When to Choose ReAct vs Plan-and-Execute vs Multi-Agent
Use this page when you must pick a control pattern before writing orchestration code. It maps task shape to ReAct, Plan-and-Execute, multi-agent handoff, or a simple hybrid.
How to Use This List
- Start with the quick pick table, then confirm with the signal checklists.
- Prefer the simplest pattern that meets reliability, cost, and security needs.
- Revisit the choice when tool count, risk, or average turn count jumps in production metrics.
- Hybrids are allowed; document which pattern owns the top level.
Quick Pick Matrix
| If your task is mostly… | Prefer | Why |
|---|---|---|
| Unknown path, needs tools mid-flight | ReAct | Next step depends on each observation |
| Known multi-step structure, costly tools | Plan-and-Execute | Plan reduces redundant exploration |
| Multiple skills, models, or privilege tiers | Multi-agent | Real role boundaries pay off |
| Structured outer goal + messy inner tools | Hybrid: plan outer, ReAct inner | Auditability without rigidity |
| Repeatable product workflow | Template plan (± light ReAct) | Deterministic stages beat free agents |
| One tool, one turn | Not an agent loop | Script or single tool call is enough |
Task Shape Signals
| Signal | ReAct | Plan-and-Execute | Multi-agent |
|---|---|---|---|
| Next action depends on last tool result | Strong fit | Weak alone | Optional inside specialists |
| Clear ordered milestones | Optional | Strong fit | Plan can assign owners |
| >1 trust level or tool belt | Poor (too wide) | Medium | Strong fit |
| Human approval of the approach | Hard (no artifact) | Strong (review plan) | Strong (stage gates) |
| Latency sensitivity (few turns) | Medium | Medium | Often worse (coordination) |
| Cost sensitivity (token/tool $) | Can thrash | Often better | Can multiply cost |
| Need audit of "why step N" | Trajectory logs | Plan + step logs | Handoff + role logs |
| Open-ended exploration | Strong fit | Risk of bad plans | Only if roles help search |
Complexity vs Predictability
| Low predictability (path unknown) | High predictability (path known) | |
|---|---|---|
| Low complexity | Bounded ReAct or single tool call | Script / fixed workflow (skip agent) |
| Medium complexity | ReAct with tight tools + max turns | Plan-and-Execute with light replan |
| High complexity | Hybrid: coarse plan + ReAct steps | Multi-step plan; multi-agent if roles differ |
Security and Privilege Cheatsheet
| Requirement | Pattern guidance |
|---|---|
| One low-risk tool belt | Single ReAct or plan/execute agent |
| Read-only vs write tools must not mix freely | Multi-agent or staged plan with gates |
| Irreversible actions need approval | Plan gate or human node before execute |
| Untrusted web/email content in tools | Narrow specialist; never shared superuser tools |
| Compliance boundary between departments | Multi-agent with separate credentials |
Cost and Ops Cheatsheet
| Metric rising in prod | Architectural move |
|---|---|
| Avg turns per success climbing | Add plan structure or cut tools |
| Repeated identical tool calls | Dedupe + stop policy; consider plan slots |
| Context tokens dominated by tool JSON | Summarize observations; artifact store |
| Many roles but one prompt | Split specialists with real allowlists |
| Orchestrator doing all work | Fix routing; specialists must own subgoals |
| Replan storms | Cap replans; fix verification flakiness |
Default Decision Order
- Can a script or single tool call finish it? If yes, do not start an agent loop.
- Is the path mostly known? If yes, start Plan-and-Execute (or a template plan).
- Is the path discovery-heavy? If yes, start bounded ReAct.
- Do roles, models, or privileges actually differ? If yes, add multi-agent handoff.
- Do you need both structure and messy tools? If yes, hybrid: plan outside, ReAct inside.
- Write stop conditions and budgets before tools. Pattern choice does not replace bounds.
Anti-Defaults (Avoid These Defaults)
| Tempting default | Why it fails | Better default |
|---|---|---|
| Multi-agent from day one | Coordination without need | Single bounded ReAct |
| Infinite ReAct "until done" | Cost and thrash | Max turns + goal check |
| 30-step plans for simple asks | Overhead and brittleness | 3-7 milestones or pure ReAct |
| One agent, all production tools | Security and prompt overload | Least privilege / specialists |
| Hybrid soup with no top owner | Unclear control flow | Name the top-level pattern |
FAQs
What is the safest first architecture for a new agent?
A single ReAct agent with a small tool allowlist, max turns, timeout, and a clear done condition - unless the workflow is already a fixed checklist, in which case use a template plan.
When is multi-agent worth the complexity?
When specialists need different tools, prompts, models, or trust levels, or when human gates must sit between stages. Same tools with different names is not enough.
Can I switch patterns later without a rewrite?
Yes if you kept tools, state, and stop policies modular. Many teams start ReAct, then wrap a planner or router around the same tools.
Does a stronger model change the recommendation?
It can reduce reasoning errors inside a pattern, but it does not remove the need for bounds, privilege separation, or plans on long structured jobs.
How do I choose between plan-and-execute and a hybrid?
If steps are clean and tools are reliable, pure plan/execute is enough. If each step needs exploratory tool use, budget a small ReAct loop per step.
What metrics should drive a pattern change?
Turn count, tool repeat rate, cost per successful task, handoff failure rate, and % stops that are max-turns versus goal-complete.
Is "agent team" marketing the same as multi-agent handoff?
Not always. Look for real role prompts, tool allowlists, and handoff contracts - not only multiple character names in one prompt.
When should I refuse to use an agent architecture at all?
When inputs and outputs are deterministic, tools are fixed, and branching fits ordinary code. Agents earn their keep under ambiguity or multi-step tool choice.
How many specialists is too many?
If the orchestrator cannot explain each role's unique tools and success contract in one sentence, you have too many. Start with two and split only on pain.
Where do stopping conditions show up in this choice?
Everywhere. Every pattern needs global budgets; multi-agent also needs per-specialist budgets and handoff depth caps.
What is a good architecture one-pager for a design review?
Name the top-level pattern, draw the loop or graph, list tools per node, list stop conditions, and state why simpler patterns were rejected.
Should product and research agents use the same default?
Often no. Research leans ReAct or hybrid; productized business flows lean template plans with narrow tools and stage gates.
Related
- The Three Core Agent Architecture Patterns, Compared - pattern definitions
- ReAct: Reasoning and Acting in an Interleaved Loop - ReAct deep dive
- Plan-and-Execute: Separating Planning from Execution - planning deep dive
- Multi-Agent Handoff: Specialist Agents Passing Work to Each Other - handoff deep dive
- Hybrid Architectures: Combining Planning, Reaction, and Delegation - blending patterns
- Agent Architectures Best Practices - ten guidelines
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