Agent Architecture Patterns

Agent Architecture Patterns

Most agent failures are architectural, not prompt-level.

Pick the pattern that matches the task's decision shape, not the framework that's trending. The wrong pattern multiplies cost, latency, and failure modes.

When to use this skill

• The user is sketching a new agent or rewriting an existing one.
• The user describes symptoms — looping, drifting, exceeding budget, losing context — that point at the architecture, not the prompt.
• The user names a framework (LangGraph, AutoGen, CrewAI, Swarm) and wants to know which pattern to instantiate.
• The user is comparing single-agent vs. multi-agent for a given workload.

Decision flow

Walk this top-down before recommending anything.

1. Is the task a single turn with deterministic tools? → no agent. Use a typed tool call.
2. Is the path knowable up front? → Plan-and-Execute. Plan once, execute steps, no re-planning unless a step fails.
3. Is the path discoverable only by trying? → ReAct. Tight think→act→observe loop, one step at a time.
4. Does the task need self-correction on quality (not just errors)? → wrap the executor in Reflexion / critic-actor.
5. Are there ≥3 disjoint skills (e.g. SQL, code, search) with no shared state? → Router dispatches a single sub-agent per turn.
6. Do sub-agents need to collaborate, hand off, or argue? → Supervisor owns the conversation and delegates; sub-agents do not talk to each other directly.
7. Are there ≥2 tiers of decomposition (team-of-teams)? → Hierarchical. Use sparingly — debuggability collapses fast.

Default to the simplest pattern that fits. Escalate only on evidence.

The patterns in one line each

• ReAct — interleaved reasoning + action in a single loop. Cheap, observable, brittle on long tasks.
• Plan-and-Execute — produce a plan, then execute it. Cuts token cost vs. ReAct on long tasks; brittle if the world changes mid-plan.
• Reflexion — actor proposes, critic scores, actor revises. Buys quality at 2–4× cost. Cap iterations hard.
• Router — one classifier picks one downstream skill per turn. Not multi-agent — it's switch with an LLM.
• Supervisor — a coordinator agent owns state and dispatches workers. Workers are stateless from each other's POV.
• Hierarchical — supervisors of supervisors. Last resort.
• Swarm / handoff — peer agents pass control via explicit handoff tools. Useful for role-shaped tasks (triage → specialist), dangerous for open-ended ones.

See references/patterns.md for the full per-pattern brief — when each works, when each fails, and the minimal control-flow sketch.

Anti-patterns to flag immediately

• Multi-agent for parallelism alone. If sub-agents don't need different tools, prompts, or memories, you want concurrent tool calls, not agents.
• Free-form agent-to-agent chat. Round-robin debates blow tokens and rarely converge. Force structured handoffs with explicit termination.
• Unbounded ReAct loops. Every ReAct agent needs a max-step cap and a budget check inside the loop, not only at the edge.
• Shared mutable memory across agents. Causes context poisoning. Pass explicit messages instead.
• One mega-prompt doing routing + execution + reflection. Separate the roles into separate calls; you can't debug what you can't isolate.

Picking the pattern: questions to ask the user

Before recommending anything, get answers to:

1. What's the input shape (single message, document, stream, ticket)?
2. What's the output contract (free text, JSON, side-effect on a system)?
3. What tools exist and how reliable are they?
4. What's the budget per task — latency and cost ceiling?
5. Is there a human in the loop, and at which step?
6. What does failure look like, and who notices?

If you can't answer these, you're not ready to pick a pattern — say so.

Evaluation, not vibes

Whatever pattern is chosen, demand:

• A golden set of ≥20 representative inputs before the first commit.
• Trace logging of every step (input, tool call, output) — see references/observability.md.
• A regression check before any prompt or graph change ships.

No eval harness, no architecture decision. Block the conversation on it.

Why this exists

The framework debate (LangGraph vs. AutoGen vs. CrewAI vs. Swarm) dominates the conversation; the pattern debate, which actually predicts success, barely happens. Naming the decision shape first — and only then picking the framework that implements it — flips the order. See [link to article on agent architecture patterns].

References

• references/patterns.md — full per-pattern brief (when to use, failure modes, control-flow sketch).
• references/frameworks.md — mapping patterns to LangGraph, AutoGen, CrewAI, OpenAI Swarm.
• references/observability.md — what to log, span shape, eval scaffolding.

Related skills

• Once a pattern is chosen, model its unit economics — [[agent-cost-modeling]].
• Budget per-stage latency before wiring it up — [[latency-budgeting]].
• Tools are part of the architecture — [[tool-use-schema-design]].
• Stand up the eval before shipping — [[agent-evaluation-harness]].
• Instrument the loop from day one — [[agent-observability]].