--- schema: formation.pattern/v0.1 kind: pattern visibility: public aliases: - 'peer-to-peer agents' - 'agent network' - 'direct agent messaging' - 'network of agents (LangGraph)' canonical_url: https://topologyindex.com/patterns/mailbox_network.md description: 'Agents address each other through per-agent mailboxes instead of one open board.' executable_here: false executor_requirements: - concurrent_role_invocations - agent_to_agent_messages family: shared_state findings_page: /patterns/mailbox_network/findings.md observed_in: - /research/openai-hugging-face-agent-coordination.md path: /patterns/mailbox_network.md pattern: mailbox_network pattern_index: /patterns/index.md product_api_version: v1 published_findings: - benchmarks: - MATH - GSM8K - MathVista - Anthropic-HH compared_against: 'Fully connected multi-agent debate' direction: helped source_id: arxiv:2406.11776 task_domain: 'Math reasoning, multimodal reasoning and alignment labeling' task_domains: - reasoning - evaluation url: https://arxiv.org/abs/2406.11776 - benchmarks: - MMLU - GSM8K - MultiArith - SVAMP - AQuA - HumanEval compared_against: 'Chain, tree, star, complete, layered and random topologies and frameworks such as AutoGen and GPTSwarm' direction: helped source_id: arxiv:2410.02506 task_domain: 'General, math reasoning and code generation' task_domains: - coding - reasoning url: https://arxiv.org/abs/2410.02506 - benchmarks: - MedQA - PubMedQA - MMLU - CosmosQA - CIAR - GPQA compared_against: 'Self-consistency and ensembling over multiple reasoning paths' direction: no_clear_gain source_id: arxiv:2311.17371 task_domain: 'Medical and general reasoning question answering' task_domains: - reasoning url: https://arxiv.org/abs/2311.17371 - benchmarks: - ECQA - GSM8K - FOLIO-wiki compared_against: 'A single agent with strong prompts and demonstrations' direction: no_clear_gain source_id: arxiv:2402.18272 task_domain: 'Commonsense, math and deductive reasoning' task_domains: - reasoning url: https://arxiv.org/abs/2402.18272 - benchmarks: - MMLU - MATH - 'Chess Move Validity' compared_against: 'Different numbers of agents, rounds and debate or reflection strategies' direction: mixed source_id: arxiv:2310.02124 task_domain: 'Knowledge, math and state-tracking reasoning' task_domains: - reasoning url: https://arxiv.org/abs/2310.02124 - benchmarks: - BrowseComp-Plus - Finance-Agent - PlanCraft compared_against: 'A single agent and centralized, independent and hybrid multi-agent architectures' direction: mixed source_id: arxiv:2512.08296 task_domain: 'Agentic benchmarks spanning finance, web browsing and planning' task_domains: - research - reasoning - operations url: https://arxiv.org/abs/2512.08296 qualifying_evidence: [] references: [] schema_version: v0.1 title: 'When to use the mailbox_network multi-agent pattern (peer-to-peer agents, agent network)?' unmet_executor_requirements: - concurrent_role_invocations - agent_to_agent_messages --- # When to use the mailbox_network multi-agent pattern (peer-to-peer agents, agent network)? **Short answer:** test it only when a common channel has grown too large to scan and most traffic concerns two participants; otherwise start from the [decision guide](/patterns/index.md) row for your task. A hypothesis, not a ranking; [published findings](/patterns/mailbox_network/findings.md) keep the unfavourable ones. The `mailbox_network` multi-agent pattern (family `shared_state`): agents address each other through per-agent mailboxes instead of one open board. Also called: peer-to-peer agents, agent network, direct agent messaging, network of agents (LangGraph). ## The arrangement - Structure: One mailbox per agent; messages are addressed rather than broadcast. - Control: Point to point. A recipient decides when, or whether, to read. - Shared state: Only what a sender leaves in a recipient’s mailbox. ## When it is hypothesised to fit Hypothesised to fit when a common channel has grown too large to scan and most traffic concerns two participants. The record below reports this is how mailboxes appeared there. A hypothesis to test on a workload, not a finding: this service has not tested it. ## Failure modes to watch for - Addressing conventions have to be invented and agreed, and they drift. - A message sits unread if the recipient never comes back; the record below reports a mailbox that received nothing at all. - Sender identity is only as good as the naming convention. - State fragments across mailboxes, so no participant holds the whole picture any more. These are things to watch for, not outcomes anyone measured here. ## What published studies found Attributed to each source and stated without figures; unfavourable results are included on purpose, and none of this is evidence produced by this service. What each was compared with is in `published_findings`; each finding in words, with its caveat, is at [/patterns/mailbox_network/findings.md](/patterns/mailbox_network/findings.md). Reviewed 2026-09-23. Each label says how this pattern fared against what it was compared with, as the source reports it; the labels are defined at [/docs/schemas/pattern/v0.1.md](/docs/schemas/pattern/v0.1.md). - **Helped**: [Improving Multi-Agent Debate with Sparse Communication Topology](https://arxiv.org/abs/2406.11776) - **Helped**: [Cut the Crap: An Economical Communication Pipeline for LLM-based Multi-Agent Systems](https://arxiv.org/abs/2410.02506) - **No clear gain**: [Should we be going MAD? A Look at Multi-Agent Debate Strategies for LLMs](https://arxiv.org/abs/2311.17371) - **No clear gain**: [Rethinking the Bounds of LLM Reasoning: Are Multi-Agent Discussions the Key?](https://arxiv.org/abs/2402.18272) - **Mixed**: [Exploring Collaboration Mechanisms for LLM Agents: A Social Psychology View](https://arxiv.org/abs/2310.02124) - **Mixed**: [Towards a Science of Scaling Agent Systems](https://arxiv.org/abs/2512.08296) ## Can this deployment execute it No. The runner does not provide everything this arrangement needs. What is missing: - `concurrent_role_invocations` (more than one agent acting at the same time): The supervisor runs one invocation at a time and refuses a declared active-agent count above one, rather than serializing a parallel policy and calling it the same thing. - `agent_to_agent_messages` (a channel on which one agent addresses another): The adapter sees a single role invocation, and the tool surface offers no channel to another agent. A topology formation that declares what this deployment cannot run is still stored, and is refused with an unsupported-capability error rather than reduced to a simpler arrangement and run anyway. ## Evidence for this pattern None. No qualifying evidence exists here for this pattern, and by design none ever will: an evidence snapshot is about the complete execution configuration that produced the observations, so the most it can support is a claim about that configuration on that workload. ## Observed in Reports that describe this arrangement. A report is a reason to test an arrangement, never a result for it. - [Agent coordination in the OpenAI and Hugging Face evaluation incident](/research/openai-hugging-face-agent-coordination.md) (descriptive_only) ## How evidence works here A pattern names how work is organized, never how well that works. Evidence in this service attaches to a complete execution configuration — a topology formation together with an execution lock pinning models, tools and runtime — and never to a pattern on its own, so no page here carries a success rate, a cost or a run count for an arrangement.