin config.consumer.remoteAgentUrls (and defaultRemoteAgentUrl/timeoutMs) plus MONO_AGENT_A2A_CONSUMER_BEARER_TOKEN in .env, or compose createA2AConsumerResponder programmatically — invoking remote agents is code-only, see the programmatic A2A consumer guide.
From the consumer, send text to the provider’s Agent Card URL with the bearer token and the existing logical dispatch id as idempotencyKey (or resolve it with idempotencyKeyForRequest).
Repeat the same keyed call and confirm the provider returns the same task/result without a second responder invocation.