Why role design matters more than agent count

Most multi-agent failures are job-description failures rather than intelligence failures.

Two agents with crisp roles outperform six with overlapping ones, reliably. System performance tracks the quality of your role boundaries far more closely than it tracks headcount.

Fuzzy boundaries bill you twice

Overlap. Two agents both handle the same responsibility. You pay duplicate tokens and then pay again to reconcile conflicting outputs, and reconciliation is the expensive part, because someone has to decide which version is right.

Gaps. Each agent assumed the other covered it. Nobody did. The omission ships silently, and unlike overlap it produces no conflicting artifact to notice.

Overlap costs money. Gaps cost trust. Both come from the same defect: nobody wrote the boundary down.

The role charter

One page per agent, four fields:

• Owns: the outcomes this agent is accountable for, plus the explicit not-list. The not-list is the half that gets skipped and the half that prevents overlap.
• Tools: only what the role requires. Permission scope is role scope; if the researcher has deploy credentials, its role is larger than its description.
• Interface: exactly what it receives, exactly what it produces, in what format.
• Done: the criteria its output is judged against, checkable by whoever consumes it.

Write these before the prompts. You will find the charter largely is the prompt, which is the point: a system prompt is a job description with worse formatting.

The audit that catches drift

Print every charter side by side. Look for two things:

Responsibilities claimed by two agents. Responsibilities claimed by none.

Ten minutes, once a quarter, and it is cheaper than any incident it prevents. Roles drift as features get added under deadline, and nobody notices until two agents are quietly disagreeing about who handles refunds.

A useful deletion test

For each agent, ask: if this were removed, what specifically would get worse?

If the answer is hard to articulate, the role is not pulling its weight, and its responsibilities probably belong to a neighbour. Removing an agent is a legitimate architectural improvement and it happens far less often than adding one.

Clear roles prevent expensive confusion. Watch a film crew: the gaffer does not grade the footage, the editor does not light the scene, and everyone knows whose call is whose. That precision is how two hundred people make one coherent film.

If you printed your agents' role descriptions today, would any two of them overlap?