choosing-swarm-patterns

Overview

10 orchestration patterns for multi-agent workflows. Pick the simplest pattern that solves the problem — add complexity only when the system proves it's insufficient.

Quick Decision Framework

```

Is the task independent per agent?
  YES → fan-out (parallel workers)

Does each step need the previous step's output?
  YES → Is it strictly linear?
    YES → pipeline
    NO  → dag (parallel where possible)

Does a coordinator need to stay alive and adapt?
  YES → Is there one level of management?
    YES → hub-spoke
    NO  → hierarchical (multi-level)

Is the task about making a decision?
  YES → Do agents need to argue opposing sides?
    YES → debate (adversarial)
    NO  → consensus (cooperative voting)

Does the right specialist emerge during processing?
  YES → handoff (dynamic routing)

Do all agents need to freely collaborate?
  YES → mesh (peer-to-peer)

Is cost the primary concern?
  YES → cascade (cheap model first, escalate if needed)

Pattern Reference

#	Pattern	Topology	Agents	Best For
1	fan-out	Star (SDK center)	N parallel	Independent subtasks (reviews, research, tests)
2	pipeline	Linear chain	Sequential	Ordered stages (design → implement → test)
3	hub-spoke	Star (live hub)	1 lead + N workers	Dynamic coordination, lead reviews/adjusts
4	consensus	Broadcast + vote	N voters	Architecture decisions, approval gates
5	mesh	Fully connected	N peers	Brainstorming, collaborative debugging
6	handoff	Routing chain	1 active at a time	Triage, specialist routing, support flows
7	cascade	Tiered escalation	Cheapest → most capable	Cost optimization, production workloads
8	dag	Dependency graph	Parallel + joins	Complex projects with mixed dependencies
9	debate	Adversarial rounds	2+ debaters + judge	Rigorous evaluation, architecture trade-offs
10	hierarchical	Tree (multi-level)	Lead → coordinators → workers	Large teams, domain separation

Pattern Details

1. fan-out — Parallel Workers

fanOut([
  { task: "Review auth.ts", name: "AuthReviewer" },
  { task: "Review db.ts", name: "DbReviewer" },
], { cli: "claude" });

2. pipeline — Sequential Stages

pipeline([
  { task: "Design the API schema", name: "Designer" },
  { task: "Implement the endpoints", name: "Implementer" },
  { task: "Write integration tests", name: "Tester" },
]);

3. hub-spoke — Persistent Coordinator

hubAndSpoke({
  hub: { task: "Coordinate building a REST API", name: "Lead" },
  workers: [
    { task: "Build database models", name: "DbWorker" },
    { task: "Build route handlers", name: "ApiWorker" },
  ],
});

4. consensus — Cooperative Voting

consensus({
  proposal: "Should we migrate to Fastify?",
  voters: [
    { task: "Evaluate performance", name: "PerfExpert" },
    { task: "Evaluate DX", name: "DxExpert" },
  ],
  consensusType: "majority",
});

5. mesh — Peer Collaboration

mesh({
  goal: "Debug the auth flow returning 500",
  agents: [
    { task: "Check server logs", name: "LogAnalyst" },
    { task: "Review auth code", name: "CodeReviewer" },
    { task: "Write repro test", name: "Tester" },
  ],
});

6. handoff — Dynamic Routing

handoff({
  entryPoint: { task: "Triage the request", name: "Triage" },
  routes: [
    { agent: { task: "Handle billing", name: "Billing" }, condition: "billing, payment" },
    { agent: { task: "Handle tech issues", name: "TechSupport" }, condition: "error, bug" },
  ],
  maxHandoffs: 3,
});

7. cascade — Cost-Aware Escalation

cascade({
  tiers: [
    { agent: { task: "Answer this", cli: "claude" }, confidenceThreshold: 0.7, costWeight: 1 },
    { agent: { task: "Answer this", cli: "claude" }, confidenceThreshold: 0.85, costWeight: 5 },
    { agent: { task: "Answer this", cli: "claude" }, costWeight: 20 },
  ],
});

8. dag — Directed Acyclic Graph

dag({
  nodes: [
    { id: "scaffold", task: "Create project scaffold" },
    { id: "frontend", task: "Build React UI", dependsOn: ["scaffold"] },
    { id: "backend", task: "Build API", dependsOn: ["scaffold"] },
    { id: "integrate", task: "Wire together", dependsOn: ["frontend", "backend"] },
  ],
  maxConcurrency: 3,
});

9. debate — Adversarial Refinement

debate({
  topic: "Monorepo vs polyrepo for the new platform?",
  debaters: [
    { task: "Argue for monorepo", position: "monorepo" },
    { task: "Argue for polyrepo", position: "polyrepo" },
  ],
  judge: { task: "Judge and decide", name: "ArchJudge" },
  maxRounds: 3,
});

10. hierarchical — Multi-Level Delegation

hierarchical({
  agents: [
    { id: "lead", task: "Coordinate full-stack app", role: "lead" },
    { id: "fe-coord", task: "Manage frontend", role: "coordinator", reportsTo: "lead" },
    { id: "be-coord", task: "Manage backend", role: "coordinator", reportsTo: "lead" },
    { id: "fe-dev", task: "Build components", role: "worker", reportsTo: "fe-coord" },
    { id: "be-dev", task: "Build API", role: "worker", reportsTo: "be-coord" },
  ],
});

Reflection Protocol

All patterns support reflection — periodic synthesis that enables course correction. Enabled via reflectionThreshold on WorkflowOptions.

{
  reflectionThreshold: 10, // trigger after 10 agent messages
  onReflect: async (ctx) => {
    // Examine ctx.recentMessages, ctx.agentStatuses
    // Return adjustments or null
  },
}

Common Mistakes

Mistake	Why It Fails	Fix
Using mesh for everything	O(n^2) communication, debugging nightmare	Use hub-spoke for most tasks
Pipeline for independent work	Sequential bottleneck	Use fan-out or dag
Hub-spoke for simple parallel tasks	Hub is unnecessary overhead	Use fan-out
Consensus for non-decisions	Voting on implementation tasks wastes time	Use hub-spoke, let lead decide
No circuit breaker on handoff	Infinite routing loops	Always set maxHandoffs
Cascade without confidence parsing	Agents don't report confidence	Convention injection handles this
Hierarchical for 3 agents	Management overhead exceeds benefit	Use hub-spoke for small teams

DAG Executor — Proven Pattern

Agent Completion: Detect → Release → Collect

Agent writes summary file → Orchestrator polls (5s) → Detects new mtime →
  Reads summary → Calls client.release(agent) → agent_exited fires → Node marked complete

State & Resume

saveState(completed, depsOutput, results, startTime);
// Restart with --resume to skip completed nodes

YAML Workflow Definition

Any pattern can be defined in YAML for portability:

version: "1.0"
name: feature-dev
pattern: hub-spoke
agents:
  - id: lead
    role: lead
    cli: claude
  - id: developer
    role: worker
    cli: codex
    reportsTo: lead
steps:
  - id: plan
    agent: lead
    prompt: "Create a development plan for: {{task}}"
    expects: "PLAN_COMPLETE"
  - id: implement
    agent: developer
    dependsOn: [plan]
    prompt: "Implement: {{steps.plan.output}}"
    expects: "DONE"
reflection:
  enabled: true
  threshold: 10
trajectory:
  enabled: true