Multi-agent systems: when you actually need them (usually you don't)
Supervisor patterns and planner-retriever-synthesizer architectures are elegant on a slide. Here's an honest look at when multiple coordinating agents beat one well-tooled agent — and when they just add failure modes.
Multi-agent systems are having a moment — a supervisor delegating to specialists, a crew dividing the work. They make for a great architecture diagram. They also, most of the time, solve a problem you don't have while adding several you now do. Here's an honest take on when they earn their complexity.
The patterns
- Supervisor — a manager agent routes each subtask to a specialist agent and combines the results.
- Planner-retriever-synthesizer — one agent plans, another gathers information, a third writes the answer.
- Debate / critique — agents check or argue with each other to improve quality.
The cost nobody puts on the slide
- More calls, more cost, more latency — every agent is another chain of LLM calls.
- More non-determinism — several stochastic components compound into a less predictable whole.
- Coordination failures — handoffs drop context, agents disagree, and errors cascade across the boundary.
- Harder to debug and eval — you now have to trace and evaluate a small society, not one component.
When one agent wins
A single agent with a good set of tools and a clear prompt handles the large majority of tasks a 'crew' is pitched for — and it's far easier to debug, eval, and trust. Before you build three agents, try making one really good one. Usually that's the answer.
When multi-agent genuinely earns its keep
- Separable expertise — genuinely distinct skills or toolsets that don't belong in one prompt.
- Parallelism that cuts latency — independent subtasks that can truly run at once.
- Context isolation — each agent keeps a focused window instead of one bloated shared context.
- Independent scaling — parts of the system that need to scale or fail independently.
Most multi-agent systems are a single well-tooled agent wearing a costume. Add agents when the problem is genuinely plural — not because three boxes look more impressive than one.