# Why and When to Use Multiple Agents — LangGraph Agents & Multi-Agent Systems

Source: https://www.geekswithgeeks.com/en/langgraph-agents/x-why

> Weigh the benefits against the added cost and complexity.

## Specialisation has a price

A single agent with too many tools and a long prompt gets confused: it picks the wrong tool, forgets rules and becomes hard to test. Splitting the work into **specialised agents** (a researcher, a coder, a reviewer, a billing expert), each with a short prompt and a small tool set, can improve reliability, let you use **different models** per role and allow independent testing and ownership. The costs are real: more model calls, more latency and tokens, **coordination bugs** (agents repeating work or contradicting each other), harder debugging and a larger attack surface. Start with one agent or a workflow graph; split only when a single agent measurably fails.

## Specialists and a coordinator

Split a big job among focused agents, then coordinate them with a supervisor or hand-offs.

![Four patterns: supervisor, hand-off, sub-graph, hierarchy.](assets/figures/langgraph-agents/section-6-map.svg) — Figure 6.1 — Supervisor, hand-off, sub-graph and hierarchy.

## One agent versus many

A rough comparison to guide the decision.

```text
                      single agent / workflow         multiple agents
prompt + tools        one big set (can confuse)       small, focused per role
model choice          one model                       cheaper/stronger per role
cost, latency         lowest                          higher (more calls, more tokens)
debugging             one trace                       many traces + hand-offs
failure modes         wrong tool, forgotten rules     loops between agents, duplicated work
start here?           YES                             only after measuring a single-agent failure
```

**Quiz:** What is a real cost of multi-agent systems?

- [ ] They are always cheaper
- [x] More calls, latency and coordination bugs
- [ ] They remove the need for testing
- [ ] They need no prompts

*Answer:* More calls, latency and coordination bugs. More moving parts mean more cost and more ways to fail.