VI · Multi-AgentEmerging★

Inter-Agent Communication

also known as A2A, Agent-to-Agent Protocol

Define a protocol for agents to exchange tasks, capabilities, and results across process or vendor boundaries.

This pattern helps complete certain larger patterns —

  • used-byCommunicative Dehallucination★— When an instructed agent would have to invent missing context to comply, have it reverse roles and ask the instructor for the missing detail before answering.
  • used-byCross-Domain Enterprise Agent Network★— Decompose enterprise agency into domain-specialised agents (finance, supply chain, HR, service), each grounded in its own system of record, and route artefacts between them through a standardised inter-agent protocol.

Context

An organisation has agents built by different teams or bought from different vendors — a legal review agent from one supplier, an HR agent from another, an internal IT agent — and they need to cooperate on workflows that cross their boundaries. Each agent speaks a different internal shape: different request envelopes, different result formats, different auth.

Problem

Wiring each pair of agents together with bespoke integration code does not scale. Every new agent forces fresh glue against every other agent it might talk to, and every change to one side breaks the others. There is no shared catalogue of what each agent can do, no shared auth story, and no shared way to version the request envelopes. The cost of adding the fourth or fifth agent becomes prohibitive long before the organisation has the agent population it wanted.

Forces

  • Capability discovery: how does agent A know what agent B can do?
  • Auth and trust across organisational boundaries.
  • Versioning: protocols evolve faster than legacy agents.

Example

An enterprise has agents from three vendors — a legal review agent from one, an HR agent from another, an internal IT agent — and every cross-agent integration is bespoke glue maintained by a different team. They adopt MCP as the inter-agent-communication protocol: each agent advertises its capabilities in a typed envelope, clients discover and invoke without knowing the implementation, and auth flows through one shared mechanism. Adding a fourth vendor's procurement agent now takes a day instead of a quarter.

Diagram

Solution

Therefore:

Adopt a protocol (Google A2A, Anthropic MCP, in-house equivalents) that covers capability advertisement, task delegation, result return, and auth. Agents advertise capabilities; clients discover and invoke; results round-trip in typed envelopes.

What this pattern forbids. Agents may only invoke each other through the advertised protocol; out-of-band calls are forbidden.

The smaller patterns that complete this one —

  • generalisesActor-Model Agents★— Implement each agent as an independent actor with its own mailbox, processing asynchronous messages one at a time and never sharing mutable state with peers.
  • generalisesTopic-Based Routing★— Route inter-agent messages through named topics that agents subscribe to, instead of having senders address each other by id.

And the patterns that stand alongside it, or against it —

  • complementsModel Context Protocol★★— Standardise how agents discover and call tools so that a tool written once is usable by any conformant agent.
  • composes-withHandoff★— Transfer the active conversation from one agent to another, carrying context across the switch.
  • complementsSupervisor★★— Place a coordinating agent above a set of specialised agents and route work to them.
  • complementsOrchestrator-Workers★★— An orchestrator dynamically breaks a task into subtasks at runtime and delegates each to a worker LLM, then synthesises results.
  • composes-withTool/Agent Registry★— Maintain a single queryable catalogue of both available tools and available agents, with metadata (capability, cost, latency, quality) the agent can use to pick the right one for a task.
  • alternative-toDecentralized Agent Network·— Agents publish signed DID+JSON-LD identity records so any peer can discover and verify them without a central registry — the agent equivalent of the open web.
  • complementsAgent Capability Manifest★— Let each agent publish a standardized self-description — identity, skills, endpoint, and auth needs — at a well-known location, so others discover it and bind by capability at runtime instead of through hardcoded coupling.
  • complementsAgent-Initiated Payment★— Give an agent a bounded wallet so it can settle a payment mid-request to unlock a resource — answering a payment-required challenge with a verifiable proof — instead of routing every purchase through a human.

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References

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